Inflaton portal to a highly decoupled EeV dark matter particle

Abstract

We explore the possibility that the dark-matter relic abundance is generated in a context where the inflaton is the only mediator between the visible and the hidden sectors of our universe. Due to the relatively large mass of the inflaton field, such a portal leads to an extremely feeble interaction between the dark and the visible sectors suggesting that the dark sector cannot reach any thermal equilibrium with the visible sector. After the two sectors are populated by the decay of the inflaton, a heavy dark-matter particle thermally decouples within the dark sector. Later, a lighter dark particle, whose decay width is naturally suppressed by the inflaton propagator, decays into the visible sector after it dominates the energy density of universe. This process dilutes the dark-matter relic density by injecting entropy in the visible sector. We show that an inflaton mass of O(10 13 ) GeV together with couplings of order one are fully compatible with a dark-matter relic abundance Ωh 2 ∼ 0.1. As a general feature of the model, the entropy dilution mechanism is accompanied by a period of early matter domination, which modifies the amount of e-folds of inflation necessary to accommodate Planck data. Moreover, the coupling of the inflaton to the dark and visible sectors brings loop contributions to the inflationary potential which can destabilize the inflation trajectory. Considering all these complementary constraints, we show that, in the context of a plateau-inflation scenario such as the α-attractor model, the inflaton can constitute a viable mediator between the visible sector and a ∼ 10 EeV dark-matter candidate. Furthermore, we show that improved constraints on the tensor-to-scalar ratio and spectral index could potentially rule out dark-matter scenarios of this sort in the future. *

Freeze-in dark matter from secret neutrino interactions

“…While in thermal equilibrium, the dark-sector energy density is only a function of the dark-sector temperature T D once the masses of χ and φ are fixed. Therefore, at every step of the numerical simulation, T D can be obtained by solving 17) in which ξ χ = 2 and ξ φ = 1 are the number of degrees of freedom for χ and φ. After obtaining the time dependence of the dark sector temperature T D (t), one can then insert it back to eq.…”

“…For instance, models from the non-minimal dark-sector framework often depend on the collective behavior of an entire ensemble of dark-sector particles [10][11][12]. One could also modify the standard Λ cold dark matter (ΛCDM) cosmology and consider dark-matter production in non-standard cosmologies, such as producing thermal dark matter during a matter dominated universe before the Big-Bang Nucleosynthesis (BBN), see [13,14] for reviews and [15][16][17] for recent progress. By considering different possibilities, the relevant constraints and the potential signatures could be drastically different.…”

Spontaneous freeze out of dark matter from an early thermal phase transition

“…Refs. [86][87][88]). This possibility would however suppress the interaction between DM and SM fields and be therefore more challenging to detect experimentally.…”

“…(iii) If the energy density of the scalar (either due to its coherent oscillations or to its relic density) comes to dominate the energy density of the universe before the scalar decays into SM particles, the corresponding entropy injection into the visible bath is known to reduce the dark-matter relic abundance [86,87,91]. In that case, this effect has to be taken into account in the numerics.…”

Energy-momentum portal to dark matter and emergent gravity

“…In such scenario, the dark sector is highly secluded from the SM by a feeble coupling or by a very massive mediators 2 which can be a Z 0 [17], moduli fields [18], massive spin-2 particles [19], in the SO (10) framework [20]. Even mediators belonging to the inflaton sector itself [21], or a Kaluza-Klein framework [22,23] and spin- 3 2 particles [24] have been recently analyzed. The case of supergravity is slightly different.…”