QCD axion: Some like it hot

We compare the quantum chromodynamics (QCD) axion phase-space distribution from unitarized next-to-leading order chiral perturbation theory with the one extracted from pion-scattering data. We derive a robust bound by confronting momentum-dependent Boltzmann equations against up-to-date observations of the cosmic microwave background, of the baryonic acoustic oscillations and of primordial abundances. These datasets imply 𝑚_𝑎 ≤ 0.16 eV for the 95% credible interval, i.e., ∼ 30% stronger bound than what previously found. We present forecasts using dedicated likelihoods for future cosmological surveys and the sphaleron rate from unquenched lattice QCD.. Authors: Bianchini, Federico [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford Univ., CA (United States). Kavli Institute for Particle Astrophysics & Cosmology] (ORCID:0000000348473483); di Cortona, Giovanni Grilli [National Inst. of Nuclear Physics (INFN), Rome (Italy)] (ORCID:0000000324086171); Valli, Mauro [National Inst. of Nuclear Physics (INFN), Rome (Italy)] (ORCID:0000000208993735). DOE Contract: AC02-76SF00515. Subjects: Big bang nucleosynthesis; Cosmic microwave background; Cosmological parameters; Large scale structure of the Universe; Particle dark matter