Breakdown of chiral perturbation theory for the axion hot dark matter bound
Abstract
We show that the commonly adopted hot dark matter (HDM) bound on the axion mass $m_a \lesssim$ 1 eV is not reliable, since it is obtained by extrapolating the chiral expansion in a region where the effective field theory breaks down. This is explicitly shown via the calculation of the axionpion thermalization rate at the nexttoleading order in chiral perturbation theory. We finally advocate a strategy for a sound extraction of the axion HDM bound via lattice QCD techniques.
 Publication:

arXiv eprints
 Pub Date:
 January 2021
 arXiv:
 arXiv:2101.10330
 Bibcode:
 2021arXiv210110330D
 Keywords:

 High Energy Physics  Phenomenology;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 High Energy Physics  Lattice
 EPrint:
 7 pages, 4 figures. Title changed. To appear in Physical Review Letters