宇宙素粒子物理学

宇宙から飛来する宇宙線、ガンマ線、ニュートリノなどを観測し、宇宙における高エネルギー天体現象や、暗黒物質などの素粒子物理を研究する分野を宇宙素粒子物理学（Astroparticle Physics）と呼ぶ。この分野の歴史的な成果として、CP対称性を破るK中間子などの新粒子の発見、最高エネルギー宇宙線の発見、ガンマ線バーストやブレーザーなどのブラックホール起源ガンマ線の検出、ニュートリノ振動の発見などが挙げられる。近年の観測技術の向上により、複数の観測手段を組み合わせて議論するマルチメッセンジャー天文学の時代となり、著しい発展を見せている分野である。この講義では、宇宙における高エネルギー粒子の起源や、それらの物理的性質、観測原理について基礎的なところから学ぶことを目標とする。講義内容については以下の英語版を参照。大きく3つに分かれている。

なお、この分野の最新成果についてはオムニバス形式の授業「天体素粒子物理学特論II」でカバーされるので、そちらも受講することが望ましい。

Astroparticle physics is a research field that studies high-energy astronomical phenomena and particle physics including dark matter via observations of cosmic rays, gamma-rays, neutrinos and so on. Some of representative discoveries done in this field are new particles such as kaon, which shows CP violation, ultra-high-energy cosmic rays, gamma-rays from black holes like gamma-ray bursts and blazars, and neutrino oscillation. Recent progress in the detector technology leads us to the era of multi-messenger astronomy, which is astronomy via collaborative observations of different species of particles. So this research field has been greatly developed in this decade. The purpose of this lecture is learning basics of origins of high-energy particles, physical properties of particles, and detection technique. The contents are divided into three parts as follows.

１．Origin of High-energy Particles
High-energy particles are accelerated somewhere in the universe, and produce secondary particles via interacting with other particles. Sources and the production mechanisms of such particles are not yet revealed, so numerous models have been proposed. In this lecture, we learn Fermi acceleration at shock waves as a promising particle acceleration mechanism, cosmic ray propagation in the interstellar medium, and emission mechanisms of gamma-rays and neutrinos. We also learn high-energy astrophysical phenomena as particle production sites.

２．Neutrino Physics
Neutrinos have long been assumed to be massless, and the Standard Model of particle physics, based on this assumption, has been established as the paradigm that explains the results of many experiments to a high degree of accuracy. In 1998, however, it was discovered that neutrinos have finite mass and come in different flavors. The assumptions of the Standard Model turned out to be wrong, and this had a major impact on our understanding of particle physics and the nature. In this lecture, we will discuss the fundamental properties of neutrinos, their experimental verification mainly by neutrino oscillations, and the remaining unknowns and future experiments.

３．Dark Matter
　The mystery of dark matter is one of the most critical issues in cosmology and particle physics because it plays a leading role in shaping the universe and its potential to interrelate with various problems in particle physics. There are three main approaches to the experimental verification of dark matter: accelerator generation, indirect detection by observing signals from the decay and the annihilation of dark matter in space, and direct detection by capturing events in which dark matter around us collides with detectors. Research to elucidate the nature of dark matter is being actively pursued using all of these approaches. In this lecture, we will discuss various dark matter candidates and the principles and current status of direct and indirect search experiments for them.

The latest observational results in astroparticle physics are presented by omnibus lectures in the course “Advanced Astroparticle Physics I”. We recommend to attend that course as well.