Cosmic neutrino background radiation

2022 Fiscal Year Final Research Report

• 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
• 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.

Free Research Field

宇宙物理学

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。