2023/04/03 更新

写真a

ヨコヤマ シュウイチロウ
横山 修一郎
YOKOYAMA Shuichiro
所属
素粒子宇宙起源研究所 基礎理論研究部門 助教
大学院担当
大学院理学研究科
職名
助教

学位 1

  1. 理学(博士) ( 2008年3月   京都大学 ) 

研究キーワード 2

  1. 宇宙論、インフレーション

  2. 宇宙大規模構造形成

研究分野 1

  1. 自然科学一般 / 素粒子、原子核、宇宙線、宇宙物理にする理論

経歴 4

  1. 名古屋大学   助教

    2018年8月 - 現在

  2. 立教大学   助教

    2014年9月 - 2018年7月

  3. 東京大学   研究員

    2012年4月 - 2014年8月

  4. 名古屋大学   研究員

    2008年4月 - 2012年3月

 

論文 121

  1. Can primordial parity violation explain the observed cosmic birefringence? 査読有り

    Fujita Tomohiro, Minami Yuto, Shiraishi Maresuke, Yokoyama Shuichiro

    PHYSICAL REVIEW D   106 巻 ( 103529 )   2022年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.106.103529

  2. Effective Inspiral Spin Distribution of Primordial Black Hole Binaries 査読有り

    Koga Yasutaka, Harada Tomohiro, Tada Yuichiro, Yokoyama Shuichiro, Yoo Chul-Moon

    Astrophysical Journal   939 巻 ( 2 ) 頁: 65   2022年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.3847/1538-4357/ac93f1

  3. Sneutrinos as two inflatons and curvaton and leptogenesis 査読有り

    Takahashi Tomo, Yamada Toshifumi, Yokoyama Shuichiro

    Journal of Cosmology and Astroparticle Physics   11 巻 ( 021 )   2022年11月

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    担当区分:筆頭著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1088/1475-7516/2022/11/021

  4. Conceptual design and science cases of a juggled interferometer for gravitational wave detection 査読有り

    Wu Bin, Ishikawa Tomohiro, Iwaguchi Shoki, Shimizu Ryuma, Watanabe Izumi, Kawasaki Yuki, Michimura Yuta, Yokoyama Shuichiro, Kawamura Seiji

    PHYSICAL REVIEW D   106 巻 ( 042007 )   2022年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PhysRevD.106.042007

  5. Multi-chaotic inflation with and without spectator field 査読有り

    Morishita Yukiyoshi, Takahashi Tomo, Yokoyama Shuichiro

    Journal of Cosmology and Astroparticle Physics   07 巻 ( 042 )   2022年7月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1088/1475-7516/2022/07/042

  6. Simulation of primordial black holes with large negative non-Gaussianity 査読有り 国際共著

    Escriva Albert, Tada Yuichiro, Yokoyama Shuichiro, Yoo Chul-Moon

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2022 巻 ( 5 )   2022年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    In this work, we have performed numerical simulations of primordial black hole (PBH) formation in the Friedman-Lemaître-Robertson-Walker universe filled by radiation fluid, introducing the local-type non-Gaussianity to the primordial curvature fluctuation. We have compared the numerical results from simulations with previous analytical estimations on the threshold value for PBH formation done in the previous paper [1], particularly for negative values of the non-linearity parameter f NL. Our numerical results show the existence of PBH formation of (the so-called) type I also in the case f NL ≤2-0.336, which was not found in the previous analytical expectations using the critical averaged compaction function. In particular, although the universal value for the averaged critical compaction function ō o = 2/5 found previously in the literature is not satisfied for all the profiles considered in this work, an alternative direct analytical estimate has been found to be roughly accurate to estimate the thresholds, which gives the value of the critical averaged density with a few % deviation from the numerical one for f NL ≤3-1.

    DOI: 10.1088/1475-7516/2022/05/012

    Web of Science

    Scopus

  7. Primordial black holes in peak theory with a non-Gaussian tail 査読有り

    Kitajima Naoya, Tada Yuichiro, Yokoyama Shuichiro, Yoo Chul-Moon

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2021 巻 ( 10 ) 頁: 053 - 053   2021年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    In this paper, we update the peak theory for the estimation of the primordial black hole (PBH) abundance, particularly by implementing the critical behavior in the estimation of the PBH mass and employing the averaged compaction function for the PBH formation criterion to relax the profile dependence. We apply our peak theory to a specific non-Gaussian feature called the exponential tail, which is characteristic in ultra slow-roll models of inflation. With this type of non-Gaussianity, the probability of a large perturbation is not suppressed by the Gaussian factor but decays only exponentially, so the PBH abundance is expected to be much enhanced. Not only do we confirm this enhancement even compared to the case of the corresponding nonlinearity parameter f NL = 5/2, but also we find that the resultant PBH mass spectrum has a characteristic maximal mass which is not seen in the simple Press-Schechter approach.

    DOI: 10.1088/1475-7516/2021/10/053

    Web of Science

    Scopus

    その他リンク: https://iopscience.iop.org/article/10.1088/1475-7516/2021/10/053/pdf

  8. Statistically-anisotropic tensor bispectrum from inflation 査読有り

    Hiramatsu Takashi, Murai Kai, Obata Ippei, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2021 巻 ( 3 ) 頁: 047 - 047   2021年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    We develop a possibility of generating tensor non-Gaussianity in a kind of anisotropic inflation, where a U(1) gauge field is kinetically coupled to a spectator scalar field. Owing to this coupling, the coherent mode of the electric field appears and softly breaks the isotropy of the Universe. We compute the bispectrum of linearly-polarized tensor perturbations sourced by the gauge field and find that it is strongly red-tilted and has distinctive statistical anisotropies including higher-order multipole moments. Interestingly, the tensor bispectra with the specific combinations of linear polarization modes are dominant, and their amplitudes depend on the different sets of multipole moments. This new type of statistically-anisotropic tensor non-Gaussianity can be potentially testable with the upcoming cosmic microwave background B-mode polarization experiments.

    DOI: 10.1088/1475-7516/2021/03/047

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    Scopus

    その他リンク: https://iopscience.iop.org/article/10.1088/1475-7516/2021/03/047/pdf

  9. Blue-tilted inflationary tensor spectrum and reheating in the light of NANOGrav results 査読有り

    Kuroyanagi Sachiko, Takahashi Tomo, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2021 巻 ( 1 ) 頁: 071 - 071   2021年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2021/01/071

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    Scopus

    その他リンク: https://iopscience.iop.org/article/10.1088/1475-7516/2021/01/071

  10. UV sensitive one-loop matter power spectrum in degenerate higher-order scalar-tensor theories 査読有り

    Hirano Shin'ichi, Kobayashi Tsutomu, Yamauchi Daisuke, Yokoyama Shuichiro

    PHYSICAL REVIEW D   102 巻 ( 10 )   2020年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Review D  

    We study matter density perturbations up to third order and the one-loop matter power spectrum in degenerate higher-order scalar-tensor (DHOST) theories beyond Horndeski. We systematically solve gravitational field equations and fluid equations order by order and find three novel shape functions characterizing the third-order solution in DHOST theories. A complete form of the one-loop matter power spectrum is then obtained using the resultant second- and third-order solutions. We confirm the previous result that the convergence condition of the loop integrals in the infrared limit becomes more stringent than that of the standard one in general relativity. We show that also in the ultraviolet limit the convergence condition becomes more stringent and the one-loop matter power spectrum is thus sensitive to the short-wavelength behavior of the linear power spectrum.

    DOI: 10.1103/PhysRevD.102.103505

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    Scopus

    その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.102.103505/fulltext

  11. Conformal inflation in the metric-affine geometry 査読有り

    Mikura Y., Tada Y., Yokoyama S.

    EPL   132 巻 ( 3 ) 頁: 39001 - 39001   2020年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:EPL  

    DOI: 10.1209/0295-5075/132/39001

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    Scopus

    その他リンク: https://iopscience.iop.org/article/10.1209/0295-5075/132/39001/pdf

  12. Violation of slow-roll in nonminimal inflation 査読有り 国際共著

    Takahashi Tomo, Tenkanen Tommi, Yokoyama Shuichiro

    PHYSICAL REVIEW D   102 巻 ( 4 )   2020年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Review D  

    We show that a nonminimal coupling to gravity can not only make some inflationary models consistent with cosmological data, similar to the case of Higgs inflation, but can also invoke slow-roll violation to realize a graceful exit from inflation. In particular, this is the case in models where a destabilizing mechanism that ends inflation should be assumed when the model is minimally coupled to gravity. As explicit examples, we consider the power-law and inverse monomial inflation models with a nonminimal coupling to gravity. While these models are excluded in the minimally coupled case, we show that they can become viable again in nonminimally coupled scenarios. In most scenario we considered, reheating can be naturally realized via gravitational particle production but this depends on the underlying theory of gravity in a nontrivial way reheating can be naturally realized via gravitational particle production but that this depends on the underlying theory of gravity in a nontrivial way.

    DOI: 10.1103/PhysRevD.102.043524

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    Scopus

    その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.102.043524/fulltext

  13. Limits on primordial magnetic fields from primordial black hole abundance 査読有り

    Saga Shohei, Tashiro Hiroyuki, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2020 巻 ( 5 ) 頁: 039 - 039   2020年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2020/05/039

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    Scopus

    arXiv

    その他リンク: https://iopscience.iop.org/article/10.1088/1475-7516/2020/05/039

  14. A novel formulation of the primordial black hole mass function 査読有り

    Suyama Teruaki, Yokoyama Shuichiro

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   2020 巻 ( 2 )   2020年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Progress of Theoretical and Experimental Physics  

    DOI: 10.1093/ptep/ptaa011

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    Scopus

  15. Clustering of primordial black holes formed in a matter-dominated epoch 査読有り

    Matsubara Takahiko, Terada Takahiro, Kohri Kazunori, Yokoyama Shuichiro

    PHYSICAL REVIEW D   100 巻 ( 12 )   2019年12月

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    出版者・発行元:Physical Review D  

    DOI: 10.1103/PhysRevD.100.123544

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    arXiv

  16. A novel formulation of the PBH mass function 査読有り

    Teruaki Suyama, Shuichiro Yokoyama

        2019年12月

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    Computations of the primordial black hole (PBH) mass function discussed in
    the literature have conceptual issues. They stem from that the mass function is
    a differential quantity and the standard criterion of the PBH formation from
    the seed primordial fluctuations cannot be directly applied to the computation
    of the differential quantities. We propose a new criterion of the PBH formation
    which is an addition of one extra condition to the existing one. By doing this,
    we derive a formal expression of the PBH mass function without introducing any
    ambiguous interpretations which exist in the previous studies. Once the
    underlying primordial fluctuations are specified, the PBH mass function can be
    in principle determined by the new formula. As a demonstration of our
    formulation, we compute the PBH mass function analytically for the case where
    the perturbations are Gaussian and the space is one dimension.

    arXiv

  17. Secondary CMB temperature anisotropies from magnetic reheating 査読有り

    Saga Shohei, Ota Atsuhisa, Tashiro Hiroyuki, Yokoyama Shuichiro

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   490 巻 ( 3 ) 頁: 4419 - 4427   2019年12月

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    出版者・発行元:Monthly Notices of the Royal Astronomical Society  

    Spatially fluctuating primordial magnetic fields (PMFs) inhomogeneously reheat the Universe when they dissipate deep inside the horizon before recombination. Such an energy injection turns into an additional photon temperature perturbation. We investigate secondary cosmic microwave background (CMB) temperature anisotropies originated from this mechanism, which we call inhomogeneous magnetic reheating. We find that it can bring us information about non-linear coupling between PMFs and primordial curvature perturbations parametrized by bNL, which should be important for probing the generation mechanism of PMFs. In fact, by using current CMB observations, we obtain an upper bound on the non-linear parameter as log (bNL(Bλ/nG)2) ≲− 36.5nB − 94.0 with Bλ and nB being a magnetic field amplitude smoothed over λ = 1 Mpc scale and a spectral index of the PMF power spectrum, respectively. Our constraints are far stronger than a previous forecast based on the future CMB spectral distortion anisotropy measurements because inhomogeneous magnetic reheating covers a much wider range of scales, i.e. 1 Mpc−1 ≲ k ≲ 1015 Mpc−1

    DOI: 10.1093/mnras/stz2882

    Web of Science

    Scopus

    arXiv

  18. Clustering of primordial black holes with non-Gaussian initial fluctuations 査読有り

    Suyama Teruaki, Yokoyama Shuichiro

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   2019 巻 ( 10 )   2019年10月

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    出版者・発行元:Progress of Theoretical and Experimental Physics  

    DOI: 10.1093/ptep/ptz105

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    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/1906.04958v2

  19. Redshift space distortions in the presence of non-minimally coupled dark matter 査読有り

    Chibana F., Kimura R., Yamaguchi M., Yamauchi D., Yokoyama S.

