Speaker
Description
Axion-like particles (ALPs) decaying before the time of recombination can have
strong implications in a range of cosmological and astrophysical observations. In this
talk I present a global analysis of a model of decaying ALP, focusing specifically on their
coupling to photons. Exploiting the multidisciplinary nature of the GAMBIT frame-
work, we combine state-of-the-art calculations of the irreducible ALP freeze-in abun-
dance, primordial element abundances (including photodisintegration through ALP
decays), CMB spectral distortions and temperature anisotropies, and astrophysical
constraints from supernovae and stellar cooling. Most notable among the interesting
results that I will present are a definite lower bound on the ALP mass, and a surprising
improvement of the fit to the primordial abundances compared to vanilla ΛCDM.
