| Project/Area Number |
20K14461
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| Research Category |
Grant-in-Aid for Early-Career Scientists
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| Allocation Type | Multi-year Fund |
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| Review Section |
Basic Section 15010:Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics
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| Research Institution | The University of Tokyo |
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Principal Investigator |
Pi Shi 東京大学, カブリ数物連携宇宙研究機構, 客員科学研究員 (60817518)
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| Project Period (FY) |
2020-04-01 – 2024-03-31
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| Project Status |
Completed (Fiscal Year 2023)
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| Budget Amount *help |
¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000)
Fiscal Year 2023: ¥260,000 (Direct Cost: ¥200,000、Indirect Cost: ¥60,000)
Fiscal Year 2022: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000)
Fiscal Year 2021: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2020: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000)
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| Keywords | 初期宇宙論 / 確率的重力波 / インフレーション / 原始ブラックホール / 宇宙論的摂動理論 / スカラー誘導重力波 / 非ガウス曲率摂動 / gravitational waves / primordial black holes / curvature perturbation / inflation / ultra slow roll / δN formalism / pulsar timing array / LISA / pulsa timing array / curvaton scenario / swampland conjecture / cosmology |
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| Outline of Research at the Start |
The discovery of gravitational wave in 2015 marks the dawn of gravitational wave astronomy/cosmology. This is a new window to observe the beginning and evolution of our universe. In the next few decays, there will be many new gravitational-wave experiments, including the Japanese project KAGRA. This research is aimed to study the general and characteristic features of the stochastic gravitational-wave background originating from different sources in the early universe, which is helpful in both comprehending the physics of the early universe, and in seeking for such signals in the future.
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| Outline of Final Research Achievements |
I completed 13 research papers, of which 10 are already published. The main achievements are as follows. (1) We found a fully nonlinear expression for the curvature perturbation in single-field inflation models, which is very helpful in determining its statistical properties. SP and Sasaki, Phys.Rev.Lett. 131 (2023) 1, 011002. 48 citations. (2) We show that under some general conditions, the GW spectra, no matter what sources they come from, has an universal infrared f^3 scaling. Cai, SP, and Sasaki, Phys.Rev.D 102 (2020) 8, 083528. 141 citations. (3) We show that the nHz GW signal observed by pulsar timing arrays (NANOGrav, etc.) could indicate the presense of planet-mass PBHs. Demenech and SP, Sci.China Phys.Mech.Astron. 65 (2022) 3, 230411. 124 citations.
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| Academic Significance and Societal Importance of the Research Achievements |
この研究は、初期宇宙の謎を解き明かすための重要な進展を遂げました。特に、原初ブラックホールの形成やインフレーション理論の解析において、新たな視点を提供しました。研究者は、曲率摂動の非ガウス性とその統計的性質を明らかにし、ブラックホールの形成率を精密に計算しました。また、これらの計算結果を一般相対性理論の数値シミュレーションで検証し、信頼性を高めました。さらに、次世代の重力波観測（LISAやDECIGO）を通じて、理論的予測と実際の観測データを照らし合わせる試みも行われています。この研究は、宇宙の初期条件や構造形成の理解を深め、現代宇宙論において重要な役割を果たしています。
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