Speaker
Description
The fundamental nature of dark matter (DM) and its production mechanism is yet unknown. Non thermal or freeze in DM scenarios are currently being widely explored. In this work we explore the production of non-thermal DM and its connection with Cosmic Microwave Background (CMB) via additional relativistic degrees of freedom which are simultaneously generated during the period $T_{\rm BBN}$ to $T_{\rm CMB}$ from a long-lived dark sector particle. To realize this phenomena we minimally extend the type-I seesaw scenario with a Dirac fermion singlet($\chi$) and a complex scalar singlet ($\phi $) which transform non-trivially under an unbroken symmetry $Z_3$. $\chi$ being the lightest stable particle in the dark sector, acts as a stable dark matter candidate while the next to lightest state $\phi $ operates like a long lived dark scalar particle. The initial density of $\phi$ is thermally generated through either self-interacting number
changing processes (3$\phi \to 2 \phi $ ) within dark sector or the standard annihilation to SM particles (2$\phi \to $ 2 SM). The late time (after neutrino decoupling) non-thermal decay of $\phi $ can produce dark
matter in association with active neutrinos. The presence of extra relativistic neutrino degrees of freedom at the time of CMB can have a significant impact on $\Delta N_{\rm eff}$. Thus the precise measurement of $\Delta N_{\rm eff}$ by current PLANCK 2018 collaboration and future experiments like SPT-3G and CMB-S4 can indirectly probe this non-thermal dark matter scenario which is otherwise completely secluded due to its tiny coupling with the standard model
