Improved hot dark matter bound on the QCD axion

Alessio Notari, Fabrizio Rompineve, Giovanni Villadoro

Submitted on 7 November 2022


We strengthen the cosmological bound on the axion mass, by solving the momentum-dependent Boltzmann equations for axion-pion scatterings and by using a phenomenological production rate derived from pion-pion scattering data, overcoming the breakdown of chiral perturbation theory. Using present cosmological datasets we obtain ma0.24 eV. To further improve the bound and exploit the reach of upcoming cosmological surveys, reliable non-perturbative calculations above the QCD crossover are needed.


Comment: 6+8 pages, 7 figures

Subjects: High Energy Physics - Phenomenology; Astrophysics - Cosmology and Nongalactic Astrophysics


Scattering rates for $a\pi \leftrightarrow \pi\pi$ (solid curves for phenomenological rates, dashed for LO in $\chi$PT). {\it Left:} momentum dependent axion destruction rates  at $T=120$ MeV. {\it Right:} Averaged rates.