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2019 巻 ( 10 )   2019年10月

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    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    In this paper, we fully investigate cosmological scenarios in which dark matter is non-minimally coupled to an extra scalar degree of freedom. The interaction is realized by means of conformal and disformal terms in the transformed gravitational metric. Considering linear perturbation theory, we show that the growth rate of dark matter differs from the uncoupled case and that the well-known Kaiser formula undergoes modification. As a result, redshift space distortion measurements cease to be a direct probe of the linear growth rate of total matter, since the distortion factor has an extra, coupling-dependent term. We study the effect of the coupling in three cosmological models, two conformally and one disformally coupled, and forecast the constraints on the coupling, and other cosmological parameters, from future galaxy surveys.

    DOI: 10.1088/1475-7516/2019/10/049

    Web of Science

    Scopus

    arXiv

  20. Abundance of primordial black holes with local non-Gaussianity in peak theory 査読有り

    Yoo Chul-Moon, Gong Jinn-Ouk, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2019 巻 ( 9 )   2019年9月

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    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2019/09/033

    Web of Science

    Scopus

    arXiv

  21. Primordial black hole tower: Dark matter, earth-mass, and LIGO black holes 査読有り

    Tada Yuichiro, Yokoyama Shuichiro

    PHYSICAL REVIEW D   100 巻 ( 2 )   2019年7月

  22. Constraining degenerate higher-order scalar-tensor theories with linear growth of matter density fluctuations 査読有り

    Hirano Shin'ichi, Kobayashi Tsutomu, Yamauchi Daisuke, Yokoyama Shuichiro

    PHYSICAL REVIEW D   99 巻 ( 10 )   2019年5月

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    出版者・発行元:Physical Review D  

    DOI: 10.1103/PhysRevD.99.104051

    Web of Science

    Scopus

    arXiv

  23. Constraining degenerate higher-order scalar-tensor theories with density perturbations at linear order 査読有り

    Shin'ichiro Hirano, Tsutomu Kobayashi, Daisuke Yamauchi, Shuichiro Yokoyama

    Physical Review D   99 巻 ( 104051 )   2019年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

  24. Constraints on Earth-mass primordial black holes from OGLE 5-year microlensing events 査読有り

    Niikura Hiroko, Takada Masahiro, Yokoyama Shuichiro, Sumi Takahiro, Masaki Shogo

    PHYSICAL REVIEW D   99 巻 ( 8 )   2019年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Review D  

    DOI: 10.1103/PhysRevD.99.083503

    Web of Science

    Scopus

    arXiv

    その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.99.083503/fulltext

  25. Probing primordial non-Gaussianity with 21 cm fluctuations from minihalos 査読有り

    Sekiguchi Toyokazu, Takahashi Tomo, Tashiro Hiroyuki, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2019 巻 ( 2 ) 頁: 033 - 033   2019年2月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    We investigate future constraints on primordial local-type non-Gaussianity from 21 cm angular power spectrum from minihalos. We particularly focus on the trispectrum of primordial curvature perturbations which are characterized by the non-linearity parametersτ NL and g NL . We show that future measurements of minihalo 21 cm angular power spectrum can probe these non-linearity parameters with an unprecedented precision of τ NL ∼ 30 and g NL ∼ 2 × 10 3 for Square Kilometre Array (SKA) and τ NL ∼ 0.6 and g NL ∼ 8 × 10 2 for Fast Fourier Transform Telescope (FFTT). These levels of sensitivity would give significant implications for models of the inflationary Universe and the origin of cosmic density fluctuations.

    DOI: 10.1088/1475-7516/2019/02/033

    Web of Science

    Scopus

    arXiv

  26. Hunting for statistical anisotropy in tensor modes with B-mode observations 査読有り

    Hiramatsu Takashi, Yokoyama Shuichiro, Fujita Tomohiro, Obata Ippei

    PHYSICAL REVIEW D   98 巻 ( 8 )   2018年10月

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    出版者・発行元:Physical Review D  

    DOI: 10.1103/PhysRevD.98.083522

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/1808.08044v1

  27. Limits on primordial magnetic fields from direct detection experiments of gravitational wave background 査読有り

    Saga Shohei, Tashiro Hiroyuki, Yokoyama Shuichiro

    PHYSICAL REVIEW D   98 巻 ( 8 )   2018年10月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Review D  

    DOI: 10.1103/PhysRevD.98.083518

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    Scopus

    その他リンク: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.98.083518/fulltext

  28. Erratum: Primordial Black Hole Scenario for the Gravitational-Wave Event GW150914 [Phys. Rev. Lett. 117, 061101 (2016)].

    Sasaki M, Suyama T, Tanaka T, Yokoyama S

    Physical review letters   121 巻 ( 5 ) 頁: 059901   2018年8月

  29. Matter bispectrum beyond Horndeski theories 査読有り

    Hirano Shin'ichi, Kobayashi Tsutomu, Tashiro Hiroyuki, Yokoyama Shuichiro

    PHYSICAL REVIEW D   97 巻 ( 10 )   2018年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Review D  

    DOI: 10.1103/PhysRevD.97.103517

    Web of Science

    Scopus

    arXiv

  30. Hidden Universality in the Merger Rate Distribution in the Primordial Black Hole Scenario 査読有り

    Bence Kocsis, Teruaki Suyama, Takahiro Tanaka, Shuichiro Yokoyama

    Astrophysical Journal   854 巻 ( 1 )   2018年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Institute of Physics Publishing  

    It has been proposed that primordial black holes (PBHs) form binaries in the radiation dominated era. Once formed, some fraction of them may merge within the age of the universe by gravitational radiation reaction. We investigate the merger rate of the PBH binaries when the PBHs have a distribution of masses around O(10)M, which is a generalization of the previous studies where the PBHs are assumed to have the same mass. After deriving a formula for the merger time probability distribution in the PBH mass plane, we evaluate it under two different approximations. We identify a quantity constructed from the mass distribution of the merger rate density per unit cosmic time and comoving volume R(m1, m2), α = -(m1+ m2)2∂2 In R/∂m1∂m2, which universally satisfies 0.97≲α≲ 1.05 for all binary masses independently of the PBH mass function. This result suggests that the measurement of this quantity is useful for testing the PBH scenario.

    DOI: 10.3847/1538-4357/aaa7f4

    Scopus

    arXiv

  31. Primordial black holes - Perspectives in gravitational wave astronomy 査読有り

    Misao Sasaki, Teruaki Suyama, Takahiro Tanaka, Shuichiro Yokoyama

    Classical and Quantum Gravity   35 巻 ( 6 )   2018年2月

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    記述言語:英語   出版者・発行元:Institute of Physics Publishing  

    This article reviews current understanding of primordial black holes (PBHs), with particular focus on those massive examples (≳1015 g) which remain at the present epoch, not having evaporated through Hawking radiation. With the detection of gravitational waves by LIGO, we have gained a completely novel observational tool to search for PBHs, complementary to those using electromagnetic waves. Taking the perspective that gravitational-wave astronomy will make significant progress in the coming decades, the purpose of this article is to give a comprehensive review covering a wide range of topics on PBHs. After discussing PBH formation, as well as several inflation models leading to PBH production, we summarize various existing and future observational constraints. We then present topics on formation of PBH binaries, gravitational waves from PBH binaries, and various observational tests of PBHs using gravitational waves.

    DOI: 10.1088/1361-6382/aaa7b4

    Scopus

    arXiv

  32. 21 cm angular power spectrum from minihalos as a probe of primordial spectral runnings 査読有り

    Sekiguchi Toyokazu, Takahashi Tomo, Tashiro Hiroyuki, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2018 巻 ( 2 )   2018年2月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2018/02/053

    Web of Science

    Scopus

    arXiv

  33. Magnetic reheating 査読有り

    Saga Shohei, Tashiro Hiroyuki, Yokoyama Shuichiro

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   474 巻 ( 1 ) 頁: L52 - L55   2018年2月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Monthly Notices of the Royal Astronomical Society: Letters  

    DOI: 10.1093/mnrasl/slx195

    Web of Science

    Scopus

    arXiv

  34. Statistically Anisotropic Tensor Modes from Inflation 査読有り

    Tomohiro Fujita, Ippei Obata, Takahiro Tanaka, Shuichiro Yokoyama

        2018年1月

     詳細を見る

    We consider the inflationary universe with a spectator scalar field coupled
    to a $U(1)$ gauge field and calculate curvature perturbation and gravitational
    waves (GWs). We find that the sourced GWs can be larger than the one from
    vacuum fluctuation and they are statistically anisotropic as well as linearly
    polarized. The GW power spectrum acquires higher multipole moments as
    $\mathcal{P}_h \propto (1-\cos^2\theta+\cos^4\theta-\cos^6\theta)$ irrespective
    of the model parameters.

    DOI: 10.1088/1475-7516/2018/07/023

    arXiv

    その他リンク: http://arxiv.org/pdf/1801.02778v1

  35. Constraining modified theories of gravity with the galaxy bispectrum 査読有り

    Yamauchi Daisuke, Yokoyama Shuichiro, Tashiro Hiroyuki

    PHYSICAL REVIEW D   96 巻 ( 12 )   2017年12月

     詳細を見る

    出版者・発行元:Physical Review D  

    DOI: 10.1103/PhysRevD.96.123516

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/1709.03243v1

  36. Refined study of isocurvature fluctuations in the curvaton scenario 査読有り

    Kitajima Naoya, Langlois David, Takahashi Tomo, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2017 巻 ( 12 )   2017年12月

     詳細を見る

    記述言語:英語   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    We revisit the generation of dark matter isocurvature perturbations in the curvaton model in greater detail, both analytically and numerically. As concrete examples, we investigate the cases of thermally decoupled dark matter and axionic dark matter. We show that the radiation produced by the decay of the curvaton, which has not been taken into account in previous analytical studies, can significantly affect the amplitude of isocurvature perturbations. In particular, we find that they are drastically suppressed even when the dark matter freeze-out (or the onset of the axion oscillations for axionic dark matter) occurs before the curvaton decays, provided the freeze-out takes place deep in the curvaton-dominated Universe. As a consequence, we show that the current observational isocurvature constraints on the curvaton parameters are not as severe as usually thought.

    DOI: 10.1088/1475-7516/2017/12/042

    Web of Science

    Scopus

    arXiv

  37. Are redshift-space distortions actually a probe of growth of structure? 査読有り

    Rampei Kimura, Teruaki Suyama, Masahide Yamaguchi, Daisuke Yamauchi, Shuichiro Yokoyama

        2017年9月

     詳細を見る

    We present an impact of coupling between dark matter and a scalar field,
    which might be responsible for dark energy, on measurements of redshift-space
    distortions. We point out that, in the presence of conformal and/or disformal
    coupling, linearized continuity and Euler equations for total matter fluid
    significantly deviate from the standard ones even in the sub-horizon scales. In
    such a case, a peculiar velocity of total matter field is determined not only
    by a logarithmic time derivative of its density perturbation but also by
    density perturbations for both dark matter and baryon, leading to a large
    modification of the physical interpretation of observed data obtained by
    measurements of redshift-space distortions. We reformulate galaxy two-point
    correlation function in the redshift space based on the modified continuity and
    Euler equations. We conclude from the resultant formula that the true value of
    the linear growth rate of large-scale structure cannot be necessarily
    constrained by single-redshift measurements of the redshift-space distortions,
    unless one observes the actual time-evolution of structure.

    DOI: 10.1093/pasj/psy083

    arXiv

  38. Constraining the epoch-of-reionization model parameters with the 21-cm bispectrum 査読有り

    Shimabukuro Hayato, Yoshiura Shintaro, Takahashi Keitaro, Yokoyama Shuichiro, Ichiki Kiyotomo

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   468 巻 ( 2 ) 頁: 1542 - 1550   2017年6月

     詳細を見る

    出版者・発行元:Monthly Notices of the Royal Astronomical Society  

    DOI: 10.1093/mnras/stx530

    Web of Science

    Scopus

    arXiv

  39. Spin Distribution of Primordial Black Holes 査読有り

    Takeshi Chiba, Shuichiro Yokoyama

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   ( 8 )   2017年4月

     詳細を見る

    記述言語:英語   出版者・発行元:OXFORD UNIV PRESS INC  

    We estimate the spin distribution of primordial black holes based on the
    recent study of the critical phenomena in the gravitational collapse of a
    rotating radiation fluid. We find that primordial black holes are mostly slowly
    rotating.

    DOI: 10.1093/ptep/ptx087

    Web of Science

    arXiv

    その他リンク: http://arxiv.org/pdf/1704.06573v2

  40. Cosmology with the Square Kilometre Array by SKA-Japan 査読有り

    Yamauchi Daisuke, Ichiki Kiyotomo, Kohri Kazunori, Namikawa Toshiya, Oyama Yoshihiko, Sekiguchi Toyokazu, Shimabukuro Hayato, Takahashi Keitaro, Takahashi Tomo, Yokoyama Shuichiro, Yoshikawa Kohji

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   68 巻 ( 6 )   2016年12月

     詳細を見る

    出版者・発行元:Publications of the Astronomical Society of Japan  

    DOI: 10.1093/pasj/psw098

    Web of Science

    Scopus

    arXiv

  41. Multitracer technique for galaxy bispectrum - An application to constraints on non-local primordial non-Gaussianities - 査読有り

    Daisuke Yamauchi, Shuichiro Yokoyama, Keitaro Takahashi

    PHYSICAL REVIEW D   95 巻 ( 6 )   2016年11月

     詳細を見る

    記述言語:英語   出版者・発行元:AMER PHYSICAL SOC  

    We explore the use of galaxy bispectra with multitracer technique as a
    possible probe of primordial non-Gaussianities. We forecast future constraints
    on non-linearity parameters, $f_{\rm NL}^{\rm eq}$ and $f_{\rm NL}^{\rm orth}$,
    which respectively characterize the equilateral- and orthogonal-types
    primordial bispectra, and show that the multitracer analysis would be effective
    with reducing the cosmic-variance noise if the number density of galaxies is
    high enough. We find that the measurement of galaxy bispectrum by future galaxy
    surveys can reach the constraints on the non-local type primordial
    non-Gaussianities to the level severer than current one which has been obtained
    by cosmic microwave background observations.

