Graduate Student Seminar with Takuya Okawa on The Axion

The axion is a hypothetical particle that could solve some remaining problems of the standard model, which successfully describes our universe after the first 10^{-30} second. I will discuss two astrophysical phenomena that possibly prove the existence of axions. 

The axion has been intensively searched because of its possibility to address three major problems in physics: the Strong CP problem, dark matter in the universe, and the matter-antimatter asymmetry problem. We recently proposed two possible ways to detect axions. Firstly, photons with a frequency equivalent to one-half of the axion mass can induce its decay into two photons. Half of the produced photons generate a potentially detectable 'gegenschein' radio signal traveling in the opposite direction. Secondly, axions can be produced inside stars via the Primakoff process and photon coalescence, and subsequently, decay into two photons. Future MeV gamma-ray telescopes such as the APT might be able to detect those photons.