Abstract
We discuss the dark gauge boson emission from neutron stars via nucleon-nucleon bremsstrahlung. Through the rigorous treatment of the effective field theory prescription and the thermal effect, we derive the relevant couplings of dark gauge bosons to hadrons in medium. As a specific example, the U(1)B−L gauge boson scenario is chosen to investigate dark gauge boson emissivities during supernovae and cooling of young neutron stars. From the stellar cooling argument, we obtain the constraints on the B − L gauge coupling for given gauge boson masses in two observations: the duration of the supernova neutrino signal of SN1987A, and the inferred x-ray luminosity of the compact object in the remnant of SN1987A (NS1987A). In particular, the constraint from SN1987A on the U(1)B−L gauge boson scenario is revisited. The excluded gauge coupling due to the emission of transverse polarizations is an order of magnitude enhanced compared to the previous derivation. There is also a newly excluded parameter space due to the emission of longitudinal polarizations.
Highlights
Through the rigorous treatment of the effective field theory prescription and the thermal effect, we derive the relevant couplings of dark gauge bosons to hadrons in medium
We find the relevant couplings to hadrons for nucleon-nucleon bremsstrahlung, based on the symmetry argument with chiral perturbation theory
We have discussed the production of dark gauge bosons via nucleon-nucleon bremsstrahlung from NS with considering their effective couplings to hadrons concretely in the context of the Chiral Perturbation Theory (ChPT) and the thermal field theory framework
Summary
We notice that the in-medium mixing between Aμ and Aμ [20] could make an impact on effective couplings of dark gauge bosons. In order to account for the plasma effect properly (and a kinetic mixing via ε), we have to appreciate a peculiar dispersion relation of electromagnetic excitations in the medium [49–51]. Because a dominant contribution to the dispersion relation is given by electrons, the lightest charged particles, we can approximate the effective coupling to the SM particle f in medium as f efeff Aμfγμf with We focus on the specific dark U(1) gauge boson scenario that dark gauge bosons couple to the anomaly-free B − L current, where B and L denote the baryon and lepton number charge, respectively. As we will discuss later, this isospin breaking combination leads to enhancement of the emission rate of U(1)B−L gauge bosons in the context of an expansion of the order parameter
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