Speaker
Description
We explore a non-minimal secluded dark sector (DS) within an effective field theory (EFT) framework. We consider a suitable extension of the type-X Two Higgs Doublet Model (2HDM) as the ultraviolet origin of the secluded dark sector. The DS consists of a dark matter (DM) candidate and a mediator particle $a$. It is non-thermally populated through various dimension-6 four-fermion operators, which are effectively generated by integrating out the heavy Higgs bosons of the 2HDM. We investigate the impact of the $2\to 2$ scattering processes $\textit{DM} + a \leftrightarrow a + a$ and $\textit{DM} + \textit{DM} \leftrightarrow a + a$ taking place within the dark sector. Particular emphasis is placed on the importance of adopting an EFT approach to accurately track the temperature evolution of the DS. Within this framework, the observed DM relic abundance can be successfully reproduced through both dark freeze-out and freeze-in mechanisms. Furthermore, by demanding perturbativity of the relevant couplings while simultaneously satisfying the observed relic density, constraints from Big Bang Nucleosynthesis (BBN), and limits from $\gamma$-ray observations, we identify the viable parameter space: $m_\chi \gtrsim 20$ GeV for the DM mass, $C_\tau \lesssim 10^{-14}$ GeV$^{-2}$ for the portal coupling, and $\lambda \lesssim 10^{-6}$ GeV$^{-2}$ for the dark sector coupling.