We review the landscape of QCD axion models. Theoretical constructions that extend the
window for the axion mass and couplings beyond conventional regions are highlighted and …

We review several current aspects of dark matter theory and experiment. We overview the
present experimental status, which includes current bounds and recent claims and hints of a …

Various pulsar timing array (PTA) experiments (NANOGrav, EPTA, PPTA, CPTA, including
data from InPTA) very recently reported evidence for excess red common-spectrum signals …

We revisit the possibility that the stochastic common-spectrum process recently detected by
the NANOGrav pulsar timing array experiment could be due to primordial gravitational …

The NANOGrav pulsar timing array experiment reported evidence for a stochastic common-
spectrum process affecting pulsar timing residuals in its 12.5-yr data set, which might be …

It is commonly assumed that the energy density of the Universe was dominated by radiation
between reheating after inflation and the onset of matter domination 54,000 years later …

The effective number of relativistic neutrino species is a fundamental probe of the early
Universe, and its measurement represents a key constraint on many scenarios beyond the …

Abstract If the Peccei-Quinn symmetry associated to an axion has ever been restored after
inflation, axion strings inevitably produce a contribution to the stochastic gravitational wave …

We consider the production of matter and radiation during reheating after inflation, restricting
our attention solely to gravitational interactions. Processes considered are the exchange of a …

We consider the direct s-channel gravitational production of dark matter during the reheating
process. Independent of the identity of the dark matter candidate or its nongravitational …