    DOI: 10.1103/PhysRevD.95.063530

    Web of Science

    arXiv

  42. Constraining higher-order parameters for primordial non-Gaussianities from power spectra and bispectra of imaging surveys 査読有り

    Hashimoto Ichihiko, Taruya Atsushi, Matsubara Takahiko, Namikawa Toshiya, Yokoyama Shuichiro

    PHYSICAL REVIEW D   93 巻 ( 10 )   2016年5月

     詳細を見る

    出版者・発行元:Physical Review D  

    DOI: 10.1103/PhysRevD.93.103537

    Web of Science

    Scopus

    arXiv

  43. Constraining equilateral-type primordial non-Gaussianities from imaging surveys 査読有り

    Ichihiko Hashimoto, Shuntaro Mizuno, Shuichiro Yokoyama

    PHYSICAL REVIEW D   94 巻 ( 4 )   2016年5月

     詳細を見る

    記述言語:英語   出版者・発行元:AMER PHYSICAL SOC  

    We investigate expected constraints on equilateral-type primordial
    non-Gaussianities from future/ongoing imaging surveys, making use of the fact
    that they enhance the halo/galaxy bispectrum on large scales. As model
    parameters to be constrained, in addition to $f_{\rm NL}^{\rm equil}$, which is
    related to the primordial bispectrum, we consider $g_{\rm NL}^{(\partial
    \sigma)^4}$, which is related to the primordial trispectrum that appeared in
    the effective field theory of inflation. After calculating the angular
    bispectra of the halo/galaxy clustering and weak gravitational lensing based on
    the integrated perturbation theory, we perform Fisher matrix analysis for three
    representative surveys. We find that among the three surveys, the tightest
    constraints come from Large Synoptic Survey Telescope ; its expected $1\sigma$
    errors on $f_{\rm NL}^{\rm equil}$ and $g_{\rm NL}^{(\partial \sigma)^4}$ are
    respectively given by $7.0 \times 10^2$ and $4.9 \times 10^7$. Although this
    constraint is somewhat looser than the one from the current cosmic microwave
    background observation, since we obtain it independently, we can use this
    constraint as a cross check. We also evaluate the uncertainty with our results
    caused by using several approximations and discuss the possibility to obtain
    tighter constraint on $f_{\rm NL}^{\rm equil}$ and $g_{\rm NL}^{(\partial
    \sigma)^4}$.

    DOI: 10.1103/PhysRevD.94.043532

    Web of Science

    arXiv

  44. 21 cm line bispectrum as a method to probe cosmic dawn and epoch of reionization 査読有り

    Shimabukuro Hayato, Yoshiura Shintaro, Takahashi Keitaro, Yokoyama Shuichiro, Ichiki Kiyotomo

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   458 巻 ( 3 ) 頁: 3003 - 3011   2016年5月

     詳細を見る

    出版者・発行元:Monthly Notices of the Royal Astronomical Society  

    DOI: 10.1093/mnras/stw482

    Web of Science

    Scopus

    arXiv

  45. Ultra slow-roll G-inflation 査読有り

    Shin'ichi Hirano, Tsutomu Kobayashi, Shuichiro Yokoyama

    PHYSICAL REVIEW D   94 巻 ( 10 )   2016年4月

     詳細を見る

    記述言語:英語   出版者・発行元:AMER PHYSICAL SOC  

    The conventional slow-roll approximation is broken in the so-called "ultra
    slow-roll" models of inflation, for which the inflaton potential is exactly (or
    extremely) flat. The interesting nature of (canonical) ultra slow-roll
    inflation is that the curvature perturbation grows on superhorizon scales, but
    has a scale-invariant power spectrum. We study the ultra slow-roll inflationary
    dynamics in the presence of non-canonical kinetic terms of the scalar field,
    namely ultra slow-roll G-inflation. We compute the evolution of the curvature
    perturbation and show that the primordial power spectrum follows a broken power
    law with an oscillation feature. It is demonstrated that this could explain the
    lack of large-scale power in the cosmic microwave background temperature
    anisotropies. We also point out that the violation of the null energy condition
    is prohibited in ultra slow-roll G-inflation and hence a blue tensor tilt is
    impossible as long as inflation is driven by the potential. This statement is,
    however, not true if the energy density is dominated by the kinetic energy of
    the scalar field.

    DOI: 10.1103/PhysRevD.94.103515

    Web of Science

    arXiv

  46. Primordial Black Hole Scenario for the Gravitational-Wave Event GW150914. 査読有り

    Sasaki M, Suyama T, Tanaka T, Yokoyama S

    Physical review letters   117 巻 ( 6 ) 頁: 061101   2016年3月

     詳細を見る

  47. Studying 21cm power spectrum with one-point statistics 査読有り

    Shimabukuro Hayato, Yoshiura Shintaro, Takahashi Keitaro, Yokoyama Shuichiro, Ichiki Kiyotomo

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   451 巻 ( 1 ) 頁: 467 - 474   2015年7月

     詳細を見る

    記述言語:英語   出版者・発行元:Monthly Notices of the Royal Astronomical Society  

    The redshifted 21cm line signal from neutral hydrogens is a promising tool to probe the cosmic dawn and the epoch of reionization. Ongoing and future low-frequency radio experiments are expected to detect its fluctuations, especially through the power spectrum. In this paper, we give a physical interpretation of the time evolution of the power spectrum of the 21cm brightness temperature fluctuations, which can be decomposed into dark matter density, spin temperature and neutral fraction of hydrogen fluctuations. From the one-point statistics of the fluctuations, such as variance and skewness, we find that the peaks and dips in the time evolution are deeply related to X-ray heating of the intergalactic gas, which controls the spin temperature. We suggest the skewness of the brightness temperature distribution is a key observable to identify the onset of X-ray heating.

    DOI: 10.1093/mnras/stv965

    Web of Science

    Scopus

    arXiv

  48. Primordial black holes as biased tracers 査読有り

    Yuichiro Tada, Shuichiro Yokoyama

    Physical Review D - Particles, Fields, Gravitation and Cosmology   91 巻 ( 12 )   2015年6月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society  

    Primordial black holes (PBHs) are theoretical black holes which can be formed during the radiation dominant era through the gravitational collapse of radiational overdensities. It has been well known that in the context of the structure formation in our Universe such collapsed objects, e.g., halos/galaxies, could be considered as bias tracers of underlying matter fluctuations and the halo/galaxy bias has been studied well. Applying such a biased tracer picture to PBHs, we investigate the large scale clustering of PBHs and obtain an almost mass-independent constraint to the scenario that the dark matter (DM) consists of PBHs. We focus on the case where the statistics of the primordial curvature perturbations is almost Gaussian, but with small local-type non-Gaussianity. If PBHs account for the DM abundance, such a large scale clustering of PBHs behaves as nothing but the matter isocurvature perturbation which is strictly constrained by the observations of cosmic microwave backgrounds (CMBs). From this constraint, we show that, in the case where a certain single field causes both CMB temperature perturbations and PBH formation, the PBH-DM scenario is excluded even with quite small local-type non-Gaussianity, |fNL|∼O(0.01).

    DOI: 10.1103/PhysRevD.91.123534

    Scopus

  49. Halo/galaxy bispectrum with equilateral-type primordial trispectrum 査読有り

    Shuntaro Mizuno, Shuichiro Yokoyama

    Physical Review D - Particles, Fields, Gravitation and Cosmology   91 巻 ( 12 )   2015年6月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society  

    We investigate the effect of equilateral-type primordial trispectrum on the halo/galaxy bispectrum. We consider three types of equilateral primordial trispectra which are generated by quartic operators naturally appearing in the effective field theory of inflation and can be characterized by three nonlinearity parameters, gNLσ4, gNLσ2(∂σ)2, and gNL(∂σ)4. Recently, constraints on these parameters have been investigated from Cosmic Microwave Background (CMB) observations by using WMAP9 data. In order to consider the halo/galaxy bispectrum with the equilateral-type primordial trispectra, we adopt the integrated perturbation theory in which the effects of primordial non-Gaussianity are wholly encapsulated in the linear primordial polyspectrum for the evaluation of the biased polyspectrum. We show the shapes of the halo/galaxy bispectrum with the equilateral-type primordial trispectra and find that the primordial trispectrum characterized by gNLσ4 provides the same scale dependence as the gravity-induced halo/galaxy bispectrum. Hence, it would be difficult to obtain the constraint on gNLσ4 from the observations of the halo/galaxy bispectrum. On the other hand, the primordial trispectra characterized by gNLσ2(∂σ)2 and gNL(∂σ)4 provide the common scale dependence which is different from that of the gravity-induced halo/galaxy bispectrum on large scales. Hence, future observations of the halo/galaxy bispectrum would give constraints on the nonlinearity parameters, gNLσ2(∂σ)2 and gNL(∂σ)4 independently from CMB observations.

    DOI: 10.1103/PhysRevD.91.123521

    Scopus

  50. Anisotropic CMB distortions from non-Gaussian isocurvature perturbations 査読有り

    Atsuhisa Ota, Toyokazu Sekiguchi, Yuichiro Tada, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 3 )   2014年12月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We calculate the CMB $\mu$-distortion and the angular power spectrum of its
    cross-correlation with the temperature anisotropy in the presence of the
    non-Gaussian neutrino isocurvature density (NID) mode. While the pure Gaussian
    NID perturbations give merely subdominant contribution to $<\mu>$ and vanishing
    $< \mu T>$, the latter quantity can be large enough to be detected in the
    future when the NID perturbations $\mathcal S(\mathbf x)$ are proportional to
    the square of a Gaussian field $g(\mathbf x)$, i.e. $\mathcal S({\mathbf
    x})\propto g^2({\mathbf x})$. In particular, large $< \mu T>$ can be realized
    since Gaussian-squared perturbations can yield a relatively large bispectrum,
    satisfying the constraints from the power spectrum of CMB anisotropies, i.e.
    $\mathcal{P}_\mathcal{SS}(k_0) \sim\mathcal{P}_g^2(k_0)\lesssim10^{-10}$ at
    $k_0=0.05$ Mpc$^{-1}$. We also forecast constraints from the CMB temperature
    and E-mode polarisation bispectra, and show that
    $\mathcal{P}_g(k_0)\lesssim10^{-5}$ would be allowed from Planck data. We find
    that $< \mu >$ and $|l(l+1)C^{\mu T}_l|$ can respectively be as large as
    $10^{-9}$ and $10^{-14}$ with uncorrelated scale-invariant NID perturbations
    for $\mathcal{P}_g(k_0)=10^{-5}$. When the spectrum of the Gaussian field is
    blue-tilted (with spectral index $n_g \simeq 1.5$), $< \mu T>$ can be enhanced
    by an order of magnitude.

    DOI: 10.1088/1475-7516/2015/03/013

    Web of Science

    arXiv

  51. Can a spectator scalar field enhance inflationary tensor mode? 査読有り

    Tomohiro Fujita, Jun'ichi Yokoyama, Shuichiro Yokoyama

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   ( 4 )   2014年11月

     詳細を見る

    記述言語:英語   出版者・発行元:OXFORD UNIV PRESS INC  

    We consider the possibility of enhancing the inflationary tensor mode by
    introducing a spectator scalar field with a small sound speed which induces
    gravitational waves as a second order effect. We analytically obtain the power
    spectra of gravitational waves and curvature perturbation induced by the
    spectator scalar field. We found that the small sound speed amplifies the
    curvature perturbation much more than the tensor mode and the current
    observational constraint forces the induced gravitational waves to be
    negligible compared with those from the vacuum fluctuation during inflation.

