We revisit the two real singlet extension of the Standard Model with a $$ {Z}_2\times {Z}_2^{\prime } $$ Z 2 × Z 2 ′ symmetry. One of the singlet scalars S2, by virtue of an unbroken $$ {Z}_2^{\prime } $$ Z 2 ′ symmetry, plays the role of a stable dark matter candidate. The other scalar S1, with spontaneously broken Z2-symmetry, mixes with the SM Higgs boson and acts as the scalar mediator. We analyze the model by putting in the entire set of theoretical and recent experimental constraints. The latest bounds from direct detection Xenon1T experiment severely restricts the allowed region of parameter space of couplings. To ensure the dark matter satisfies the relic abundance criterion, we rely on the Breit-Wigner enhanced annihilation cross-section. Further, we study the viability of explaining the observed gamma-ray excess in the galactic center in this model with a dark matter of mass in the ∼ 36 − 51 GeV window and present our conclusions.
We reinvestigate the two real singlet extension of the Standard Model with a Z 2 × Z 2 ′ symmetry. In this model, the destructive interference between the two t-channel scalar mediators to some extent alleviates the otherwise very stringent constraint from the Xenon1T experiment while the Breit-Wigner enhancement of dark matter annihilation cross section not only proves useful in satisfying the relic abundance criterion but also ensures the scope for explaining the observed gamma-ray excess in the galactic centre.
The Littlest Seesaw model is a very well motivated dark matter model. Here we consider an extension of that model with an additional scalar and an additional fermionic particle under the freeze-in scenario. Formation of black hole of a certain mass range at primordial times can act as an alternate production mechanism for the dark matter particles as it evaporates via Hawking radiation. Furthermore, the presence of primordial black holes with substantial energy density gives rise to non-standard cosmology which also modifies the freeze-in production. In this paper, we have investigated the extended Littlest Seesaw model under the freeze-in scenario in the presence of a primordial black hole for various interesting cases and constrained the parameter space accordingly. If the universe is primordial black hole dominated at any point in the evolution of the universe, we find that the final relic in that case is dominated mostly by the evaporation component for a high dark matter mass and by the freeze-in component for a low dark matter mass.
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