Exploring cosmology and astrophysics based on general scalar-tensor theories

• Project/Area Number: 16K17707
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Particle/Nuclear/Cosmic ray/Astro physics
• Research Institution: Rikkyo University
• Principal Investigator: KOBAYASHI Tsutomu 立教大学, 理学部, 教授 (40580212)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Project Status: Completed (Fiscal Year 2019)
• Budget Amount: ¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000); Fiscal Year 2019: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000); Fiscal Year 2018: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000); Fiscal Year 2017: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000); Fiscal Year 2016: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000)
• Keywords: インフレーション / 修正重力理論 / 宇宙論 / 中性子星 / 重力波 / 初期特異点

Outline of Final Research Achievements

I have explored various aspects of cosmology and astrophysics based on general scalar-tensor theories called the Horndeski and beyond-Horndeski theories. Focusing in particular on modified gravity theories consistent with the latest gravitational-wave observations, I have studied the screening mechanism, the evolution of density perturbations, and the structure of relativistic stars in order to place new constraints on such theories.

Academic Significance and Societal Importance of the Research Achievements

修正重力理論に対する理解が進んだことで、「重力を記述する基礎理論として、一般相対論はどの程度正しいのか？」という問いに対し、これまでよりも精度の高い回答を与えることができるようになった。特に、最新の重力波観測と関連させて重力理論の検証を狙ったところに科学的意義がある。
理論物理学の研究は自然科学のきわめて基礎的な側面に関わるものであり、ただちに社会的意義に直結するようなものではない。