    DOI: 10.1093/ptep/ptv037

    Web of Science

    arXiv

    その他リンク: http://arxiv.org/pdf/1411.3658v1

  52. Probing small-scale cosmological fluctuations with the 21 cm forest: Effects of neutrino mass, running spectral index, and warm dark matter 査読有り

    Shimabukuro Hayato, Ichiki Kiyotomo, Inoue Susumu, Yokoyama Shuichiro

    PHYSICAL REVIEW D   90 巻 ( 8 )   2014年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Review D - Particles, Fields, Gravitation and Cosmology  

    Although the cosmological paradigm based on cold dark matter and adiabatic, nearly scale-invariant primordial fluctuations is consistent with a wide variety of existing observations, it has yet to be sufficiently tested on scales smaller than those of massive galaxies, and various alternatives have been proposed that differ significantly in the consequent small-scale power spectrum (SSPS) of large-scale structure. Here we show that a powerful probe of the SSPS at k≳10Mpc-1 can be provided by the 21 cm forest, that is, systems of narrow absorption lines due to intervening, cold neutral hydrogen in the spectra of high-redshift background radio sources in the cosmic reionization epoch. Such features are expected to be caused predominantly by collapsed gas in starless minihalos, whose mass function can be very sensitive to the SSPS. As specific examples, we consider the effects of neutrino mass, running spectral index (RSI) and warm dark matter (WDM) on the SSPS, and evaluate the expected distribution in optical depth of 21 cm absorbers out to different redshifts. Within the current constraints on quantities such as the sum of neutrino masses -mν, running of the primordial spectral index dns/dlnk and WDM particle mass mWDM, the statistics of the 21 cm forest manifest observationally significant differences that become larger at higher redshifts. In particular, it may be possible to probe the range of mWDM≳10keV that may otherwise be difficult to access. Future observations of the 21 cm forest by the Square Kilometer Array may offer a unique and valuable probe of the SSPS, as long as radio sources such as quasars or Population III gamma-ray bursts with sufficient brightness and number exist at redshifts of z≳10-20, and the astrophysical effects of reionization and heating can be discriminated.

    DOI: 10.1103/PhysRevD.90.083003

    Web of Science

    Scopus

    arXiv

  53. CDM/baryon isocurvature perturbations in a sneutrino curvaton model 査読有り

    Keisuke Harigaya, Taku Hayakawa, Masahiro Kawasaki, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 10 )   2014年9月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    Matter isocurvature perturbations are strictly constrained from cosmic
    microwave background observations. We study a sneutrino curvaton model where
    both cold dark matter (CDM)/baryon isocurvature perturbations are generated. In
    our model, total matter isocurvature perturbations are reduced since the
    CDM/baryon isocurvature perturbations compensate for each other. We show that
    this model can not only avoid the stringent observational constraints but also
    suppress temperature anisotropies on large scales, which leads to improved
    agreement with observations.

    DOI: 10.1088/1475-7516/2014/10/068

    Web of Science

    arXiv

    その他リンク: http://arxiv.org/pdf/1409.1669v1

  54. Thermal Effects and Sudden Decay Approximation in the Curvaton Scenario 査読有り

    Naoya Kitajima, David Langlois, Tomo Takahashi, Tomohiro Takesako, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 10 )   2014年7月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We study the impact of a temperature-dependent curvaton decay rate on the
    primordial curvature perturbation generated in the curvaton scenario. Using the
    familiar sudden decay approximation, we obtain an analytical expression for the
    curvature perturbation after the decay of the curvaton. We then investigate
    numerically the evolution of the background and of the perturbations during the
    decay. We first show that the instantaneous transfer coefficient, related to
    the curvaton energy fraction at the decay, can be extended into a more general
    parameter, which depends on the net transfer of the curvaton energy into
    radiation energy or, equivalently, on the total entropy ratio after the
    complete curvaton decay. We then compute the curvature perturbation and compare
    this result with the sudden decay approximation prediction.

    DOI: 10.1088/1475-7516/2014/10/032

    Web of Science

    arXiv

  55. Blue-tilted Tensor Spectrum and Thermal History of the Universe 査読有り

    Sachiko Kuroyanagi, Tomo Takahashi, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 2 )   2014年7月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We investigate constraints on the spectral index of primordial gravitational
    waves (GWs), paying particular attention to a blue-tilted spectrum. Such
    constraints can be used to test a certain class of models of the early
    Universe. We investigate observational bounds from LIGO+Virgo, pulsar timing
    and big bang nucleosynthesis, taking into account the suppression of the
    amplitude at high frequencies due to reheating after inflation and also
    late-time entropy production. Constraints on the spectral index are presented
    by changing values of parameters such as reheating temperatures and the amount
    of entropy produced at late time. We also consider constraints under the
    general modeling approach which can approximately describe various scenarios of
    the early Universe. We show that the constraints on the blue spectral tilt
    strongly depend on the underlying assumption and, in some cases, a highly
    blue-tilted spectrum can still be allowed.

    DOI: 10.1088/1475-7516/2015/02/003

    Web of Science

    arXiv

  56. Isocurvature perturbations and tensor mode in light of Planck and BICEP2 査読有り

    Masahiro Kawasaki, Toyokazu Sekiguchi, Tomo Takahashi, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 8 )   2014年4月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We investigate the degeneracy of the isocurvature perturbations and the
    primordial gravitational waves, by using recent observations of the cosmic
    microwave background (CMB) reported by Planck and BICEP2 collaborations. We
    show that the tension in the bound on the tensor-to-scalar ratio $r$ between
    Planck and BICEP2 can be resolved by introducing the anti-correlated
    isocurvature perturbations. Quantitatively, we find that with the
    anti-correlated isocurvature perturbations the constraints on $r$ from Planck
    alone and BICEP2 results can be consistent at 68 % C.L.

    DOI: 10.1088/1475-7516/2014/08/043

    Web of Science

    arXiv

  57. Curvaton in large field inflation 査読有り

    Tomohiro Fujita, Masahiro Kawasaki, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 9 )   2014年4月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We comprehensively explore the quadratic curvaton models in the chaotic
    inflation. In the light of the BICEP2 result $r \approx 0.2$, all model
    parameters and relevant observables are computed. It is found the curvaton
    field value is constrained into a narrow range, $\sigma_* =
    \mathcal{O}(10^{-2}$-$10^{-1})$ and the running of the spectral index is $n_s'
    \gtrsim -10^{-3}$. We show that if the curvaton is added, the models are
    heavily degenerated on the $n_s$ - $r$ plane. However, introducing a new plane,
    the degeneracy can be resolved. To distinguish the curvaton models, precise
    measurements of not only $r$ but also $n_s'$ and the tensor tilt $n_T$ are
    required.

    DOI: 10.1088/1475-7516/2014/09/015

    Web of Science

    arXiv

  58. Compensation for large tensor modes with iso-curvature perturbations in CMB anisotropies 査読有り

    Masahiro Kawasaki, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 5 )   2014年3月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    Recently, BICEP2 has reported the large tensor-to-scalar ratio
    $r=0.2^{+0.07}_{-0.05}$ from the observation of the cosmic microwave background
    (CMB) B-mode at degree-scales. Since tensor modes induce not only CMB B-mode
    but also the temperature fluctuations on large scales, to realize the
    consistent temperature fluctuations with the Planck result we should consider
    suppression of scalar perturbations on corresponding large scales. To realize
    such a suppression, we consider anti-correlated iso-curvature perturbations
    which could be realized in the simple curvaton model.

    DOI: 10.1088/1475-7516/2014/05/046

    Web of Science

    arXiv

  59. CMB distortion anisotropies due to the decay of primordial magnetic fields 査読有り

    Miyamoto Koichi, Sekiguchi Toyokazu, Tashiro Hiroyuki, Yokoyama Shuichiro

    PHYSICAL REVIEW D   89 巻 ( 6 )   2014年3月

     詳細を見る

    出版者・発行元:Physical Review D - Particles, Fields, Gravitation and Cosmology  

    DOI: 10.1103/PhysRevD.89.063508

    Web of Science

    Scopus

    arXiv

  60. Halo/galaxy bispectrum with primordial non-Gaussianity from integrated perturbation theory

    Yokoyama S.

    Physical Review D - Particles, Fields, Gravitation and Cosmology   89 巻 ( 4 )   2014年2月

     詳細を見る

    出版者・発行元:Physical Review D - Particles, Fields, Gravitation and Cosmology  

    DOI: 10.1103/PhysRevD.89.043524

    Scopus

  61. Halo/galaxy bispectrum with primordial non-Gaussianity from integrated perturbation theory

    Yokoyama Shuichiro, Matsubara Takahiko, Taruya Atsushi

    PHYSICAL REVIEW D   89 巻 ( 4 )   2014年2月

  62. Halo/galaxy bispectrum with primordial non-Gaussianity from integrated perturbation theory 査読有り

    Shuichiro Yokoyama, Takahiko Matsubara, Atsushi Taruya

    Physical Review D - Particles, Fields, Gravitation and Cosmology   89 巻 ( 4 )   2014年2月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    We derive a formula for the halo/galaxy bispectrum on the basis of the integrated perturbation theory (iPT). In addition to the gravity-induced non-Gaussianity, we consider the non-Gaussianity of the primordial curvature perturbations and investigate in detail the effect of such primordial non-Gaussianity on the large-scale halo/galaxy bispectrum. In iPT, the effects of primordial non-Gaussianity are wholly encapsulated in the linear (primordial) polyspectra, and we systematically calculate the contributions to the large-scale behaviors arising from the three types of primordial bispectrum (local, equilateral, and orthogonal types), and primordial trispectrum of the local-type non-Gaussianity. We find that the equilateral- and orthogonal-type non-Gaussianities show distinct scale-dependent behaviors which can dominate the gravity-induced non-Gaussianity at very large scales. For the local-type non-Gaussianity, higher-order loop corrections are found to give a significantly large contribution to the halo/galaxy bispectrum of the squeezed shape and eventually dominate over the other contributions on large scales. A diagrammatic approach based on the iPT helps us to systematically investigate an impact of such higher-order contributions to the large-scale halo/galaxy bispectrum. © 2014 American Physical Society.

    DOI: 10.1103/PhysRevD.89.043524

    Scopus

  63. Critical constraint on inflationary magnetogenesis 査読有り

    Tomohiro Fujita, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 3 )   2014年2月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    Recently, there are several reports that the cosmic magnetic fields on Mpc
    scale in void region is larger than $\sim 10^{-15}$G with an uncertainty of a
    few orders from the current blazar observations. On the other hand, in
    inflationary magnetogenesis models, additional primordial curvature
    perturbations are inevitably produced from iso-curvature perturbations due to
    generated electromagnetic fields. We explore such induced curvature
    perturbations in a model independent way and obtained a severe upper bound for
    the energy scale of inflation from the observed cosmic magnetic fields and the
    observed amplitude of the curvature perturbation, as $\rho_{\rm inf}^{1/4} <
    30{\rm GeV} \times (B_{\rm obs}/10^{-15}{\rm G})^{-1}$ where $B_{\rm obs}$ is
    the strength of the magnetic field at present. Therefore, without a dedicated
    low energy inflation model or an additional amplification of magnetic fields
    after inflation, inflationary magnetogenesis on Mpc scale is generally
    incompatible with CMB observations.

    DOI: 10.1088/1475-7516/2014/03/013

    Web of Science

    arXiv

  64. Dark energy from inflation 査読有り

    Ringeval Christophe, Suyama Teruaki, Takahashi Tomo, Yamaguchi Masahide, Yokoyama Shuichiro

    PASCOS 2012 - 18TH INTERNATIONAL SYMPOSIUM ON PARTICLES STRINGS AND COSMOLOGY   485 巻 ( 1 )   2014年

     詳細を見る

    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Journal of Physics: Conference Series  

    DOI: 10.1088/1742-6596/485/1/012023

    Web of Science

    Scopus

  65. Erratum: Critical constraint on inflationary magnetogenesis (Journal of Cosmology and Astroparticle Physics (2014) (013)) 査読有り

    Tomohiro Fujita, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2014 巻 ( 5 )   2014年

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Institute of Physics Publishing  

    DOI: 10.1088/1475-7516/2014/05/E02

    Scopus

  66. Halo/Galaxy Bispectrum with Primordial non-Gaussianity from integrated Perturbation Theory (iPT) 査読有り

    Shuichiro Yokoyama, Takahiko Matsubara, Atsushi Taruya

    PHYSICAL REVIEW D   89 巻 ( 4 )   2013年10月

     詳細を見る

    記述言語:英語   出版者・発行元:AMER PHYSICAL SOC  

    We derive a formula for the halo/galaxy bispectrum on the basis of the
    integrated Perturbation Theory (iPT). In addition to the gravity-induced
    non-Gaussianity, we consider the non-Gaussianity of the primordial curvature
    perturbations, and investigate in detail the effect of such primordial
    non-Gaussianity on the large-scale halo/galaxy bispectrum. In iPT, the effects
    of primordial non-Gaussianity are wholly encapsulated in the linear
    (primordial) polyspectra, and we systematically calculate the contributions to
    the large-scale behaviors arising from the three types of primordial bispectrum
    (local-, equilateral-, and orthogonal-types), and primordial trispectrum of the
    local-type non-Gaussianity. We find that the equilateral- and orthogonal-type
    non-Gaussianities show distinct scale-dependent behaviors which can dominate
    the gravity-induced non-Gaussianity at very large scales. For the local-type
    non-Gaussianity, higher-order loop corrections are found to give a
    significantly large contribution to the halo/galaxy bispectrum of the squeezed
    shape, and eventually dominate over the other contributions on large scales. A
    diagrammatic approach based on the iPT helps us to systematically investigate
    an impact of such higher-order contributions to the large-scale halo/galaxy
    bispectrum.

