Challenges for Inflaton Dark Matter

Abstract

We examine an intriguing possibility that a single field is responsible for both inflation and dark matter, focussing on the minimal set-up where inflation is driven by a scalar coupling to curvature. We study in detail the reheating process in this framework, which amounts mainly to particle production in a quartic potential, and distinguish thermal and non-thermal dark matter options. In the non-thermal case, the reheating is impeded by backreaction and rescattering, making this possibility unrealistic. On the other hand, thermalized dark matter is viable, yet the unitarity bound forces the inflaton mass into a narrow window close to half the Higgs mass.

Dark matter production and reheating via direct inflaton couplings: collective effects

“…In either case, reheating via φ 2 h 2 for a non-thermal inflaton appears unrealistic. Similar arguments apply to the φ 4 inflaton potential [35].…”

“…This could also extend to the full SM or its subset. The energy is then distributed almost democratically among the relativistic degrees of freedom which reach quasi-equilibrium [35],…”

On the Realization of WIMPflation

“…The same interaction which leads to reheating (σφ 2 b 2 ) also brings the inflaton into thermal equilibrium and the inflaton relic density is determined by standard freeze-out conditions. Inflaton dark matter in this respect closely resembles a scalar singlet (Higgs portal) dark matter model [32,36,[65][66][67][68][69][70][71][72][73][74]. To avoid the constraints from direct detection experiments [75][76][77], we must be in one of two mass regimes for m φ : either σ, is relatively large (of order 1) and the inflaton mass is in the range m φ ∼ 1 − 5 TeV (where the upper limit stems from the perturbativity of the couplings) or σ ∼ 10 −4 −4×10 −3 and m φ m h /2 = 62.6 GeV, and the relic density is determined by the resonant annihilation of the inflaton.…”

“…The Higgs decay rate is proportional to its effective mass, Γ h ∼ m eff (t), where m eff (t) √ 2σ|φ(t)|, and for large values of σ the Higgs bosons decay instantly and resonant production does not arise. It was argued in [36] that for k = 4 case, the Higgs bosons decay faster than they are generated through parametric resonance when σ/λ 10 3 . Since resonant dark matter production occurs when σ/λ 3 × 10 7 10 3 , the limit is easily satisfied.…”

“…If, however, the inflaton is protected by a symmetry and hence stable, it may be a candidate for dark matter [27][28][29][30][31][32][33][34][35][36]. Of course, if the inflaton is stable, reheating requires an alternative mechanism, which may be provided perhaps by non-perturbative effects or a coupling to curvature, but generally these are difficult to achieve.…”