Research Products

• [Int'l Joint Research] ポーツマス大学(英国)
• [Journal Article] Primordial non-Gaussianities of scalar and tensor perturbations in general bounce cosmology: Evading the no-go theorem (2020)
  • Author(s): Shingo Akama, Shin'chi Hirano, and Tsutomu Kobayashi
  • Journal Title: Physical Review D Volume: 101 Issue: 4 Pages: 43529-43529
  • DOI: 10.1103/physrevd.101.043529
  • Peer Reviewed / Open Access
• [Journal Article] Revisiting slow-roll dynamics and the tensor tilt in general single-field inflation (2020)
  • Author(s): Yosuke Mishima and Tsutomu Kobayashi
  • Journal Title: Physical Review D Volume: 101 Issue: 4 Pages: 43536-43536
  • DOI: 10.1103/physrevd.101.043536
  • Peer Reviewed
• [Journal Article] Relativistic stars in a cubic Galileon universe (2020)
  • Author(s): Hiromu Ogawa, Tsutomu Kobayashi, and Kazuya Koyama
  • Journal Title: Physical Review D Volume: 101 Issue: 2 Pages: 24026-24026
  • DOI: 10.1103/physrevd.101.024026
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Generalized 2D dilaton gravity and kinetic gravity braiding (2019)
  • Author(s): Kazufumi Takahashi and Tsutomu Kobayashi
  • Journal Title: Classical and Quantum Gravity Volume: 36 Issue: 9 Pages: 095003-095003
  • DOI: 10.1088/1361-6382/ab1355
  • Peer Reviewed
• [Journal Article] Horndeski theory and beyond: a review (2019)
  • Author(s): Tsutomu Kobayashi
  • Journal Title: Reports on Progress in Physics Volume: 82 Issue: 8 Pages: 1-27
  • DOI: 10.1088/1361-6633/ab2429
  • Peer Reviewed
• [Journal Article] Constraining degenerate higher-order scalar-tensor theories with linear growth of matter density fluctuations (2019)
  • Author(s): Shin'ichiro Hirano, Tsutomu Kobayashi, Daisuke Yamauchi, Shuichiro Yokoyama
  • Journal Title: Physical Review D Volume: 99 Issue: 10 Pages: 104051-104051
  • DOI: 10.1103/physrevd.99.104051
  • Peer Reviewed
• [Journal Article] Screening mechanism in degenerate higher-order scalar-tensor theories evading gravitational wave constraints (2019)
  • Author(s): Sinh'ichi Hirano, Tsutomu Kobayashi, Daisuke Yamauchi
  • Journal Title: Physical Review D Volume: 99 Issue: 10 Pages: 104073-104073
  • DOI: 10.1103/physrevd.99.104073
  • Peer Reviewed
• [Journal Article] Anti-screening of the Galileon force around a disk center hole (2019)
  • Author(s): Ogawa Hiromu、Hiramatsu Takashi、Kobayashi Tsutomu
  • Journal Title: Modern Physics Letters A Volume: 34 Issue: 02 Pages: 1950013-1950013
  • DOI: 10.1142/s0217732319500135
  • Peer Reviewed
• [Journal Article] General theory of cosmological perturbations in open and closed universes from the Horndeski action (2019)
  • Author(s): Akama Shingo、Kobayashi Tsutomu
  • Journal Title: Physical Review D Volume: 99 Issue: 4 Pages: 1-13
  • DOI: 10.1103/physrevd.99.043522
  • Peer Reviewed / Open Access
• [Journal Article] Matter bispectrum beyond Horndeski theories (2018)
  • Author(s): Hirano Shin’ichi、Kobayashi Tsutomu、Tashiro Hiroyuki、Yokoyama Shuichiro
  • Journal Title: Physical Review D Volume: 97 Issue: 10 Pages: 1-12
  • DOI: 10.1103/physrevd.97.103517
  • Peer Reviewed
• [Journal Article] Relativistic stars in degenerate higher-order scalar-tensor theories after GW170817 (2018)
  • Author(s): Kobayashi Tsutomu、Hiramatsu Takashi
  • Journal Title: Physical Review D Volume: 97 Issue: 10 Pages: 1-11
  • DOI: 10.1103/physrevd.97.104012
  • Peer Reviewed
• [Journal Article] Self-anisotropizing inflationary universe in Horndeski theory and beyond (2018)
  • Author(s): Tahara Hiroaki W. H.、Nishi Sakine、Kobayashi Tsutomu、Yokoyama Jun'ichi
  • Journal Title: Journal of Cosmology and Astroparticle Physics Volume: 2018 Issue: 07 Pages: 1-13
  • DOI: 10.1088/1475-7516/2018/07/058
  • Peer Reviewed
• [Journal Article] Parity-violating gravity and GW170817 (2018)
  • Author(s): Nishizawa Atsushi、Kobayashi Tsutomu
  • Journal Title: Physical Review D Volume: 98 Issue: 12 Pages: 1-5
  • DOI: 10.1103/physrevd.98.124018
  • NAID: 120006623784
  • Peer Reviewed
• [Journal Article] Extended cuscuton: formulation (2018)
  • Author(s): Iyonaga Aya、Takahashi Kazufumi、Kobayashi Tsutomu
  • Journal Title: Journal of Cosmology and Astroparticle Physics Volume: 2018 Issue: 12 Pages: 1-23
  • DOI: 10.1088/1475-7516/2018/12/002
  • Peer Reviewed
• [Journal Article] Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations (2017)
  • Author(s): Hirano Shin'ichi、Nishi Sakine、Kobayashi Tsutomu
  • Journal Title: JCAP Volume: 2017 Issue: 07 Pages: 009-009
  • DOI: 10.1088/1475-7516/2017/07/009
  • Peer Reviewed / Open Access
• [Journal Article] Extended mimetic gravity: Hamiltonian analysis and gradient instabilities (2017)
  • Author(s): Takahashi Kazufumi、Kobayashi Tsutomu
  • Journal Title: Phys. Rev. D Volume: 2017 Issue: 11 Pages: 038-038
  • DOI: 10.1088/1475-7516/2017/11/038