    DOI: 10.1103/PhysRevD.89.043524

    Web of Science

    arXiv

  67. Higher order statistics of curvature perturbations in IFF model and its Planck constraints 査読有り

    Tomohiro Fujita, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2013 巻 ( 9 )   2013年9月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    We compute the power spectrum ζ and non-linear parameters fNL and τNL of the curvature perturbation induced during inflation by the electromagnetic fields in the kinetic coupling model (IFF model). By using the observational result of ζ,fNL and τNL reported by the Planck collaboration, we study the constraint on the model comprehensively. Interestingly, if the single slow-rolling inflaton is responsible for the observed ζ, the constraint from τNL is most stringent. We also find a general relationship between fNL and τNL generated in this model. Even if fNL ∼ (1), a detectable τNL can be produced. © 2013 IOP Publishing Ltd and Sissa Medialab srl.

    DOI: 10.1088/1475-7516/2013/09/009

    Scopus

    arXiv

  68. Scale-dependent bias due to primordial vector fields 査読有り

    Shiraishi Maresuke, Yokoyama Shuichiro, Ichiki Kiyotomo, Matsubara Takahiko

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   432 巻 ( 3 ) 頁: 2331 - 2338   2013年7月

     詳細を見る

    出版者・発行元:Monthly Notices of the Royal Astronomical Society  

    Anisotropic stress perturbations induced by primordial Gaussian vector fields create non- Gaussianity in curvature perturbations.We found that such non-Gaussianity closely resembles the local-type non-Gaussianity parametrized by fNL, and generates scale-dependent bias in large-scale structures. We also found a simple relationship between the scale-dependent bias and the power spectrum of the vector fields.When the vector fields are interpreted as primordial magnetic fields, the effective fNL is shown to be always negative. The scale-dependent bias provides a new approach to probing primordial vector fields. © 2013 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.

    DOI: 10.1093/mnras/stt594

    Web of Science

    Scopus

    arXiv

  69. Gravitational waves from a curvaton model with blue spectrum 査読有り

    Masahiro Kawasaki, Naoya Kitajima, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 8 )   2013年5月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We investigate the gravitational wave background induced by the first order
    scalar perturbations in the curvaton models. We consider the quadratic and
    axion-like curvaton potential which can generate the blue-tilted power spectrum
    of curvature perturbations on small scales and derive the maximal amount of
    gravitational wave background today. We find the power spectrum of the induced
    gravitational wave background has a characteristic peak at the frequency
    corresponding to the scale reentering the horizon at the curvaton decay, in the
    case where the curvaton does not dominate the energy density of the Universe.
    We also find the enhancement of the amount of the gravitational waves in the
    case where the curvaton dominates the energy density of the Universe. Such
    induced gravitational waves would be detectable by the future space-based
    gravitational wave detectors or pulsar timing observations.

    DOI: 10.1088/1475-7516/2013/08/042

    Web of Science

    arXiv

  70. Full bispectra from primordial scalar and tensor perturbations in the most general single-field inflation model 査読有り

    Gao Xian, Kobayashi Tsutomu, Shiraishi Maresuke, Yamaguchi Masahide, Yokoyama Jun'ichi, Yokoyama Shuichiro

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   2013 巻 ( 5 )   2013年5月

     詳細を見る

    出版者・発行元:Progress of Theoretical and Experimental Physics  

    DOI: 10.1093/ptep/ptt031

    Web of Science

    Scopus

    arXiv

  71. Implications of Planck results for models with local type non-Gaussianity 査読有り

    Teruaki Suyama, Tomo Takahashi, Masahide Yamaguchi, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 6 )   2013年3月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We discuss implications of Planck results for models with local type
    non-Gaussianity. In light of the recent results of the Planck satellite, we
    constrain model parameters of several representative models and give the
    prediction of trispectrum, in particular, gNL. We also consider interesting
    possibilities that trispectrum appears as the first signature of the
    non-Gaussianities of the curvature perturbations, that is, fNL is small while
    gNL can be significantly large.

    DOI: 10.1088/1475-7516/2013/06/012

    Web of Science

    arXiv

    その他リンク: http://arxiv.org/pdf/1303.5374v3

  72. Statistics of general functions of a Gaussian field -application to non-Gaussianity from preheating- 査読有り

    Teruaki Suyama, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 6 )   2013年3月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We provide a general formula for calculating correlators of arbitrary
    function of a Gaussian field. This work extends the standard leading-order
    approximation based on the delta N formalism to the case where truncation of
    the delta N at some low order does not yield the correct answer. As an
    application of this formula, we investigate 2, 3 and 4-point functions of the
    primordial curvature perturbation generated in the massless preheating model by
    approximating the mapping between the curvature perturbation and the Gaussian
    field as a sum of the many spiky normal distribution functions as suggested by
    lattice calculations. We also discuss observational consequences of this case
    and show that trispectrum would be a key observable to search signature of
    preheating in the CMB map. It is found the forms of the curvature correlation
    functions for any delta N, at the leading order in the correlator of the
    Gaussian field, coincide with the standard local type ones. Within this
    approximation, it is also found that the standard formula for the non-linearity
    parameters given by the product of the derivatives of the e-folding number
    still holds after we replace the bare e-folding number appearing in the
    original delta N expansion with the one smoothed in the field space with a
    Gaussian window function.

    DOI: 10.1088/1475-7516/2013/06/018

    Web of Science

    arXiv

  73. Scale-dependent bias with higher order primordial non-Gaussianity: Use of the integrated perturbation theory 査読有り

    Yokoyama Shuichiro, Matsubara Takahiko

    PHYSICAL REVIEW D   87 巻 ( 2 )   2013年1月

     詳細を見る

    記述言語:英語   出版者・発行元:Physical Review D - Particles, Fields, Gravitation and Cosmology  

    We analytically derive a more accurate formula for the power spectrum of the biased objects with the primordial non-Gaussianity parametrized not only by the nonlinearity parameter fNL, but also by gNL and τNL which characterize the trispectrum of the primordial curvature perturbations. We adopt the integrated perturbation theory which was constructed in Matsubara. We discuss an inequality between fNL and τNL in the context of the scale-dependent bias, by introducing a stochasticity parameter. We also mention higher order loop corrections in the scale dependency of the bias parameter. © 2013 American Physical Society.

    DOI: 10.1103/PhysRevD.87.023525

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/1210.2495v1

  74. CMB power spectra induced by primordial cross-bispectra between metric perturbations and vector fields 査読有り

    Shiraishi Maresuke, Saga Shohei, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2012 巻 ( 11 )   2012年11月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2012/11/046

    Web of Science

    Scopus

    arXiv

  75. Optimal limits on primordial magnetic fields from CMB temperature bispectrum of passive modes 査読有り

    Shiraishi Maresuke, Nitta Daisuke, Yokoyama Shuichiro, Ichiki Kiyotomo

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2012 巻 ( 3 )   2012年3月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    We investigate bounds on the strength of the primordial magnetic field (PMF) from the cosmic microwave background (CMB) bispectra of the intensity (temperature) modes induced from the auto- and cross-correlated bispectra of the scalar and tensor components of the PMF anisotropic stress. At first, we construct a general formula for the CMB intensity and polarization bispectra from PMFs composed of any type of perturbation. Then we derive an approximate expression which traces the exact shape of the CMB bispectrum in order to reduce the computation time with respect to a large number of the multipole configurations, and also show that the non-Gaussian structure coming from PMFs is classified as the local-type configuration. Computing the signal-to-noise ratio on the basis of the approximate formula with the information of the instrumental noises and resolutions, we find expected upper bounds on the magnetic field strength, when the magnetic spectrum is nearly scale invariant (nB = -2.9), smoothed on 1Mpc scale at 95% confidence level from the WMAP and PLANCK experiments as B1Mpc < 4.0-6.7nG and 3.8-6.5nG, respectively, depending on the energy scale of the magnetic field production from 1014GeV to 103GeV. Our new consequences imply slight overestimations by the previous rough discussions.©2012 IOP Publishing Ltd and Sissa Medialab srl.

    DOI: 10.1088/1475-7516/2012/03/041

    Web of Science

    Scopus

    arXiv

  76. Testing the origin of primordial perturbation: Use of bi and tri-spectrum 査読有り

    T. Suyama, K. Ichikawa, M. Kawasaki, K. Nakayama, T. Sekiguchi, F. Takahashi, T. Takahashi, T. Tanaka, Y. Watanabe, M. Yamaguchi, J. Yokoyama, S. Yokoyama

    RESCEU Symposium on General Relativity and Gravitation, JGRG 22     頁: 111303-   2012年

     詳細を見る

    記述言語:英語  

  77. Use of σ N formalism-difficulty of generating large local-type non-gaussianity during inflation

    Tanaka T., Suyama T., Yokoyama S.

    Progress of Theoretical Physics Supplement   ( 190 ) 頁: 135 - 142   2011年12月

     詳細を見る

    出版者・発行元:Progress of Theoretical Physics Supplement  

    We discuss generation of non-Gaussianity in primordial density perturbation through the super-horizon evolution during inflation by using the so-called δN formalism. In order to discuss the difficulties of generating large local-type non-Gaussianity during inflation, we discuss Kadota-Stewart model. This model gives an example in which we have to choose rather unnatural initial conditions even if large non-Gaussianity can be generated.

    Scopus

  78. Fine features in the primordial power spectrum 査読有り

    Kumazaki Kohei, Yokoyama Shuichiro, Sugiyama Naoshi

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2011 巻 ( 12 )   2011年12月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2011/12/008

    Web of Science

    Scopus

    arXiv

  79. Scale-dependent bias from the primordial non-Gaussianity with a Gaussian-squared field 査読有り

    Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2011 巻 ( 11 )   2011年11月

     詳細を見る

    記述言語:英語   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    We investigate the halo bias in the case where the primordial curvature fluctuations, Φ, are sourced from both a Gaussian random field and a Gaussian-squared field, as Φ(x) = φ(x)+ψ(x)2-ψ(x) 2ngle, so-called "ungaussiton model". We employ the peak-background split formula and find a new scale-dependence in the halo bias induced from the Gaussian-squared field. © 2011 IOP Publishing Ltd and SISSA.

    DOI: 10.1088/1475-7516/2011/11/001

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/1108.5569v1

  80. Violation of the Rotational Invariance in the CMB Bispectrum

    Shiraishi Maresuke, Yokoyama Shuichiro

    PROGRESS OF THEORETICAL PHYSICS   126 巻 ( 5 ) 頁: 923 - 935   2011年11月

     詳細を見る

  81. Parity Violation of Gravitons in the CMB Bispectrum

    Shiraishi Maresuke, Nitta Daisuke, Yokoyama Shuichiro

    PROGRESS OF THEORETICAL PHYSICS   126 巻 ( 5 ) 頁: 937 - 959   2011年11月

     詳細を見る

  82. Parity violation of gravitons in the CMB bispectrum 査読有り

    Shiraishi M.

    Progress of Theoretical Physics   126 巻 ( 5 ) 頁: 937 - 959   2011年11月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Progress of Theoretical Physics  

    We investigate the cosmic microwave background (CMB) bispectra of the intensity (temperature) and polarization modes induced by the graviton non-Gaussianities, which arise from the parity-conserving and parity-violating Weyl cubic terms with time-dependent coupling. By considering the time-dependent coupling, we find that even in the exact de Sitter space time, the parity violation still appears in the three-point function of the primordial gravitational waves and could become large. Through the estimation of the CMB bispectra, we demonstrate that the signals generated from the parity-conserving and parity-violating terms appear in completely different configurations of multipoles. For example, the parity-conserving non-Gaussianity induces the nonzero CMB temperature bispectrum in the configuration with Σ_<n=1>^3l_n=even and, while due to the parity-violating non-Gaussianity, the CMB temperature bispectrum also appears for Σ_<n=1>^3l_n=odd. This signal is just good evidence of the parity violation in the non-Gaussianity of primordial gravitational waves. We find that the shape of this non-Gaussianity is similar to the so-called equilateral one and the amplitudes of these spectra at large scale are roughly estimated as |b_<lll>|~l^<-4>×3.2×10^<-2>(GeV/Λ)^2 (r/0.1)^4, where Λ is an energy scale that sets the magnitude of the Weyl cubic terms (higher derivative corrections) and r is a tensor-to-scalar ratio. Taking the limit for the nonlinearity parameter of the equilateral type as f_<NL>^<eq><300, we can obtain a bound as Λ&gsum;3×10^6GeV, assuming r=0.1.

    DOI: 10.1143/PTP.126.937

    Scopus

    arXiv

  83. Use of δN Formalism : Difficulty of Generating Large Local-Type Non-Gaussianity during Inflation

    Tanaka Takahiro, Suyama Teruaki, Yokoyama Shuichiro

    Progress of theoretical physics. Supplement   ( 190 ) 頁: 135 - 142   2011年10月

     詳細を見る

    出版者・発行元:Publication Office, Progress of Theoretical Physics  

    We discuss generation of non-Gaussianity in primordial density perturbation through the super-horizon evolution during inflation by using the so-called δN formalism. In order to discuss the difficulties of generating large local-type non-Gaussianity during inflation, we discuss Kadota-Stewart model. This model gives an example in which we have to choose rather unnatural initial conditions even if large non-Gaussianity can be generated.

