Updated on 2021/10/25

写真a

 
TADA Yuichiro
 
Organization
Institute for Advanced Research Designated assistant professor
Graduate School of Science Designated assistant professor
Title
Designated assistant professor
Contact information
メールアドレス
External link

Degree 1

  1. 博士(理学) ( 2017.3   東京大学 ) 

Research Interests 4

  1. Early Universe

  2. Inflation

  3. Primordial Black Hole

  4. Gravitational wave

Research Areas 1

  1. Natural Science / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics

Research History 6

  1. Nagoya University   Institute for Advanced Research   Designated assistant professor

    2021.4

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    Country:Japan

  2. Daido University   Lecturer (part-time)

    2019.4 - 2021.3

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    Country:Japan

    Notes:Classical mechanics 1, 2

  3. Nagoya University   Cosmology group   JSPS Fellow PD

    2018.4 - 2021.3

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    Country:Japan

  4. Institute d'Astrophysique de Paris   Dr. Sébastien Renaux-Petel's Group   PD researcher

    2017.4 - 2018.3

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    Country:France

  5. The University of Tokyo   Kavli IPMU, ICRR   JSPS Fellow DC2

    2015.4 - 2017.3

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    Country:Japan

  6. The University of Tokyo   Kavli IPMU, ICRR   ALPS Fellow

    2012.10 - 2017.3

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    Country:Japan

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Education 3

  1. The University of Tokyo   Graduate School of Science

    2014.4 - 2017.3

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    Country: Japan

    Notes: Ph.D.

  2. The University of Tokyo   Graduate School of Science

    2012.4 - 2014.3

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    Country: Japan

    Notes: M.Sc. in Physics

  3. The University of Tokyo   Faculty of Science   Department of Physics

    2008.4 - 2012.3

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    Country: Japan

Professional Memberships 1

  1. The Physical Society of Japan

    2013.6

Awards 1

  1. Outstanding Presentation Award Gold Prize

    2020.11   Online JGRG workshop 2020   Manifestly covariant theory of stochastic inflation

 

Papers 24

  1. Primordial black holes in peak theory with a non-Gaussian tail Reviewed

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

    Journal of Cosmology and Astroparticle Physics   Vol. 2021 ( 10 ) page: 053 - 053   2021.10

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    Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

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

    Other Link: https://iopscience.iop.org/article/10.1088/1475-7516/2021/10/053/pdf

  2. Revisiting non-Gaussianity in non-attractor inflation models in the light of the cosmological soft theorem Reviewed

    Suyama T., Tada Y., Yamaguchi M.

    Progress of Theoretical and Experimental Physics   Vol. 2021 ( 7 )   2021.7

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    Language:Japanese   Publisher:Progress of Theoretical and Experimental Physics  

    We revisit squeezed-limit non-Gaussianity in single-field non-attractor inflation models from the viewpoint of the cosmological soft theorem. In single-field attractor models, an inflaton's trajectories with different initial conditions effectively converge into a single trajectory in the phase space, and hence there is only one clock degree of freedom (DoF) in the scalar part. Its long-wavelength perturbations can be absorbed into the local coordinate renormalization and lead to the so-called consistency relation between n- and (n+1)-point functions. On the other hand, if the inflaton dynamics deviates from the attractor behavior, its long-wavelength perturbations cannot necessarily be absorbed and the consistency relation is expected not to hold any longer. In this work, we derive a formula for the squeezed bispectrum including the explicit correction to the consistency relation, as a proof of its violation in the non-attractor cases. First one must recall that non-attractor inflation needs to be followed by attractor inflation in a realistic case. Then, even if a specific non-attractor phase is effectively governed by a single DoF of phase space (represented by the exact ultra-slow-roll limit) and followed by a single-DoF attractor phase, its transition phase necessarily involves two DoF in dynamics and hence its long-wavelength perturbations cannot be absorbed into the local coordinate renormalization. Thus, it can affect local physics, even taking account of the so-called local observer effect, as shown by the fact that the bispectrum in the squeezed limit can go beyond the consistency relation. More concretely, the observed squeezed bispectrum does not vanish in general for long-wavelength perturbations exiting the horizon during a non-attractor phase.

    DOI: 10.1093/ptep/ptab063

    Scopus

  3. Induced gravitational waves as a cosmological probe of the sound speed during the QCD phase transition Reviewed

    Katsuya T. Abe, Yuichiro Tada, Ikumi Ueda

    Journal of Cosmology and Astroparticle Physics   Vol. 2021 ( 06 ) page: 048 - 048   2021.6

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

    DOI: 10.1088/1475-7516/2021/06/048

    Scopus

    arXiv

    Other Link: https://iopscience.iop.org/article/10.1088/1475-7516/2021/06/048/pdf

  4. Minimal k -inflation in light of the conformal metric-affine geometry Reviewed

    Mikura Y., Tada Y., Yokoyama S.

