Seminars IFIC

IFIC Seminar: Cosmological probes of the QCD axion -- CMB and gravitational waves

by Dr. Ricardo Z. Ferreira (IFAE, Barcelona)

1001-Primera-1-1-1 - Paterna. Seminario (Universe)

1001-Primera-1-1-1 - Paterna. Seminario



In this talk I will discuss how to probe the QCD axion through the cosmic microwave background (CMB) and gravitational wave observatories.

Future CMB experiments will be able probe the number of effective degrees of freedom (Neff) with great precision. If the QCD axion is able to thermalise with the primordial plasma at temperatures below the electroweak phase transition, it will then decouple and leave a bath of hot relics that can leave a detectable impact on Neff.  I will overview the different channels through which the axion can thermalise with the Standard Model bath and show that in the case of tree-level scatterings with SM fermions the prospects are quite promising.

Finally, I will discuss some recent work where we have shown that heavy QCD axion models, motivated by the so-called quality problem, despite the absence of relics can produce correlated signals at GW observatories and future neutron and proton EDM experiments.

IFIC seminar organizers
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