  • Peer Reviewed
• [Journal Article] Scale-invariant perturbations from NEC violation: A new variant of Galilean Genesis (2017)
  • Author(s): Sakine Nishi, Tsutomu Kobayashi
  • Journal Title: Physical Review Volume: D95 Issue: 6 Pages: 1-11
  • DOI: 10.1103/physrevd.95.064001
  • Peer Reviewed / Open Access / Acknowledgement Compliant
• [Journal Article] Generalized multi-Galileons, covariantized new terms, and the no-go theorem for non-singular cosmologies (2017)
  • Author(s): Shingo Akama, Tsutomu Kobayashi
  • Journal Title: Physical Review Volume: D95 Issue: 6 Pages: 1-7
  • DOI: 10.1103/physrevd.95.064011
  • Peer Reviewed / Acknowledgement Compliant
• [Journal Article] General invertible transformation and physical degrees of freedom (2017)
  • Author(s): Kazufumi Takahashi, Hayato Motohashi, Teruaki Suyama, Tsutomu Kobayashi
  • Journal Title: Physical Review Volume: 印刷中
  • Peer Reviewed / Acknowledgement Compliant
• [Journal Article] Ultra slow-roll G-inflation (2016)
  • Author(s): Shin'ichi Hirano, Tsutomu Kobayashi, Shuichiro Yokoyama
  • Journal Title: Physical Review Volume: D94 Issue: 10 Pages: 1-9
  • DOI: 10.1103/physrevd.94.103515
  • Peer Reviewed
• [Journal Article] Generic instabilities of nonsingular cosmologies in Horndeski theory: A no-go theorem (2016)
  • Author(s): Tsutomu Kobayashi
  • Journal Title: Physical Review Volume: D94 Issue: 4 Pages: 1-6
  • DOI: 10.1103/physrevd.94.043511
  • Peer Reviewed / Acknowledgement Compliant
• [Presentation] Revisiting slow-roll dynamics and the tensor tilt in general single-field inflation (2020)
  • Author(s): Tsutomu Kobayashi
  • Organizer: Cosmic Acceleration
  • Int'l Joint Research
• [Presentation] On the screening mechanism in DHOST theories evading gravitational wave constraints (2019)
  • Author(s): Tsutomu Kobayashi
  • Organizer: 日本物理学会秋季大会
• [Presentation] On the screening mechanism in DHOST theories evading gravitational wave constraints (2019)
  • Author(s): Tsutomu Kobayashi
  • Organizer: COSMO 19
  • Int'l Joint Research
• [Presentation] Vainshtein mechanism and its breaking in scalar-tensor theories (2019)
  • Author(s): Tsutomu Kobayashi
  • Organizer: 6th Korea-Japan workshop on dark energy
  • Int'l Joint Research / Invited
• [Presentation] One-loop matter power spectrum beyond Horndeski (2019)
  • Author(s): 小林努
  • Organizer: 日本物理学会年次大会
• [Presentation] Extended Cuscuton (2019)
  • Author(s): Tsutomu Kobayashi
  • Organizer: Why does the Universe accelerate? -Exhaustive study and challenge of the future
  • Int'l Joint Research
• [Presentation] Relativistic stars in degenerate higher-order scalar-tensor theories after GW170817 (2018)
  • Author(s): 小林努
  • Organizer: 日本物理学会秋季大会
• [Presentation] Parity-violating gravity and GW170817 (2018)
  • Author(s): 小林努
  • Organizer: 第 7 回観測的宇宙論ワークショップ
• [Presentation] 一般相対論とその拡張 (2018)
  • Author(s): 小林努
  • Organizer: 第 31 回理論懇シンポジウム
  • Invited
• [Presentation] Scalar-tensor theories after GW170817 and relativistic stars in DHOST (2018)
  • Author(s): Tsutomu Kobayashi
  • Organizer: MG15
  • Int'l Joint Research
• [Presentation] Scalar-tensor theories after GW170817 and relativistic stars in DHOST (2018)
  • Author(s): Tsutomu Kobayashi
  • Organizer: MOGRA2018
  • Int'l Joint Research
• [Presentation] Relativistic stars in degenerate higher-order scalar-tensor theories after GW170817 (2018)
  • Author(s): Tsutomu Kobayashi
  • Organizer: Essential next steps for gravity and cosmology
  • Int'l Joint Research
• [Presentation] Extended mimetic gravity: Hamiltonian analysis and gradient instabilities" (2018)
  • Author(s): Tsutomu Kobayashi
  • Organizer: The first annual symposium of the innovative area "Gravitational Wave Physics and Astronomy: Genesis"
  • Int'l Joint Research
• [Presentation] Generic instabilities of non-singular cosmologies in Horndeski theory: a no-go theorem (2017)
  • Author(s): Tsutomu Kobayashi
  • Organizer: COSMO17
  • Int'l Joint Research
• [Presentation] Generic instabilities of non-singular cosmologies in second-order theories: A no-go theorem (2017)
  • Author(s): Tsutomu Kobayashi
  • Organizer: 新学術領域「なぜ宇宙は加速するのか?- 徹底的究明と将来への挑戦 -」
  • Place of Presentation: KEK(茨城県つくば市)
  • Int'l Joint Research
• [Presentation] Primordial non-Gaussianities of gravitational waves beyond Horndeski (2016)
  • Author(s): Tsutomu Kobayashi
  • Organizer: 21st International Conference on General Relativity and Gravitation
  • Place of Presentation: Columbia University(ニューヨーク(アメリカ合衆国))
  • Int'l Joint Research
• [Presentation] Generic instabilities of non-singular cosmologies in Horndeski theory: a no-go theorem (2016)
  • Author(s): Tsutomu Kobayashi
  • Organizer: JGRG26
  • Place of Presentation: Osaka City University(大阪府大阪市)
  • Int'l Joint Research