Dark matter and thermal pulses in horizontal-branch stars

Abstract

The evolution of horizontal-branch (HB) stars, including the effect of energy transfer by dark matter particles ('WIMPs' or 'cosmions') is investigated numerically. If HB stars contain enough cosmions to break core convection, thermal pulses ensue on the core Kelvin-Helmholtz time scale until the central helium abundance is exhausted. These pulses involve brief phases of violent helium burning which establish short episodes of convection where the convective core extends further than it would in the absence of cosmions. The overall duration of the HB phase slightly decreases, and the luminosity dispersion of the HB increases, but neither effect is pronounced enough to conflict with observations. The magnitude difference between the HB and the main-sequence turnoff increases and leads to an overestimate of globular cluster ages. The observed period changes of RR Lyrae stars are consistent with, and even implied by, this scenario.