Dr. Kiyoharu Kawana "[CTP Seminar] Can QCD Axion explain the CMB anisotropy?" (Host: Sunghoon Jung)

Thursday 10 Sep 2020, 16:00 → 17:30 ROK

521 (B56)

*Speaker : Dr. Kiyoharu Kawana (Center for Theoretical Physics, SNU)

 

*Abstract :

It is usually believed that the anisotropy of cosmic microwave background (CMB) is explained by the fluctuation of inflaton produced during cosmic inflation. However, this is not an unique scenario. In this talk, I discuss a possibility that the anisotropy is dominantly generated by the primordial fluctuations of QCD axion under a circumstance that inflaton’s perturbation is too small to explain the anisotropy. 

The following conditions must be satisfied in this scenario: (i) sufficient amplitudes of the CMB anisotropy (ii) isocurvature constraint and (iii) non-Gaussianity constraint. By carefully studying those conditions, I show that a large energy fraction \Omega_A of the axion is necessary at the QCD phase transition when the axion-potential is generated, but simultaneously, it must become tiny at the present era due to the isocurvature constraint. 

Thus, an additional scenario of the early universe, such as thermal inflation, is inevitable to dilute the axions. I will also talk such a scenario if time permits.