    DOI: 10.1143/PTPS.190.135

  84. Scale-dependent bias from primordial non-Gaussianity with trispectrum 査読有り

    Gong Jinn-Ouk, Yokoyama Shuichiro

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   417 巻 ( 1 ) 頁: L79 - L82   2011年10月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Monthly Notices of the Royal Astronomical Society: Letters  

    We study the scale-dependent bias of the halo power spectrum arising from primordial non-Gaussianity. We present an analytic result of the halo bias including up to the trispectrum contributions. We find that the scale-dependent bias opens a new possibility of probing the relation between the non-linearity parametersfNL and τNL. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

    DOI: 10.1111/j.1745-3933.2011.01124.x

    Web of Science

    Scopus

  85. Modification of the halo mass function by kurtosis associated with primordial non-Gaussianity 査読有り

    Yokoyama Shuichiro, Sugiyama Naoshi, Zaroubi Saleem, Silk Joseph

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   417 巻 ( 2 ) 頁: 1074 - 1087   2011年10月

     詳細を見る

    出版者・発行元:Monthly Notices of the Royal Astronomical Society  

    DOI: 10.1111/j.1365-2966.2011.19323.x

    Web of Science

    Scopus

    arXiv

  86. Violation of the rotational invariance in the CMB bispectrum 査読有り

    Shiraishi M.

    Progress of Theoretical Physics   126 巻 ( 5 ) 頁: 923 - 935   2011年7月

     詳細を見る

    出版者・発行元:Progress of Theoretical Physics  

    We investigate a statistical anisotropy on the Cosmic Microwave Background (CMB) bispectrum, which can be generated from the primordial non-Gaussianity induced by quantum fluctuations of a vector field. We find new configurations in the multipole space of the CMB bispectrum given by l_1=l_2+l_3+2,|l_2-l_3|-2 and their permutations, which violate the rotational invariance, such as an off-diagonal configuration in the CMB power spectrum. We also find that in a model presented by Yokoyama and Soda (2008), the amplitude of the statistically anisotropic bispectrum in the above configurations becomes as large as that in other configurations such as l_1=l_2+l_3. As a result, it might be possible to detect these contributions in future experiments, which would give us novel information about the physics of the early Universe.

    DOI: 10.1143/PTP.126.923

    Web of Science

    Scopus

    arXiv

  87. Extension of local-type inequality for the higher order correlation functions 査読有り

    Suyama Teruaki, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2011 巻 ( 7 )   2011年7月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2011/07/033

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/1105.5851v2

  88. Computation approach for CMB bispectrum from primordial magnetic fields 査読有り

    Shiraishi Maresuke, Nitta Daisuke, Yokoyama Shuichiro, Ichiki Kiyotomo, Takahashi Keitaro

    PHYSICAL REVIEW D   83 巻 ( 12 )   2011年6月

     詳細を見る

    出版者・発行元:Physical Review D - Particles, Fields, Gravitation and Cosmology  

    DOI: 10.1103/PhysRevD.83.123523

    Web of Science

    Scopus

    arXiv

  89. Cosmic microwave background bispectrum of tensor passive modes induced from primordial magnetic fields 査読有り

    Shiraishi Maresuke, Nitta Daisuke, Yokoyama Shuichiro, Ichiki Kiyotomo, Takahashi Keitaro

    PHYSICAL REVIEW D   83 巻 ( 12 )   2011年6月

     詳細を見る

    掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Review D - Particles, Fields, Gravitation and Cosmology  

    DOI: 10.1103/PhysRevD.83.123003

    Web of Science

    Scopus

    arXiv

  90. CMB Bispectrum from Primordial Scalar, Vector and Tensor Non-Gaussianities

    Shiraishi Maresuke, Nitta Daisuke, Yokoyama Shuichiro, Ichiki Kiyotomo, Takahashi Keitaro

    PROGRESS OF THEORETICAL PHYSICS   125 巻 ( 4 ) 頁: 795 - 813   2011年4月

     詳細を見る

  91. Affleck-Dine baryogenesis with modulated reheating 査読有り

    Kamada Kohei, Kohri Kazunori, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2011 巻 ( 1 )   2011年1月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2011/01/027

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/1008.1450v2

  92. Use of delta N Formalism - Difficulty of Generating Large Local-Type Non-Gaussianity during Inflation

    Tanaka Takahiro, Suyama Teruaki, Yokoyama Shuichiro

    PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT   ( 190 ) 頁: 135 - 142   2011年

     詳細を見る

  93. Cosmic microwave background bispectrum of vector modes induced from primordial magnetic fields (vol 82, 121302, 2010) 査読有り

    Shiraishi, Maresuke, Nitta, Daisuke, Yokoyama, Shuichiro, Ichiki, Kiyotomo, Takahashi, Keitaro

    Physical Review D   83 巻 ( 2 )   2011年

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1103/PHYSREVD.83.029901

    Web of Science

  94. Use of σ N formalism-difficulty of generating large local-type non-gaussianity during inflation 査読有り

    T. Tanaka, T. Suyama, S. Yokoyama

    Progress of Theoretical Physics Supplement   ( 190 ) 頁: 135 - 142   2011年

     詳細を見る

    記述言語:英語  

  95. Cosmic microwave background bispectrum of vector modes induced from primordial magnetic fields

    Shiraishi Maresuke, Nitta Daisuke, Yokoyama Shuichiro, Ichiki Kiyotomo, Takahashi Keitaro

    PHYSICAL REVIEW D   82 巻 ( 12 )   2010年12月

     詳細を見る

    出版者・発行元:Physical Review D - Particles, Fields, Gravitation and Cosmology  

    DOI: 10.1103/PhysRevD.82.121302

    Web of Science

    Scopus

  96. CMB bispectrum from primordial scalar, vector and tensor non-gaussianities 査読有り

    Shiraishi M.

    Progress of Theoretical Physics   125 巻 ( 4 ) 頁: 795 - 813   2010年12月

     詳細を見る

    出版者・発行元:Progress of Theoretical Physics  

    We present an all-sky formalism for the Cosmic Microwave Background (CMB) bispectrum induced by the primordial non-Gaussianities not only in scalar but also in vector and tensor fluctuations. We find that the bispectrum can be formed in an explicitly rationally invariant way by taking into account the angular and polarization dependences of the vector and tensor modes. To demonstrate this and present how to use our formalism, we consider a specific example of the correlation between two scalars and a graviton as the source of non-Gaussianity. As a result, we show that the CMB reduced bispectrum of the intensity anisotropies is evaluated as a function of the multipole and the coupling constant between two scalars and a graviton denoted by g_<tss>; |b_<lll>|~l^<-4>×8×10^<-18>|g_<tss>|. By estimating the signal-to-noise ratio, we find that the constraint as |g_<tss>|<6 will be expected from the PLANCK experiment.

    DOI: 10.1143/PTP.125.795

    Web of Science

    Scopus

    arXiv

  97. The CMB bispectrum from vector-mode perturbations induced by primordial magnetic fields

    Shiraishi M.

    Proceedings of the 20th Workshop on General Relativity and Gravitation in Japan, JGRG 2010     頁: 367 - 370   2010年12月

     詳細を見る

    出版者・発行元:Proceedings of the 20th Workshop on General Relativity and Gravitation in Japan, JGRG 2010  

    Scopus

  98. Iso-curvature fluctuations in modulated reheating scenario

    Yokoyama S.

    Proceedings of the 20th Workshop on General Relativity and Gravitation in Japan, JGRG 2010     頁: 456 - 459   2010年12月

     詳細を見る

    出版者・発行元:Proceedings of the 20th Workshop on General Relativity and Gravitation in Japan, JGRG 2010  

    Scopus

  99. On classification of models of large local-type non-Gaussianity 査読有り

    Suyama Teruaki, Takahashi Tomo, Yamaguchi Masahide, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2010 巻 ( 12 )   2010年12月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2010/12/030

    Web of Science

    Scopus

    arXiv

  100. Analytic formulae of the CMB bispectra generated from non-Gaussianity in the tensor and vector perturbations 査読有り

    Shiraishi Maresuke, Yokoyama Shuichiro, Nitta Daisuke, Ichiki Kiyotomo, Takahashi Keitaro

    PHYSICAL REVIEW D   82 巻 ( 10 )   2010年11月

     詳細を見る

    出版者・発行元:Physical Review D - Particles, Fields, Gravitation and Cosmology  

    DOI: 10.1103/PhysRevD.82.103505

    Web of Science

    Scopus

    arXiv

  101. Dark Energy from Primordial Inflationary Quantum Fluctuations 査読有り

    Ringeval Christophe, Suyama Teruaki, Takahashi Tomo, Yamaguchi Masahide, Yokoyama Shuichiro

    PHYSICAL REVIEW LETTERS   105 巻 ( 12 ) 頁: 121301   2010年9月

     詳細を見る

    出版者・発行元:Physical Review Letters  

    DOI: 10.1103/PhysRevLett.105.121301

    Web of Science

    Scopus

    PubMed

    arXiv

  102. Use of delta N formalism-difficulties in generating large local-type non-Gaussianity during inflation 査読有り

    Tanaka Takahiro, Suyama Teruaki, Yokoyama Shuichiro

    CLASSICAL AND QUANTUM GRAVITY   27 巻 ( 12 )   2010年6月

  103. Ghost dark matter 査読有り

    Furukawa Tomonori, Yokoyama Shuichiro, Ichiki Kiyotomo, Sugiyama Naoshi, Mukohyama Shinji

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2010 巻 ( 5 )   2010年5月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2010/05/007

    Web of Science

    Scopus

    arXiv

  104. Relation between inflation and dark energy

    Ringeval Christophe, Suyama Teruaki, Takahashi Tomo, Yamaguchi Masahide, Yokoyama Shuichiro

    16TH INTERNATIONAL SYMPOSIUM ON PARTICLES, STRINGS AND COSMOLOGY (PASCOS 2010)   259 巻 ( 1 )   2010年

     詳細を見る

    記述言語:英語   出版者・発行元:Journal of Physics: Conference Series  

    In this talk, we have shown that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale. © 2010 IOP Publishing Ltd.

    DOI: 10.1088/1742-6596/259/1/012082

    Web of Science

    Scopus

  105. The CMB bispectrum from vector-mode perturbations induced by primordial magnetic fields 査読有り

    Maresuke Shiraishi, Daisuke Nitta, Shuichiro Yokoyama, Kiyotomo Ichiki, Keitaro Takahashi

    Proceedings of the 20th Workshop on General Relativity and Gravitation in Japan, JGRG 2010     頁: 367 - 370   2010年

     詳細を見る

    掲載種別:研究論文(国際会議プロシーディングス)  

    We calculate CMB bispectrum of vector modes induced from primordial magnetic fields. We take into account the full angular dependence of the bispectrum and discuss the amplitude and also the shape of the bispectrum. In the squeezed limit, we estimate a typical values of the normalized reduced bispectrum as ℓ11(ℓ1+1) ℓ3(ℓ 3+1) |bℓ1ℓ2ℓ3|∼2 × 10 -19, for the strength of the primordial magnetic field smoothed on 1Mpc scale B1Mpc = 4.7nG assuming nearly scale-invariant spectrum of magnetic fields. We find that a new constraint on the magnetic field strength will be placed as B1Mpc < 10nG if PLANCK will place a limit on the nonlinearity parameter of local-type configuration as |flocalNL | < 5.

    Scopus

  106. Density fluctuations in thermal inflation and non-gaussianity

    Yokoyama S.

    Proceedings of the 19th Workshop on General Relativity and Gravitation in Japan, JGRG 2009     頁: 397 - 400   2009年12月

     詳細を見る

    出版者・発行元:Proceedings of the 19th Workshop on General Relativity and Gravitation in Japan, JGRG 2009  

    Scopus

  107. Density fluctuations in thermal inflation and non-Gaussianity 査読有り

    Kawasaki Masahiro, Takahashi Tomo, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2009 巻 ( 12 )   2009年12月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2009/12/012

    Web of Science

    Scopus

    arXiv

  108. Primordial non-Gaussianity in models with dark matter isocurvature fluctuations 査読有り

    Takahashi Tomo, Yamaguchi Masahide, Yokoyama Shuichiro

    PHYSICAL REVIEW D   80 巻 ( 6 )   2009年9月

     詳細を見る

    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Physical Review D - Particles, Fields, Gravitation and Cosmology  

    We investigate primordial non-Gaussianity and dark matter isocurvature fluctuations in the modulated reheating and the curvaton scenarios. In these scenarios, a large non-Gaussianity can be generated; on the other hand, depending on how dark matter is produced, too large isocurvature fluctuations can also arise, which is inconsistent with current observations. In this paper, we study this issue in a mixed scenario where the curvature fluctuations can also be produced from the inflaton fluctuations as well as those from a light scalar field such as the modulus and the curvaton. We show that primordial fluctuations can be highly non-Gaussian without conflicting with the current constraint on isocurvature fluctuations for such mixed scenarios. However, if the constraint on isocurvature fluctuations becomes severer as expected by the Planck satellite, fNL, a nonlinearity parameter for adiabatic fluctuations, should be very small as fNL3, which would give interesting implications for the generation mechanism of dark matter. Non-Gaussianity from isocurvature fluctuations is also discussed in these scenarios. © 2009 The American Physical Society.

