Exploring dark sector parameters in light of neutron star temperatures

TL;DR

This paper investigates how fermionic dark matter interacting via a dark gauge boson can heat neutron stars through novel annihilation and decay processes, with implications for future observational detection.

Contribution

It introduces a new neutron star heating mechanism involving dark matter annihilation into dark gauge bosons that decay into Standard Model particles, expanding current models.

Findings

Dark matter annihilation into dark gauge bosons can significantly heat neutron stars.

Axial-vector couplings play a notable role in relativistic scattering scenarios.

Future telescopes could detect these dark matter-induced heating effects.

Abstract

Using neutron stars (NS) as a dark matter (DM) probe has gained broad attention recently, either from heating due to DM annihilation or its stability under the presence of DM. In this work, we investigate spin-$1/2$ fermionic DM $\chi$ charged under the $U(1)_{X}$ in the dark sector. The massive gauge boson $V$ of $U(1)_{X}$ gauge group can be produced in NS via DM annihilation. The produced gauge boson can decay into Standard Model (SM) particles before it exits the NS, despite its tiny couplings to SM particles. Thus, we perform a systematic study on $\chi\bar{\chi}\to2V\to4{\rm SM}$ as a new heating mechanism for NS in addition to $\chi\bar{\chi}\to2{\rm SM}$ and kinetic heating from DM-baryon scattering. The self-trapping due to $\chi V$ scattering is also considered. We assume the general framework that both kinetic and mass mixing terms between $V$ and SM gauge bosons are present. This allows both vector and axial-vector couplings between $V$ and SM fermions even for $m_V\ll m_Z$. Notably, the contribution from axial-vector coupling is not negligible when particles scatter relativistically. We point out that the above approaches to DM-induced NS heating are not yet adopted in recent analyses. Detectabilities of the aforementioned effects to the NS surface temperature by the future telescopes are discussed as well.