We re-examine the very stringent limits on the axion mass based on the strength and duration of the neutrino signal from SN 1987A , in the light of new measurements of the axial-vector coupling strength of nucleons , possible suppression of axion emission due to many-body effects , and additional emission processes involving pions .
The suppression of axion emission due to nucleon spin fluctuations induced by many-body effects degrades previous limits by a factor of about 2 .
Emission processes involving thermal pions can strengthen the limits by a factor of 3–4 within a perturbative treatment that neglects saturation of nucleon spin fluctuations .
Inclusion of saturation effects , however , tends to make the limits less dependent on pion abundances .
The resulting axion mass limit also depends on the precise couplings of the axion and ranges from 0.5 \times 10 ^ { -3 } { eV } to 6 \times 10 ^ { -3 } { eV } .