Speaker
Description
Axion-like particles (ALPs) are among the most promising dark matter candidates. Yet a large part of parameter space, in particular the regime of large decay constants where ALPs become effectively invisible, remains difficult to probe experimentally. In the supercooled audible axion mechanism, invisible ALPs can generate a sizable primordial gravitational wave (GW) background via a tachyonic resonance induced by their coupling to photons. I will discuss the conditions under which this resonance develops, the resulting GW spectrum, and the associated production of large-scale magnetic fields. Remarkably, parameter regions that yield pronounced GW signals in the $\mu$Hz band can simultaneously account for the intergalactic magnetic fields suggested by recent blazar observations.