CMB signature of non-thermal Dark Matter produced from self-interacting dark sector

Abstract

The basic idea of this work is to achieve the observed relic density of a non-thermal dark matter(DM) and its connection with Cosmic Microwave Background (CMB) viaadditional relativistic degrees of freedom which are simultaneously generated duringthe period T BBN to TCMB from a long-lived dark sector particle.To realize this phenomena we minimally extend the type-I seesaw scenario with a Diracfermion singlet(χ) and a complex scalar singlet (φ) which transformnon-trivially under an unbroken symmetry Z̶ 3. χ being the lightestparticle in the dark sector acts as a stable dark matter candidate while the next tolightest state φ operates like a long lived dark scalar particle. The initialdensity of φ can be thermally produced through either self-interacting numberchanging processes (3φ ⟶ 2φ) within dark sector or the standardannihilation to SM particles (2φ ⟶ 2 SM).The late time (after neutrino decoupling) non-thermal decay of φ can producedark matter in association with active neutrinos. The presence of extrarelativistic neutrino degrees of freedom at the time of CMB can have asignificant impact on ΔNeff. Thus the precise measurement ofΔNeff by current PLANCK 2018 collaboration and future experimentslike SPT-3G and CMB-S4 can indirectly probe this non-thermal dark matter scenariowhich is otherwise completely secluded due to its tiny coupling with the standardmodel.