We study the impact of thermalization and number-changing processes in the dark sector on the yield of gravitationally produced dark matter (DM). We take into account the DM production through the s-channel exchange of a massless graviton both from the scattering of inflatons during the reheating era, and from the Standard Model bath via the UV freeze-in mechanism. By considering the DM to be a scalar, a fermion, and a vector boson we show, in a model-independent way, that DM self-interaction gives rise to a larger viable parameter space by allowing lower reheating temperature to be compatible with Planck observed relic abundance. As an example, we also discuss our findings in the context of the ℤ₂-symmetric scalar singlet DM model.

We propose a novel way of probing high-scale Dirac leptogenesis, a viable alternative to the canonical leptogenesis scenario where the total lepton number is conserved, keeping light standard model neutrinos purely Dirac. The simplest possible seesaw mechanism for generating light Dirac neutrinos involves heavy singlet Dirac fermions and a singlet scalar. In addition to unbroken global lepton number, a discrete $Z_2$ symmetry is imposed to forbid direct coupling between right and left chiral parts of light Dirac neutrinos. Generating light Dirac neutrino mass requires the singlet scalar to acquire a vacuum expectation value (VEV) that also breaks the $Z_2$ symmetry, leading to the formation of domain walls in the early Universe. These walls, if made unstable by introducing a soft $Z_2$-breaking term, generate gravitational waves (GWs) with a spectrum characterized by the wall tension or the singlet VEV, and the soft symmetry breaking scale. The scale of leptogenesis depends on the $Z_2$-breaking singlet VEV, which is also responsible for the tension of the domain wall, affecting the amplitude of GWs produced from the collapsing walls. We find that most of the near-future GW observatories will be able to probe Dirac leptogenesis scales all the way up to ${10}^{11}\mathrm{GeV}$.

We show that a minimal scenario, utilizing only the graviton as an intermediate messenger between the inflaton, the dark sector and the Standard Model (SM), is able to generate simultaneously the observed relic density of dark matter (DM), the baryon asymmetry through leptogenesis, as well as a sufficiently hot thermal bath after inflation. We assume an inflaton potential of the form V(ϕ) ∝ ϕ^k about the minimum at the end of inflation. The possibility of reheating via minimal gravitational interactions has been excluded by constraints on dark radiation for excessive gravitational waves produced from inflation. We thus extend the minimal model in several ways: i) we consider non-minimal gravitational couplings — this points to the parameter range of DM masses $$ {M}_{N_1} $$M N 1 ≃ 2–10 PeV, and right-handed neutrino masses $$ {M}_{N_2} $$M N 2 ≃ (5–20) × 10¹¹ GeV, and T_RH ≲ 3 × 10⁵ GeV (for k ≤ 20); ii) we propose an explanation for the PeV excess observed by IceCube when the DM has a direct but small Yukawa coupling to the SM; and iii) we also propose a novel scenario, where the gravitational production of DM is a two-step process, first through the production of two scalars, which then decay to fermionic DM final states. In this case, the absence of a helicity suppression enhances the production of DM and baryon asymmetry, and allows a great range for the parameters including a dark matter mass below an MeV where dark matter warmness can be observable by cosmic 21-cm lines, even when gravitational interactions are responsible for reheating. We also show that detectable primordial gravitational wave signals provide the opportunity to probe this scenario for T_RH ≲ 5 × 10⁶ GeV in future experiments, such as BBO, DECIGO, CE and ET.

In this article, we have considered an extension of the inert Higgs doublet model with $SU(2{)}_L$ singlet vectorlike fermions. Our model is capable of addressing some interesting anomalous results in $b\to s{\ell }^{+}{\ell }^{-}$ decays [like $R(K^{(*)})$] and in muon ($g-2$). Apart from explaining these anomalies, and being consistent with other flavor data, the model satisfies relevant constraints in the dark matter sector, while remaining within the reach of ongoing direct detection experiments. The model also produces signatures at the large hadron collider (LHC) with final states comprised of dilepton, dijet and missing energy, providing signals to be probed at higher luminosity.

We study a minimal scenario to realize nonthermal leptogenesis and UV freeze-in of a Standard Model (SM) gauge singlet fermionic dark matter (DM) simultaneously, with inflaton field playing a nontrivial role in their yields. The renormalizable interactions are restricted to the SM fields, two right-handed neutrinos (RHN) and inflaton coupling exclusively to the RHNs, while the DM couples to both the SM and the RHNs only via operators of dimension $d>4$. Considering two separate cases of $d=\{5,6\}$, we show that for $d=5$, inflaton decay into RHNs followed by their subsequent decay into SM particles lead to both reheating as well as DM production from the SM bath. This requires a cut off scale as large as $\mathrm{\Lambda }\sim {10}^{17}\mathrm{GeV}$ depending on the DM mass. On the other hand, for $d=6$, DM production happens directly from scattering of RHNs (for $\mathrm{\Lambda }\gtrsim {10}^{14}\mathrm{GeV}$) that results in a very nontrivial evolution of the DM yield. In both these cases, it is possible to explain the observed baryon asymmetry through successful nonthermal leptogenesis via the decay of the RHNs, together with the Planck observed relic density of the DM via pure UV freeze-in mechanism. Taking into account both instantaneous as well as noninstantaneous reheating separately, we constrain the parameter space of this minimal scenario from relevant phenomenological requirements including sub-eV scale active neutrino masses and their mixing.

We explore the possibility of explaining the observed dark matter (DM) relic abundance, along with matter-antimatter asymmetry, entirely from the evaporation of primordial black holes (PBH) beyond the semi-classical approximation. We find that, depending on the timing of modification to the semi-classical approximation and the efficiency of the backreaction, it is possible to produce the correct DM abundance for PBHs with masses ≳????(10³) g, whereas producing the right amount of baryon asymmetry requires light PBHs with masses ≲????(10³) g, satisfying bounds on the PBH mass from the Cosmic Microwave Background and Big Bang Nucleosynthesis. However, in a simplistic scenario, achieving bothsimultaneouslyis not feasible, typically because of the stringent Lyman-αconstraint on warm dark matter mass. In addition to DM and baryon asymmetry, we also investigate the impact of memory burden on dark radiation, evaporated from PBH, constrained by the effective number of relativistic degrees of freedom ΔN_eff. Furthermore, we demonstrate how induced gravitational waves from PBH density fluctuations can provide a window to test the memory-burden effects, thereby placing constraints on either the DM mass scale or the scale of leptogenesis.