Speaker
Description
In this work, we address the impact of the thermal Debye mass 𝑚𝐷 scale on the bound-state formation and ionization (dissociation) in the dark sector in the Early Universe. We focus on heavy dark fermions (with mass 𝑚) charged under a 𝑈(1)𝑑 group coupling dark matter to dark photons and dark light fermions with the coupling constant 𝛼=𝑔2/4𝜋. We determine the effect of the HTL resummation on the bound-state formation and dissociation rates of heavy dark fermions in presence of a hot (with temperature 𝑇), weakly coupled (𝑇≫𝑔𝑇) dark plasma, under the assumption that 𝑚≫𝑚𝛼≫𝑇. Our analysis is based on Non-Relativistic Effective Field Theory (NREFT) to address the dark matter threshold dynamics and on Thermal Field Theory to address the thermal scales. We obtain and solve coupled Boltzmann equations and show how our results affect the evolution of the dark matter density in the Early Universe. Working with this simplified model of the dark sector, we show that the effect of HTL resummation on the bound-state formation and thermal relic abundance is non-negligible (and of the same order as the NLO fixed order correction), which indicates the importance of further studies in more realistic scenarios. This, to our knowledge, is the first study of the impact of the scale 𝑚𝐷 on dark matter scattering and bound states formation in a systematic framework.