    Physical Review D   Vol. 103 ( 10 )   2021.5

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    Language:Japanese   Publisher:Physical Review D  

    We motivate a minimal realization of slow-roll k-inflation by incorporating the local conformal symmetry and the broken global SO(1,1) symmetry in the metric-affine geometry. With use of the metric-affine geometry where both the metric and the affine connection are treated as independent variables, the local conformal symmetry can be preserved in each term of the Lagrangian and thus higher derivatives of scalar fields can be easily added in a conformally invariant way. Predictions of this minimal slow-roll k-inflation, ns∼0.96, r∼0.005, and cs∼0.03, are not only consistent with current observational data but also have a prospect to be tested by forthcoming observations.

    DOI: 10.1103/PhysRevD.103.L101303

    Scopus

  5. A manifestly covariant theory of multifield stochastic inflation in phase space: solving the discretisation ambiguity in stochastic inflation Reviewed

    Lucas Pinol, Sébastien Renaux-Petel, Yuichiro Tada

    Journal of Cosmology and Astroparticle Physics   Vol. 2021 ( 04 ) page: 048 - 048   2021.4

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

    DOI: 10.1088/1475-7516/2021/04/048

    Scopus

    arXiv

    Other Link: https://iopscience.iop.org/article/10.1088/1475-7516/2021/04/048/pdf

  6. Conformal inflation in the metric-affine geometry Reviewed

    Y. Mikura, Y. Tada, S. Yokoyama

    EPL (Europhysics Letters)   Vol. 132 ( 3 ) page: 39001 - 39001   2020.11

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

    DOI: 10.1209/0295-5075/132/39001

    Web of Science

    Scopus

    Other Link: https://iopscience.iop.org/article/10.1209/0295-5075/132/39001/pdf

  7. Local observer effect on the cosmological soft theorem Reviewed

    Teruaki Suyama, Yuichiro Tada, Masahide Yamaguchi

    Progress of Theoretical and Experimental Physics   Vol. 2020 ( 11 )   2020.11

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Oxford University Press (OUP)  

    <title>Abstract</title>
    Non-Gaussianities of primordial perturbations in the soft limit provide important information about the light degrees of freedom during inflation. The soft modes of the curvature perturbations, unobservable for a local observer, act to rescale the spatial coordinates. We determine how the trispectrum in the collapsed limit is shifted by the rescaling due to the soft modes. We find that the form of the inequality between the $f_\mathrm{NL}$ and $\tau_\mathrm{NL}$ parameters is not affected by the rescaling, demonstrating that the role of the inequality as an indicator of the light degrees of freedom remains intact. We also comment on the local observer effect on the consistency relation for ultra-slow-roll inflation.

    DOI: 10.1093/ptep/ptaa144

    Web of Science

    Scopus

    Other Link: http://academic.oup.com/ptep/article-pdf/2020/11/113E01/34299933/ptaa144.pdf

  8. Escape from the swampland with a spectator field Reviewed

    Kazuhiro Kogai, Yuichiro Tada

    Physical Review D   Vol. 101 ( 10 )   2020.5

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.101.103514

    Web of Science

    Scopus

  9. Stochastic inflation with an extremely large number of e-folds Reviewed

    Naoya Kitajima, Yuichiro Tada, Fuminobu Takahashi

    Physics Letters B   Vol. 800   2020.1

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.physletb.2019.135097

    Web of Science

    Scopus

  10. Primordial black hole tower: Dark matter, earth-mass, and LIGO black holes Reviewed

    Yuichiro Tada, Shuichiro Yokoyama

    Physical Review D   Vol. 100 ( 2 )   2019.7

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:American Physical Society ({APS})  

