Cosmic neutrino background radiation

Research Project

Project/Area Number	18K18764
Research Category	Grant-in-Aid for Challenging Research (Exploratory)
Allocation Type	Multi-year Fund
Review Section	Medium-sized Section 15:Particle-, nuclear-, astro-physics, and related fields
Research Institution	Tokyo Institute of Technology
Principal Investigator	Yamaguchi Masahide 東京工業大学, 理学院, 特定教授 (80383511)
Project Period (FY)	2018-06-29 – 2023-03-31
Project Status	Completed (Fiscal Year 2022)
Budget Amount *help	¥5,460,000 (Direct Cost: ¥4,200,000、Indirect Cost: ¥1,260,000) Fiscal Year 2020: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000) Fiscal Year 2019: ¥2,080,000 (Direct Cost: ¥1,600,000、Indirect Cost: ¥480,000) Fiscal Year 2018: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000)
Keywords	ニュートリノ
Outline of Final Research Achievements	We studied the decoupling process of neutrinos in the early universe. The evolution of the distortion of the neutrino spectrum in both the mass and flavor bases is calculated, and the effect of QED finite temperature corrections up to O(e cubed) on the associated equations of motion is also incorporated for the first time. As a result, we show that the effective number of neutrinos is given by Neff =3.044. We also discussed experiments that use neutrino capture by tritium to observe cosmic neutrino background. In particular, we evaluated the exact capture rate for each neutrino species, including cosmological effects such as neutrino decoupling and neutrino clustering in the galaxy.
Academic Significance and Societal Importance of the Research Achievements	素粒子標準模型からの逸脱の鍵であり、また、宇宙初期の状態を探る新しい窓ともなるニュートリノ、特に、ニュートリノ背景放射について、その存在量をこれまでにない精度で見積もり、また、その捕獲率を評価したことは、上記の目的にとって大きな進展となり学術的な意義があったといえます。