Anomaly Induced Supernovae Cooling: New Contribution from Axions

Compact stellar objects like supernovae and neutron stars are believed to cool by emitting axions predominantly via axion bremsstrahlung (NN → NNa), pion conversion (π⁻ p⁺ → N a) and photo-production (γ N → N a). In this letter, we study a previously overlooked contribution to the photo-production channel, originating from the unavoidable anomaly-induced Wess-Zumino-Witten term ∝ εμ ν α β\, Fμ ν\, ∂_α a \, ω_β. As a result, supernovae can cool up to three times faster than what was previously thought, translating into stronger bounds on the axion decay constant. Furthermore, the spectrum of axions emitted in the process is unique as it is significantly harder than those originating from bremsstrahlung. As a consequence, we find that these axions are more likely to show up in near future water Cherenkov detectors as compared to traditional ones.