    DOI: 10.1103/PhysRevD.80.063524

    Web of Science

    Scopus

  109. Phenomenological aspects of Horava-Lifshitz cosmology 査読有り

    Mukohyama Shinji, Nakayama Kazunori, Takahashi Fuminobu, Yokoyama Shuichiro

    PHYSICS LETTERS B   679 巻 ( 1 ) 頁: 6 - 9   2009年8月

     詳細を見る

    記述言語:英語   出版者・発行元:Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics  

    We show that, assuming the dispersion relation proposed recently by Hořava in the context of quantum gravity, radiation energy density exhibits a peculiar dependence on the scale factor; the radiation energy density decreases proportional to a-6. This simple scaling can have an impact on cosmology. As an example, we show that the resultant baryon asymmetry as well as the stochastic gravity waves can be enhanced. We also discuss current observational constraint on the dispersion relation. © 2009 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physletb.2009.07.005

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/0905.0055v2

  110. Gravitino dark matter and non-Gaussianity 査読有り

    Takahashi Tomo, Yamaguchi Masahide, Yokoyama Jun'ichi, Yokoyama Shuichiro

    PHYSICS LETTERS B   678 巻 ( 1 ) 頁: 15 - 19   2009年7月

     詳細を見る

    出版者・発行元:Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics  

    DOI: 10.1016/j.physletb.2009.06.007

    Web of Science

    Scopus

    arXiv

    その他リンク: http://arxiv.org/pdf/0905.0240v2

  111. Gravitational waves from p-form inflation 査読有り

    Kobayashi Tsutomu, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2009 巻 ( 5 )   2009年5月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2009/05/004

    Web of Science

    Scopus

    arXiv

  112. Efficient diagrammatic computation method for higher order correlation functions of local type primordial curvature perturbations 査読有り

    Yokoyama Shuichiro, Suyama Teruaki, Tanaka Takahiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2009 巻 ( 2 )   2009年2月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2009/02/012

    Web of Science

    Scopus

    arXiv

  113. Anisotropic inflation from vector impurity

    Kimura M.

    Proceedings of the 18th Workshop on General Relativity and Gravitation in Japan, JGRG 2008     2008年12月

     詳細を見る

    出版者・発行元:Proceedings of the 18th Workshop on General Relativity and Gravitation in Japan, JGRG 2008  

    Scopus

  114. Anisotropic inflation from vector impurity 査読有り

    Kanno Sugumi, Kimura Masashi, Soda Jiro, Yokoyama Shuichiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2008 巻 ( 8 )   2008年8月

     詳細を見る

    出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    DOI: 10.1088/1475-7516/2008/08/034

    Web of Science

    Scopus

    arXiv

  115. Primordial statistical anisotropy generated at the end of inflation 査読有り

    Yokoyama Shuichiro, Soda Jiro

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   2008 巻 ( 8 )   2008年8月

     詳細を見る

    記述言語:英語   出版者・発行元:Journal of Cosmology and Astroparticle Physics  

    We present a new mechanism for generating primordial statistical anisotropy of curvature perturbations. We introduce a vector field which has a non-minimal kinetic term and couples with a waterfall field in a hybrid inflation model. In such a system, the vector field gives fluctuations of the end of inflation and hence induces a subcomponent of curvature perturbations. Since the vector has a preferred direction, the statistical anisotropy could appear in the fluctuations. We present the explicit formula for the statistical anisotropy in the primordial power spectrum and the bispectrum of curvature perturbations. Interestingly, there is the possibility that the statistical anisotropy does not appear in the power spectrum but does appear in the bispectrum. We also find that the statistical anisotropy provides the shape dependence to the bispectrum. © 2008 IOP Publishing Ltd. and SISSA.

    DOI: 10.1088/1475-7516/2008/08/005

    Web of Science

    Scopus

    arXiv

  116. Primordial Non-Gaussianity in Multi-Scalar Inflation 査読有り

    Shuichiro Yokoyama, Teruaki Suyama, Takahiro Tanaka

    PHYSICAL REVIEW D   77 巻 ( 8 )   2007年11月

     詳細を見る

    記述言語:英語   出版者・発行元:AMER PHYSICAL SOC  

    We give a concise formula for the non-Gaussianity of the primordial curvature
    perturbation generated on super-horizon scales in multi-scalar inflation model
    without assuming slow-roll conditions. This is an extension of our previous
    work. Using this formula, we study the generation of non-Gaussianity for the
    double inflation models in which the slow-roll conditions are temporarily
    violated after horizon exit, and we show that the non-linear parameter $f_{NL}$
    for such models is suppressed by the slow-roll parameters evaluated at the time
    of horizon exit.

    DOI: 10.1103/PhysRevD.77.083511

    Web of Science

    arXiv

    その他リンク: http://arxiv.org/pdf/0711.2920v3

  117. Primordial Non-Gaussianity in Multi-Scalar Slow-Roll Inflation 査読有り

    Shuichiro Yokoyama, Teruaki Suyama, Takahiro Tanaka

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 7 )   2007年5月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We analyze the non-Gaussianity for primordial curvature perturbations
    generated in multi-scalar slow-roll inflation model including the model with
    non-separable potential by making use of $\delta N$ formalism. Many authors
    have investigated the possibility of large non-Gaussianity for the models with
    separable potential, and they have found that the non-linear parameter,
    $f_{NL}$, is suppressed by the slow-roll parameters. We show that for the
    non-separable models $f_{NL}$ is given by the product of a factor which is
    suppressed by the slow-roll parameters and a possible enhancement factor which
    is given by exponentials of quantities of O(1).

    DOI: 10.1088/1475-7516/2007/07/013

    Web of Science

    arXiv

    その他リンク: http://arxiv.org/pdf/0705.3178v1

  118. Primordial non-Gaussianity generated during inflation 査読有り

    S. Yokoyama, T. Suyama, T. Tanaka

    Proceedings of the 17th Workshop on General Relativity and Gravitation in Japan, JGRG 2007     頁: 177 - 180   2007年

     詳細を見る

    記述言語:英語  

  119. Generating the primordial curvature perturbations in preheating 査読有り

    Teruaki Suyama, Shuichiro Yokoyama

    Class.Quant.Grav.24:1615-1626,2007     2006年6月

     詳細を見る

    We show that the primordial curvature perturbations may originate not from
    the quantum fluctuations of inflaton during inflation but from isocurvature
    perturbations which are amplified during preheating after inflation. We
    consider a simple preheating model, whose potential is given by $V(\phi,
    \chi)={1/4}\lambda \phi^4+{1/2}g^2 \phi^2 \chi^2$ with $g^2/\lambda=2$, as a
    possible realization of generating curvature perturbations during preheating.
    We make use of the $\delta N$ formalism which requires only knowledge of the
    homogeneous background solutions in order to evaluate the evolution of
    curvature perturbations on super-horizon scales. We solve the background
    equations numerically and find that the amplitude and the spectral index of
    curvature perturbations originating from preheating can be tuned to the
    observed values if the isocurvature perturbations at the end of inflation is
    not suppressed on super-horizon scales. We also point out that the tensor to
    scalar ratio in ${1/4}\lambda \phi^4$ inflation model can be significantly
    lowered, hence letting the ${1/4}\lambda \phi^4$ model, which is ruled out by
    the Wilkinson Microwave Anisotropy Probe (WMAP) data combined with SDSS data,
    get back into the observationally allowed region.

    DOI: 10.1088/0264-9381/24/6/015

    arXiv

    その他リンク: http://arxiv.org/pdf/astro-ph/0606228v2

  120. Wronskian Formulation of the Spectrum of Curvature Perturbations 査読有り

    Shuichiro Yokoyama, Takahiro Tanaka, Misao Sasaki, Ewan D. Stewart

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 6 )   2006年5月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    We present a new formulation for the evaluation of the primordial spectrum of
    curvature perturbations generated during inflation, using the fact that the
    Wronskian of the scalar field perturbation equation is constant. In the
    literature, there are many works on the same issue focusing on a few specific
    aspects or effects. Here we deal with the general multi-component scalar field,
    and show that our new formalism gives a method to evaluate the final amplitude
    of the curvature perturbation systematically and economically. The advantage of
    the new method is that one only has to solve a single mode of the scalar field
    perturbation equation backward in time from the end of inflation to the stage
    at which the perturbation is within the Hubble horizon, at which the initial
    values of the scalar field perturbations are given. We also clarify the
    relation of the new method with the new delta N formalism recently developed in
    Lee et al.(2005).

    DOI: 10.1088/1475-7516/2006/06/020

    Web of Science

    arXiv

    その他リンク: http://arxiv.org/pdf/astro-ph/0605021v2

  121. A New delta N Formalism for Multi-Component Inflation 査読有り

    Hyun-Chul Lee, Misao Sasaki, Ewan D. Stewart, Takahiro Tanaka, Shuichiro Yokoyama

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 10 )   2005年6月

     詳細を見る

    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    The delta N formula that relates the final curvature perturbation on comoving
    slices to the inflaton perturbation on flat slices after horizon crossing is a
    powerful and intuitive tool to compute the curvature perturbation spectrum from
    inflation. However, it is customarily assumed further that the conventional
    slow-roll condition is satisfied, and satisfied by all components, during
    horizon crossing. In this paper, we develop a new delta N formalism for
    multi-component inflation that can be applied in the most general situations.
    This allows us to generalize the idea of general slow-roll inflation to the
    multi-component case, in particular only applying the general slow-roll
    condition to the relevant component. We compute the power spectrum of the
    curvature perturbation in multi-component general slow-roll inflation, and find
    that under quite general conditions it is invertible.

    DOI: 10.1088/1475-7516/2005/10/004

    Web of Science

    arXiv

    その他リンク: http://arxiv.org/pdf/astro-ph/0506262v2

▼全件表示

MISC 1

  1. Japanese Cosmic Dawn/Epoch of Reionization Science with the Square Kilometre Array

    Kenji Hasegawa, Shinsuke Asaba, Kiyotomo Ichiki, Akio K. Inoue, Susumu Inoue, Tomoaki Ishiyama, Hayato Shimabukuro, Keitaro Takahashi, Hiroyuki Tashiro, Hidenobu Yajima, Shu-ichiro Yokoyama, Kohji Yoshikawa, Shintaro Yoshiura, on behalf of Japan, SKA consortium, EoR Science Working Group  

        2016年3月

     詳細を見る

    Cosmic reionization is known to be a major phase transition of the gas in the<br />
    Universe. Since astronomical objects formed in the early Universe, such as the<br />
    first stars, galaxies and black holes, are expected to have caused cosmic<br />
    reionization, the formation history and properties of such objects are closely<br />
    related to the reionization process. In spite of the importance of exploring<br />
    reionization, our understandings regarding reionization is not sufficient yet.<br />
    Square Kilometre Array (SKA) is a next-generation large telescope that will be<br />
    operated in the next decade. Although several programs of next-generation<br />
    telescopes are currently scheduled, the SKA will be the unique telescope with a<br />
    potential to directly observe neutral hydrogen up to z~30, and provide us with<br />
    valuable information on the Cosmic Dawn (CD) and the Epoch of Reionization<br />
    (EoR). The early science with the SKA will start in a few years; it is thus the<br />
    time for us to elaborate a strategy for CD/EoR Science with the SKA. The<br />
    purpose of this document is to introduce Japanese scientific interests in the<br />
    SKA project and to report results of our investigation.

    arXiv

講演・口頭発表等 6

  1. GWB anisotropies 招待有り 国際共著 国際会議

    Yokoyama Shuchiro

    2023 Winter-II NRF-JSPS Workshop in particle physics, cosmology, and gravitation  2023年2月7日  Jinn-Ouk Gong (Ewha, chair), Tomo Takahashi (Saga, chair)

     詳細を見る

    開催年月日: 2023年2月

    記述言語:英語   会議種別:口頭発表(招待・特別)  

    開催地:Seoul, Korea   国名:大韓民国  

  2. What do the CMB observations tell us about inflation? 招待有り 国際会議

    Yokoyama Shuichiro

    10th JSPS Core-to-Core program CMB Japan group seminar for young scientists  2022年12月27日  JSPS Core-to-Core program CMB Japan group

     詳細を見る

    開催年月日: 2022年12月

    記述言語:英語   会議種別:口頭発表(基調)  

    開催地:online  

  3. Multi-chaotic inflation with the curvaton and its application to the sneutrinos scenario

    2022年9月6日 

     詳細を見る

    開催年月日: 2022年9月

    記述言語:日本語   会議種別:口頭発表(一般)  

  4. Multi-chaotic inflation with and without spectator field 招待有り 国際会議

    Yokoyama Shuichiro

    2022 Summer NRF-JSPS Workshop in particle physics, cosmology, and gravitation  2022年7月7日  Jinn-Ouk Gong (Ewha, chair), Tomo Takahashi (Saga, chair), Masahide Yamaguchi (Tokyo Tech)

     詳細を見る

    開催年月日: 2022年7月

    記述言語:英語   会議種別:口頭発表(招待・特別)  

