Axion-like particles (ALPs) coupled to nucleons might be copiously emitted from a supernova core.
This work is devoted to the extension of existing bounds on free-streaming ALPs to the case in which these are so strongly-interacting with the nuclear matter to be trapped in the SN core.
From SN 1987A neutrino burst observations, two different arguments have been considered to constrain the ALP parameter space:
the cooling criterium and the absence of an ALP-induced signal in Kamiokande-II neutrino detector. These lead to the exclusion of ALP-nucleon coupling $g_{aN}\gtrsim10^{-9}$ for ALP masses $m_a\lesssim 1\,\mathrm{MeV}$.
Remarkably, in the case of canonical QCD axion models, the SN bounds exclude all values of $m_a \gtrsim 10^{-2} \mathrm{eV}$. This result prevents the possibility for current and future cosmological surveys to detect any signatures due to hot dark matter QCD axion mass.