The 14th International Workshop Dark Side Of the Universe

Observable windows for the QCD axion as a hot relic

Non programmé

20m

Auditorium (Annecy-le-Vieux, France)

Contributed talk Parallel II

Orateur

Alessio Notari

Description

I will discuss the possibility of detecting the QCD axion as a hot relic from the early universe, if it is directly coupled to quarks, such as in DFSZ models. For sufficiently low decay constant the dominant production mechanism at temperatures 1GeV≲T≲100GeV is obtained via scatterings with heavy quarks. This leads to a contribution to the effective neutrino number, $N_eff$, which is larger than the one obtained when thermalization happens only above the electroweak phase transition, ΔNeff≲0.027. Such a prediction is within reach of future CMB S4 experiments, thus opening an alternative window to detect the QCD axion and to test the early universe at such temperatures.