Millicharged Particle Production During Late-Stage Stellar Evolution

Stars are natural sources of feebly interacting particles, including putative particles with mass $m_\chi$ and electric charge $qe$. The emission of such millicharged particles (MCPs) causes an energy loss which can alter stellar evolution. While MCP production rates have been computed for different plasma parameters, they have yet to be derived for the conditions relevant to late stages of stellar evolution, in which the temperature can reach values $T\simeq 10-100\,\rm keV$ while the plasma frequency is $\omega_{\rm pl}\ll T$. In this paper, we compute the MCP energy-loss rates relevant for pre-supernova objects, finding three different regimes in which the dominant processes are respectively plasmon decay ($m_\chi< \omega_{\rm pl}/2$), Compton-like scattering ($m_\chi> \omega_{\rm pl}/2$, $T\lesssim 0.5\,\rm MeV$), and electron-positron annihilation. We obtain semi-analytical fits for the energy-loss rates suitable for implementation in stellar evolution codes.