Tests of gravity through the fifth force

2021 Fiscal Year Final Research Report

• Project/Area Number: 17K14286
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Particle/Nuclear/Cosmic ray/Astro physics
• Research Institution: Yamaguchi University
• Principal Investigator: Saito Ryo 山口大学, 大学院創成科学研究科, 助教 (70781392)
• Project Period (FY): 2017-04-01 – 2022-03-31
• Keywords: 重力理論 / 第５の力 / 宇宙マイクロ波背景放射 / 背景重力波

Outline of Final Research Achievements

The origin of the cosmic acceleration is one of the biggest challenge in cosmology. One possibility is that Einstein's gravity is not correct on cosmological scales. To test this possibility, we focused on an extra force, "fifth force", as a universal feature in modified gravity theories and investigated its environmental dependence. In parallel, we developed new systematic approaches to accurately compute anisotropies in cosmic microwave background (CMB) and stochastic gravitational-wave background, which are important probes for the cosmic evolution and the gravity theory describing it. Applying this approach to CMB B-mode polarization, we estimated B-mode polarization induced by gravitational effects in photon propagation.

Free Research Field

宇宙論

Academic Significance and Societal Importance of the Research Achievements

重力は我々にとって身近な力であるとともに、宇宙の進化において重要な役割を果たす。本研究の成果は、重力を記述する基礎理論を調べるために必要となるツールを与える。特に本研究の中で開発を行ったcurve-of-sight法は、重力の効果に限らず、宇宙マイクロ波背景放射を系統的に計算する枠組みを与えるものである。重力理論の検証にとどまらず、例えばBモード偏光観測によるインフレーション検証の際に障害となる非線形Bモードの除去など、広い応用が期待される。