  5. 最近の原始ブラックホール研究に関して 招待有り

    横山修一郎

    初代星・初代銀河研究会2021  2022年2月17日 

     詳細を見る

    開催年月日: 2022年2月

    記述言語:日本語   会議種別:口頭発表(招待・特別)  

    開催地:online+東京  

  6. Violation of slow-roll in non-minimal inflation 国際共著 国際会議

    Shuichiro Yokoyama

    online JGRG 2020  2020年11月25日 

     詳細を見る

    開催年月日: 2020年11月

    記述言語:英語   会議種別:ポスター発表  

    国名:日本国  

▼全件表示

科研費 6

  1. すばる望遠鏡HSCの最終データを用いた宇宙の加速膨張の起源の解明

    研究課題/研究課題番号:20H01932  2020年4月 - 2024年3月

    科学研究費助成事業  基盤研究(B)

    宮武 広直, 西澤 淳, 横山 修一郎

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    担当区分:研究分担者 

    宇宙の加速膨張は現代物理学における最大の謎の一つである。加速膨張は未知の暗黒エネルギーによって引き起こされているとする一方で、アインシュタインの一般相対性理論の修正が必要だとする指摘もある。本研究では、すばる望遠鏡Hyper Suprime-Cam(HSC)による広視野深宇宙撮像銀河サーベイの最終年度のデータを用いて弱重力レンズ効果を測定することで、世界最高精度で宇宙の加速膨張の性質を測定し、暗黒エネルギーの性質及び修正重力理論の兆候に制限を課すことを目指す。そのために、機械学習を用いて観測的系統誤差を低減し、修正重力理論を考慮に入れた弱重力レンズ観測量のモデルを構築する。
    本年度はすばる望遠鏡HSCサーベイ初年度のデータとSDSS BOSSサーベイの分光銀河サンプルを組み合わせ、銀河弱重力レンズ信号と銀河クラスタリング信号を組み合わせることにより、宇宙構造の凸凹(S8)に制限を付けた。この際、昨年度までに構築した非線形領域まで適用できる観測量の精密モデルを用いることで、米国がリードするDark Energy Survey, 欧州がリードするKilo Degree Surveyと同等の制限を得ることができた。この結果は論文として投稿し、現在査読中である。
    また、HSCサーベイ3年目までのデータを用いた銀河形状カタログのシミュレーション画像を用いた系統誤差の評価が完了し、論文として発表した。来年度はこのデータを用いた同様の宇宙論解析を行う予定である。
    ブレンド画像同定のアルゴリズムの開発状況であるが、EL-COSMOSと呼ばれるCOSMOS領域の各銀河に対して予測されるスペクトルを付加したカタログを用いることにより、教師データのシミュレーション画像に色情報を追加することに成功した。今後はこの教師データを用いて機械学習を行い、ブレンド画像同定のアルゴリズムの開発を進める。
    また、HSC初年度のデータで得られた宇宙論的弱重力レンズ信号を用いて修正重力理論を制限する研究を進め、測定、モデルにおける系統誤差を注意深く調べながらmu-Sigmaと呼ばれる現象論的パラメータ空間での制限を得るに至った。この結果は修士論文としてまとめられ、来年度中に論文誌に投稿予定である。
    HSC初年度のデータを用いた解析が完了し、また3年目までの銀河形状カタログが完成し、そのデータを用いた宇宙論解析の準備も整ったため。さらに、ブレンド画像同定のためのシミュレーションツールのアップグレード、初年度のデータを用いた修正重力理論の検証も行うことができたため。
    来年度はHSC3年目までのデータを用いた宇宙論解析を行う。これにより約2倍測定制度が良くなると期待される。また、ブレンド画像同定のアルゴリズムの完成を目指すとともに、3年目までのデータを用いた修正重力理論の検証を行う。

  2. 精密宇宙論時代における初期揺らぎの統計的性質の徹底解明と超高エネルギー物理の検証

    研究課題/研究課題番号:20K03968  2020年4月 - 2023年3月

    日本学術振興会  科学研究費助成事業  基盤研究(C)

    横山 修一郎

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    担当区分:研究代表者 

    配分額:4290000円 ( 直接経費:3300000円 、 間接経費:990000円 )

    宇宙論的初期ゆらぎの統計的性質(非ガウス性、 統計的非等方性)に着目し、(A) 様々な初期宇宙モデルにおける宇宙論的揺らぎの生成、進 化の精査、(B)現在進行中、そして将来の宇宙論的観測を用いた検証についての考察を行う。 最終的には、より精密なボトムアップ的初期宇宙モデル構築を目指し、究極理論に迫る。
    2021年度は、本研究課題に関連する論文を学術誌に6本投稿、うち3本は受理され出版済み、3本は査読中である。また、国際学会で3件、国内学会でも1件の招待講演を行った。いずれもオンラインでの講演である。出版した論文では、まず「超高エネルギー物理の検証」という観点から、超高エネルギー状態を記述する理論が共形対称性を持っている場合に考えられるインフレーション模型に着目し、特に重力理論が計量アフィン幾何に基づく場合には理論が高階微分項を持っていたとしても共形対称性と無矛盾な模型を構成可能であることを示した。その上で、宇宙マイクロ波背景輻射観測との整合性を議論し、さらには将来の重力波干渉計による模型の検証可能性についても議論した。また、「精密宇宙論時代における初期揺らぎの統計的性質の解明」という点に関して、将来の大規模銀河サーベイを用いた、スケールに依存する非ガウス性への観測的制限の評価、原始ブラックホール形成における初期揺らぎの非ガウス性の影響の精査を行なった。
    研究費に関して、計上していた学会参加などにかかる旅費がコロナの影響により使用できなかったため、2022年度に繰り越す形をとった。
    研究実績の概要にも記したように、コロナ禍にも関わらず課題に沿った研究成果を残すことができた。2022年度は、コロナによる規制が緩和されることが期待され、これらの研究成果を海外、国内の研究会に参加し、発表していく予定である。
    2021年度の研究成果の一つである、原始ブラックホール形成過程における非ガウス性の影響に関連して、原始ブラックホール形成に付随して生成すると考えられる背景重力波への非ガウス性の影響の精査を行う。また、超高エネルギー物理の検証という課題に関しては、インフレーション模型への観測的制限をもとに多成分スカラー場インフレーション模型の精査を行い、具体的な素粒子模型との整合性に関する議論を行う。また、積極的に海外、国内研究会に参加し、研究成果の発表を行う。

  3. 原始ブラックホール形成過程の精査とその観測的検証

    研究課題/研究課題番号:18H04356  2018年4月 - 2020年3月

    日本学術振興会  科学研究費助成事業  新学術領域研究(研究領域提案型)

    横山 修一郎

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    担当区分:研究代表者 

    配分額:2600000円 ( 直接経費:2000000円 、 間接経費:600000円 )

    本研究は「原始ブラックホール」に焦点を当て、ボトムアップ的アプローチでインフレーション理論に迫ることを目的とする。平成31年(令和元年)度は、昨年度の研究実績報告書にも記載したが、査読段階であった「重力レンズ効果を用いた系外惑星探査データの原始ブラックホール量制限への応用」に関する論文をPhysical Review D誌で発表、またそれと関連するインフレーション模型に関する研究についてもPhysical Review D誌で発表した。
    さらに交付申請書の「平成31年度計画」に記載した「原始ブラックホールの空間分布」に関する研究を進め、原始ブラックホールの種となる初期密度揺らぎがガウス分布からずれることで原始ブラックホールがクラスタリングする可能性を示した論文を2編発表した。非ガウス性の影響は空間分布だけでなく、生成量にも影響を与えるが、その影響を精査した論文も1編発表した。また、原始ブラックホールの種となる初期密度揺らぎのパワースペクトルが広がりを持っている場合に有用な評価法を提唱、論文としてまとめた。以上形成過程のみならず、観測的検証の派生的研究として、原始ブラックホール存在量の観測的制限を用いて、原始磁場の存在に制限を与えた。論文としてまとめ、2020年4月現在査読中である。
    以上の研究成果は、論文としてのみならず、国内外の研究会でも発表、そのうち2件は招待講演である。
    令和元年度が最終年度であるため、記入しない。
    令和元年度が最終年度であるため、記入しない。

  4. 複数場インフレーションモデルの検証に関する理論的研究

    研究課題/研究課題番号:16H01103  2016年4月 - 2018年3月

    日本学術振興会  科学研究費助成事業  新学術領域研究(研究領域提案型)

    横山 修一郎

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    担当区分:研究代表者 

    配分額:2080000円 ( 直接経費:1600000円 、 間接経費:480000円 )

    平成29年度は、最終年度であり、これまでの研究成果を論文としてまとめることを中心に行った。まず、当初の研究計画にも記載した、複数場インフレーションモデルにおける物質等曲率ゆらぎの精密評価を行い、観測から示唆されるモデルへの制限が従来のものほど厳しくならないことを示した研究を論文として出版した。また、将来の21cm線観測による初期ゆらぎの小スケールゆらぎについての情報を用いた、複数場インフレーションモデルの峻別可能性に関する研究も論文として出版した。加えて、原始ブラックホールに関する研究論文も3本発表した。原始ブラックホールは、複数場インフレーションモデルの可能性を議論する上でも、有用な天体であると考えられている。特に、LIGOによる重力波検出を通じて、ブラックホール連星の存在が明らかとなり、その連星が原始ブラックホールである可能性に関する研究が世界中で行われている。そのような研究背景のもと、将来の重力波観測による原始ブラックホール検出の可能性に関する研究を行った。ブラックホールのスピン分布や、合体頻度の質量分布に原始ブラックホール特有の振る舞いがあることを示した。
    さらに、当該の新学術領域研究の計画研究班A01, A03, B01合同研究会を主催した。核計画研究班のメンバーを中心として、30名程度の比較的小さな研究会であったが、活発な議論が行われ、班をまたいだ新たな研究計画も生まれるなど非常に有意義な会議となった。
    29年度が最終年度であるため、記入しない。
    29年度が最終年度であるため、記入しない。

  5. 宇宙論的観測で探る初期揺らぎの非線形性と初期宇宙モデルの検証

    研究課題/研究課題番号:15K17659  2015年4月 - 2019年3月

    日本学術振興会  科学研究費助成事業 若手研究(B)  若手研究(B)

    横山 修一郎

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    担当区分:研究代表者 

    配分額:3250000円 ( 直接経費:2500000円 、 間接経費:750000円 )

    将来計画されている精密かつ大規模な宇宙論的観測による、インフレーションをはじめとした初期宇宙モデルの検証可能性についての研究を行った。結果として、これまで峻別が難しかったインフレーションモデルに対しても新たな知見が得られる可能性がわかった。
    また、大きな成果として、2015年に初検出された連星ブラックホールからの重力波の源が原始ブラックホールである可能性を指摘し、原始ブラックホール研究、さらには初期宇宙研究の新たな方向性を示した。
    上記本研究で得られた結果により、2020年代の精密宇宙論的観測を通じて超高温高密度状態であったと考えられる初期宇宙の様子がより明らかになっていくことが期待される。つまり、地上実験では到底到達不可能なエネルギー状態における物理学の検証につながると考えられる。現在の物理学の基礎となっている素粒子標準模型や一般相対性理論がそのような高エネルギー状態で適用可能かどうかについての重要な知見が得られると考えられ、真の物理理論は何かという問いに迫るという意味で学術的に重要である。

  6. 宇宙論的観測で探る初期揺らぎの非ガウス性と初期宇宙モデルの検証

    研究課題/研究課題番号:12J02775  2012年4月 - 2015年3月

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    横山 修一郎

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    本研究では、進展著しい宇宙論的観測を用いて初期密度揺らぎの非ガウス性を探り、初期宇宙モデルを検証する。研究の方向として大きく二つ挙げられる。1.個々のインフレーションモデルに対する初期密度揺らぎの非ガウス性を中心とした理論予言の精密な評価、2.様々な宇宙論的スケールでの揺らぎの観測に対する非ガウス性の影響の評価である。
    平成26年度は、BICEP2による「背景重力波」についての報告や、Planck衛星の結果報告といった詳細な宇宙論的観測結果が発表された年であった。そのような背景のもと、研究テーマのキーワードの一つでもある初期密度揺らぎの非ガウス性と背景重力波に関する研究を遂行した。大きな初期ゆらぎの非ガウス性を予言するモデルとして、カーバトンモデルと呼ばれるものがある。本年度はそのモデルに着目し、背景重力波観測から得られるカーバトンモデルに対する予言についての研究や、より詳細なモデルについての解析を行なった。
    さらに新たな背景重力波生成シナリオの可能性についての議論についても行なった。これらは上で述べた研究の方向性の1に関連する。2に関連する仕事として、宇宙マイクロ波背景輻射のプランク分布からのずれに対する初期揺らぎの非ガウス性が与える影響を調べた。さらに、将来の大型電波干渉計を用いると、初期揺らぎの非ガウス性をより精密に測定することができると期待されているが、その観測量に対する精密な理論予言を行なった。とくに、非ガウス性を測定するための観測量における天体起源の影響について精査した。

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