Fazlollah Hajkarim (University of Padua, INFN)
We study the production of relativistic relics, also known as dark radiation, in the early Universe and precisely compute their current contribution to the extra number of effective neutrinos. One of the dark radiation candidates is the QCD axion produced from the primordial bath in the early universe. We consider KSVZ and DFSZ axion models and investigate the axion production at different scales. The dark radiation from QCD axion leaves an imprint on the observed cosmic microwave background that can be measured by the CMB-S4 experiment.
Fazlollah Hajkarim (University of Padua, INFN) Francesco D'Eramo (University of Padua, INFN) Seokhoon Yun (University of Padua, INFN)