Signatures of non-thermal dark matter with kination and early matter domination. Gravitational waves versus laboratory searches

Abstract

The non-thermal production of dark matter (DM) usually requires very tiny couplings of the dark sector with the visible sector and therefore is notoriously challenging to hunt in laboratory experiments. Here we propose a novel pathway to test such a production in the context of a non-standard cosmological history, using both gravitational wave (GW) and laboratory searches. We investigate the formation of DM from the decay of a scalar field that we dub as the reheaton, as it also reheats the Universe when it decays. We consider the possibility that the Universe undergoes a phase with kination-like stiff equation-of-state (wkin> 1/3) before the reheaton dominates the energy density of the Universe and eventually decays into Standard Model and DM particles. We then study how first-order tensor perturbations generated during inflation, the amplitude of which may get amplified during the kination era and lead to detectable GW signals. Demanding that the reheaton produces the observed DM relic density, we show that the reheaton’s lifetime and branching fractions are dictated by the cosmological scenario. In particular, we show that it is long-lived and can be searched by various experiments such as DUNE, FASER, FASER-II, MATHUSLA, SHiP, etc. We also identify the parameter space which leads to complementary observables for GW detectors such as LISA and u-DECIGO. In particular we find that a kination-like period with an equation-of-state parameter wkin ≈ 0.5 and a reheaton mass $$ \mathcal{O} $$ O (0.5–5) GeV and a DM mass of $$ \mathcal{O} $$ O (10–100) keV may lead to sizeable imprints in both kinds of searches.

Gravitational wave from graviton Bremsstrahlung during reheating

“…In computing the 3-body decay widths, we follow two complementary approaches: a) we explicitly construct the graviton polarization tensors, and b) we utilize the polarization sum and show that our expressions converge in either case, however, differing from previous analyses reported in refs. [17,18,22]. It is then possible to compute the GW energy density from the differential 3-body decay width of the inflaton.…”

Cosmological imprints of SUSY breaking in models of sgoldstinoless non-oscillatory inflation

“…It was demonstrated for example in refs. [55,76] that the spectrum of gravitational waves produced during inflation may lead to observable signals for gravitational wave detectors when the Universe undergoes a long phase of kination after inflation. Moreover, it is known that the production of primordial black holes usually goes with a secondary spectrum of gravitational waves coming from the next-to-leading order terms in perturbation theory [77][78][79].…”

Measuring inflaton couplings via primordial gravitational waves

“…It is, however, well established that the presence of non-standard cosmologies, e.g., an early stiff era before radiation domination, breaks such a scale invariance. In this case, the GW spectrum becomes significantly blue-tilted in the frequency range corresponding to the modes crossing the horizon during the stiff period [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. 1 In addition, the amplitude of the tensor power spectrum becomes considerably enhanced, as compared to the standard scenario, where the Universe immediately transitioned from the inflationary into radiation-dominated phase.…”