Chakraborty, S., Gupta, A., & Vanvlasselaer, M. (2024). Photoproduction of heavy QCD axions in supernovae. Phys. Rev. D, 110(6), 063032–13pp.
Abstract: Compact stellar objects like supernovae and neutron stars are believed to cool by emitting axions predominantly via bremsstrahlung (NN -> NNa), pion conversion (pi(-) p(+)-> Na), and photoproduction (gamma N -> Na). In this paper, we study new contributions to the photoproduction channel pertaining to axions. We first point out the impact of anomaly-induced unavoidable Wess-Zumino-Witten term proportional to epsilon(mu nu alpha beta) F-mu nu partial derivative(alpha)a omega(beta) in the photoproduction of such axions. We then perform a complementary data-driven study where the rate of photoproduction can be estimated from low-energy pion photoproduction data. We found that for such heavier axions, i.e., m(a) similar to O(100) MeV, photoproduction processes can be dominant compared to the usual emission processes. In addition, the spectrum of these particles emitted in the process is significantly harder than those originating from bremsstrahlung.
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Chakraborty, S., Gupta, A., & Vanvlasselaer, M. (2023). Anomaly induced cooling of neutron stars: a Standard Model contribution. J. Cosmol. Astropart. Phys., 10(10), 030–23pp.
Abstract: Young neutron stars cool via the emission of neutrinos from their core. A precise understanding of all the different processes producing neutrinos in the hot and degenerate matter is essential for assessing the cooling rate of such stars. The main Standard Model processes contributing to this effect are nu bremsstrahlung, mURCA among others. In this paper, we investigate another Standard Model process initiated by the Wess-Zumino-Witten term, leading to the emission of neutrino pairs via N gamma -> N nu nu over bar . We find that for proto-neutron stars, such processes with degenerate neutrons can be comparable and even dominate over the typical and well-known cooling mechanisms.
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