    DOI: 10.1103/PhysRevD.100.023537

    Web of Science

  11. Inflationary stochastic anomalies Reviewed

    Lucas Pinol, Sébastien Renaux-Petel, Yuichiro Tada

    Class. Quant. Grav.   Vol. 36 ( 7 )   2019.4

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    The stochastic approach aims at describing the long-wavelength part of quantum fields during inflation by a classical stochastic theory. It is usually formulated in terms of Langevin equations, giving rise to a Fokker-Planck equation for the probability distribution function of the fields, and possibly their momenta. The link between these two descriptions is ambiguous in general, as it depends on an implicit discretisation procedure, the two prominent ones being the It\^o and Stratonovich prescriptions. Here we show that the requirement of general covariance under field redefinitions is verified only in the latter case, however at the expense of introducing spurious `frame' dependences. This stochastic anomaly disappears when there is only one source of stochasticity, like in slow-roll single-field inflation, but manifests itself when taking into account the full phase space, or in the presence of multiple fields. Despite these difficulties, we use physical arguments to write down a covariant Fokker-Planck equation that describes the diffusion of light scalar fields in non-linear sigma models in the overdamped limit. We apply it to test scalar fields in de Sitter space and show that some statistical properties of a class of two-field models with derivative interactions can be reproduced by using a correspondence with a single-field model endowed with an effective potential. We also present explicit results in a simple extension of the single-field $\lambda \phi^4$ theory to a hyperbolic field space geometry. The difficulties we describe seem to be the stochastic counterparts of the notoriously difficult problem of maintaining general covariance in quantum theories, and the related choices of operator ordering and path-integral constructions. Our work thus opens new avenues of research at the crossroad between cosmology, statistical physics, and quantum field theory.

    DOI: 10.1088/1361-6382/ab097f

    Web of Science

    Scopus

  12. Does the detection of primordial gravitational waves exclude low energy inflation? Reviewed

    Tomohiro Fujita, Ryo Namba, Yuichiro Tada

    Physics Letters B   Vol. 778   page: 17 - 21   2018.3

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Elsevier {BV}  

    DOI: 10.1016/j.physletb.2017.12.014

    Web of Science

  13. $\mathcal O(10) M_⊙$ primordial black holes and string axion dark matter Reviewed

    Inomata, Keisuke, Kawasaki, Masahiro, Mukaida, Kyohei, Tada, Yuichiro, Yanagida, Tsutomu T.

    Phys. Rev.   Vol. 96 ( 12 ) page: 123527 - 123527   2017.12

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.96.123527

    Web of Science

  14. Inflationary Primordial Black Holes as All Dark Matter Reviewed

    Inomata, Keisuke, Kawasaki, Masahiro, Mukaida, Kyohei, Tada, Yuichiro, Yanagida, Tsutomu T.

    Phys. Rev.   Vol. 96 ( 4 ) page: 043504 - 043504   2017.8

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.96.043504

    Web of Science

  15. Inflationary primordial black holes for the LIGO gravitational wave events and pulsar timing array experiments Reviewed

    Inomata, Keisuke, Kawasaki, Masahiro, Mukaida, Kyohei, Tada, Yuichiro, Yanagida, Tsutomu T.

    Phys. Rev.   Vol. 95 ( 12 ) page: 123510 - 123510   2017.6

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.95.123510

    Web of Science

  16. Squeezed bispectrum in the $δ N$ formalism: local observer effect in field space Reviewed

    Tada, Yuichiro, Vennin, Vincent

    JCAP   Vol. 1702 ( 2 ) page: 021 - 021   2017.2

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1088/1475-7516/2017/02/021

    Web of Science

  17. Primordial black holes as dark matter in supergravity inflation models Reviewed

    Kawasaki, Masahiro, Kusenko, Alex, er, Tada, Yuichiro, Yanagida, Tsutomu T.

    Phys. Rev.   Vol. 94 ( 8 ) page: 083523 - 083523   2016.10

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.94.083523

    Web of Science

  18. Revisiting constraints on small scale perturbations from big-bang nucleosynthesis Reviewed

    Inomata, Keisuke, Kawasaki, Masahiro, Tada, Yuichiro

    Phys. Rev.   Vol. 94 ( 4 ) page: 043527 - 043527   2016.8

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.94.043527

    Web of Science

  19. Can massive primordial black holes be produced in mild waterfall hybrid inflation? Reviewed

    Kawasaki, Masahiro, Tada, Yuichiro

    JCAP   Vol. 1608 ( 8 ) page: 041 - 041   2016.8

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1088/1475-7516/2016/08/041

    Web of Science

  20. Primordial black holes as biased tracers Reviewed

    Tada, Yuichiro, Yokoyama, Shuichiro

    Phys. Rev.   Vol. 91 ( 12 ) page: 123534 - 123534   2015.6

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.91.123534

    Web of Science

  21. Consistent generation of magnetic fields in axion inflation models Reviewed

    Fujita, Tomohiro, Namba, Ryo, Tada, Yuichiro, Takeda, Naoyuki, Tashiro, Hiroyuki

    JCAP   Vol. 1505 ( 5 ) page: 054 - 054   2015.5

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1088/1475-7516/2015/05/054

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    Scopus

  22. Anisotropic CMB distortions from non-Gaussian isocurvature perturbations Reviewed

    Ota, Atsuhisa, Sekiguchi, Toyokazu, Tada, Yuichiro, Yokoyama, Shuichiro

    JCAP   Vol. 1503 ( 3 ) page: 013 - 013   2015.3

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

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

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  23. Non-perturbative approach for curvature perturbations in stochastic $δ N$ formalism Reviewed

