Abstract
We examine the axion emission from supernovae with a complete set of relevant axion couplings including the axion-pion-nucleon contact interaction which was ignored in the previous studies. Two processes are affected by the axion-pion-nucleon contact interaction, π− + p → n + a and n + p → n + p + a, and these processes can be the dominant source of axions for some region in the axion parameter space or in astrophysical conditions encountered inside supernovae. We find that the contact interaction can enhance the axion emissivity of π− + p → n + a by a factor of 2 − 4, while the effect on n + p → n + p + a is not significant. We also discuss the relative importance of other pion-induced processes such as π0 + n → n + a and π− + π0→ π− + a.
Highlights
For many years [24,25,26,27,28]
We find that π0 + n → n + a can be as important as π− + p → n + a, again depending on the pattern of axion couplings, while π− + π0 → π− + a is negligible compared to π− + p → n + a over the entire axion parameter space for astrophysical conditions encountered inside proto-neutron stars
A recent study suggests that the abundance of negatively charged pions inside supernovae is significantly enhanced by the strong interactions [29], indicating that the pion-induced process π− +p → a+n is the dominating process for a wide range of astrophysical conditions encountered inside supernovae [32, 33]
Summary
We briefly discuss the axion couplings to nucleons and pions for generic axions whose couplings are constrained only by the (approximate) global U(1) PecceiQuinn (PQ) symmetry [1,2,3,4]. The axion-gluon coupling cG, which arises as a consequence of the axion-dependent field redefinition of ψ, corresponds to the coefficient of the U(1)PQ-SU(3)c-SU(3)c anomaly, while the couplings Cu,d to the light quarks are determined by (i) a contribution from the axion-dependent fieldredefinition of {Q1, uc, dc1}, (ii) the tree-level threshold correction from the axion mixing with the Z boson which is induced by the field redefinition of Hu,d, and (iii) the radiative corrections caused by the gauge and Yukawa couplings in the model [36].
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