Thermally corrected masses and freeze-in dark matter: a case study

If coupled feebly to the Standard Model bath, dark matter can evade the severe constraints from the direct search experiments. At the same time, such interactions help produce dark matter via the freeze-in mechanism. The freeze-in scenario becomes more interesting if one also includes the thermal masses of the different particles involved in the dark matter phenomenology. Incorporating such thermal corrections opens up the possibility of dark matter production via channels that remain kinematically disallowed in the standard freeze-in setup. Motivated by this, we investigate such freeze-in production of the dark matter in a minimally extended U(1)Lμ-Lτ framework, which is also known to resolve the muon g-2 anomaly. Here, the role of the dark matter is played by a scalar with a nontrivial charge under the additional symmetry U(1)Lμ-Lτ. The importance of incorporating the appropriate finite temperature corrections to freeze-in dynamics is aptly demonstrated in this study using the U(1)Lμ-Lτ scenario as a prototype.