    Fujita, Tomohiro, Kawasaki, Masahiro, Tada, Yuichiro

    JCAP   Vol. 1410 ( 10 ) page: 030 - 030   2014.10

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1088/1475-7516/2014/10/030

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  24. A new algorithm for calculating the curvature perturbations in stochastic inflation Reviewed

    Fujita, Tomohiro, Kawasaki, Masahiro, Tada, Yuichiro, Takesako, Tomohiro

    JCAP   Vol. 1312 ( 12 ) page: 036 - 036   2013.12

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1088/1475-7516/2013/12/036

    Web of Science

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MISC 1

  1. On UV-completion of Palatini-Higgs inflation

    Yusuke Mikura, Yuichiro Tada

        2021.10

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    We investigate the UV-completion of the Higgs inflation in the metric and the
    Palatini formalisms. It is known that the cutoff scales for the perturbative
    unitarity of these inflation models become much smaller than the Planck scale
    to be consistent with observations. Expecting that the low cutoff scale
    originates in the curvature of a field-space spanned by the Higgs fields, we
    consider embedding the curved field-space into a higher dimensional flat space
    and apply this procedure to the metric-Higgs and the Palatini-Higgs scenarios.
    The new field introduced in this way successfully flattens the field-space and
    UV-completes the Higgs inflation in the metric formalism. However, in the
    Palatini formalism, the new field cannot uplift the cutoff up to the Planck
    scale. We also discuss the unavoidable low cutoff in the Palatini formalism in
    the context of the local conformal symmetry.

    arXiv

    Other Link: http://arxiv.org/pdf/2110.03925v1

Presentations 2

  1. 宇宙の「インフレ」と「金融工学」 Invited

    多田祐一郎

    名大発アカデミックフラッシュ 第2報  2021.9.3 

  2. 星が先かブラックホールが先か?原始ブラックホール研究の最前線 Invited

    多田祐一郎

    名古屋大学・名古屋市科学館 公開オンラインセミナー  2021.8.22 

KAKENHI (Grants-in-Aid for Scientific Research) 4

  1. Inflationary universe in light of stochastic calculus, primordial black holes, and gravitational waves

    Grant number:21K13918  2021.4 - 2024.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Early-Career Scientists

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    Authorship:Principal investigator 

    Grant amount:\4680000 ( Direct Cost: \3600000 、 Indirect Cost:\1080000 )

  2. Aspects of gravity and quantum theory in the stochastic formalism

    Grant number:19K14707  2019.4 - 2021.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Early-Career Scientists  Grant-in-Aid for Early-Career Scientists

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    Authorship:Principal investigator 

    Grant amount:\1560000 ( Direct Cost: \1200000 、 Indirect Cost:\360000 )

  3. Curvature Perturbations and Primordial Black Hole Formation in the Inflationary Universe

    Grant number:18J01992  2018.4 - 2021.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for JSPS Fellows  Grant-in-Aid for JSPS Fellows

  4. 小スケール曲率ゆらぎの観測とインフレーション

    Grant number:15J10829  2015.4 - 2017.3

    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

    多田 祐一郎

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    昨年度は5本の論文 (arXiv:1605.04646, 1606.07631, 1609.08876, 1611.06130, 1701.02544) を提出した。1つ目の論文では小スケールにもし大きな曲率ゆらぎが生じていた場合、それがビッグバン元素合成に与える影響について再考察し、既存の結果が定性的レベルで修正されることを示した。また3つ目の論文では、曲率ゆらぎのスクィーズド極限バイスペクトルに関し、近年指摘されているゲージ依存効果についての新たな理解を示し、簡単な計算アルゴリズムを提唱した。これは今後、実際に何らかの観測 (宇宙背景放射や銀河バイアス等) によってバイスペクトルを測定し、それを宇宙初期の物理と対応させるときに非常に重要になってくる。残りの論文では原始ブラックホールについて議論している。昨年 LIGO グループが初の重力波直接検出を発表し話題になったが、この重力波は重いブラックホール連星の合体から来ており、こうしたブラックホールが原始ブラックホールである可能性も注目されてきている。また伴って、原始ブラックホールが暗黒物質である可能性も再注目されてきた。そこで我々は実際に具体的なインフレーション模型を構築し、原始ブラックホールが LIGO の重力波イベントや暗黒物質を説明しうるか、また他に検出方法があるかどうかなどを検証した。
    これら研究成果に関し、国際会議で2度, 国内会議で1度口頭発表を行った. また国内外合わせて4つの研究機関でセミナー発表を行った.

 

Teaching Experience (Off-campus) 1

  1. Classical mechanics 1, 2

    2019.4 Daido University)