Goldstone Boson Emission From Nucleon Cooper Pairing in Neutron Stars and Constraints on the Higgs Portal Models

TL;DR

This paper investigates how neutron star cooling via nucleon pair-breaking processes can constrain Higgs portal models involving Goldstone bosons, extending astrophysical limits on dark radiation interactions.

Contribution

It applies neutron star PBF neutrino emission constraints to Weinberg's Higgs portal model, exploring new parameter space for dark radiation interactions.

Findings

PBF processes can probe Higgs portal interactions in neutron stars.

Astrophysical constraints complement laboratory experiments.

Results extend bounds on dark radiation from superfluid neutron star models.

Abstract

When a neutron star cools to below the critical temperature for the onset of superfluidity, nucleon pair breaking and formation (PBF) processes become the dominant mechanism for neutrino emission, while the modified URCA and the nuclear bremsstrahlung processes are suppressed. The PBF processes in neutron stars have also been used to set upper limits on the properties of axions, which are comparable to those set by supernova SN 1987A. We apply this constraint on Weinberg's Higgs portal model, in which the dark radiation particles (the Goldstone bosons) and the dark matter candidate (a Majorana fermion) interact with the Standard Model (SM) fields solely through the mixing of the SM Higgs boson and a light Higgs boson. We compare the Goldstone boson emissivity with that of the neutrinos by considering several superfluid gap models for the neutron singlet-state pairing in the neutron star inner crust, as well as in the core region. We find that the PBF processes in the superfluid neutron star interior can indeed probe Weinberg's Higgs portal model in a new parameter space region. Together with our previous works on the constraints from supernovae and gamma-ray bursts, this study demonstrates further the competitiveness and complementarity of astrophysics to laboratory particle physics experiments.