Light Dark Matter from Entropy Dilution

We investigate a dark sector containing a pair of light non-degenerate scalar particles, with masses in the MeV-GeV range, coupled to the visibile sector through heavier mediators. The heaviest dark state is long-lived, and its decays offer new testable signals. We analyze the prospects for detection with the proposed beam-dump facility SHiP, and the proposed LHC experiments FASER and MATHUSLA. Moreover, we consider bounds from the beam-dump experiment CHARM and from colliders (LEP, LHC and BaBar). We present our results both in terms of an effective field theory, where the heavy mediators have been integrated out, and of a simplified model containing a vector boson mediator, which can be heavy ≳ $$ \mathcal{O}(1) $$ O 1 TeV, or light $$ \mathcal{O}(10) $$ O 10 GeV. We show that future experiments can test large portions of the parameter space currently unexplored, and that they are complementary to future High-Luminosity LHC searches.

Section: Jhep03(2021)272mentioning

confidence: 69%

Probing light dark scalars with future experiments

Bertuzzo

Taoso

2021

“…This effect of reheating and decreasing direct detection signatures compared to the predictions of standard cosmology applies generally to any DM candidate -see e.g. [139][140][141][142][143]. In THPDM, σv ∝ σ SN ∝ λ 2 eff .…”

Section: Jhep08(2021)009mentioning

confidence: 76%

Twin Higgs portal dark matter

Curtin

Gryba

2021

Many minimal models of dark matter (DM) or canonical solutions to the hierarchy problem are either excluded or severely constrained by LHC and direct detection null results. In particular, Higgs Portal Dark Matter (HPDM) features a scalar coupling to the Higgs via a quartic interaction, and obtaining the measured relic density via thermal freeze-out gives definite direct detection predictions which are now almost entirely excluded. The Twin Higgs solves the little hierarchy problem without coloured top partners by introducing a twin sector related to the Standard Model (SM) by a discrete symmetry. We generalize HPDM to arbitrary Twin Higgs models and introduce Twin Higgs Portal Dark Matter (THPDM), which features a DM candidate with an SU(4)-invariant quartic coupling to the Twin Higgs scalar sector. Given the size of quadratic corrections to the DM mass, its most motivated scale is near the mass of the radial mode. In that case, DM annihilation proceeds with the full Twin Higgs portal coupling, while direct detection is suppressed by the pNGB nature of the 125 GeV Higgs. For a standard cosmological history, this results in a predicted direct detection signal for THPDM that is orders of magnitude below that of HPDM with very little dependence on the precise details of the twin sector, evading current bounds but predicting possible signals at next generation experiments. In many Twin Higgs models, twin radiation contributions to ∆Neff are suppressed by an asymmetric reheating mechanism. We study this by extending the νMTH and X MTH models to include THPDM and compute the viable parameter space according to the latest CMB bounds. The injected entropy dilutes the DM abundance as well, resulting in additional suppression of direct detection below the neutrino floor.

“…[8] for k → 2 reactions taking place within the dark sector. We then go on to consider the possibility of a modification to the thermal history of the Universe, taking up the frequently occuring scenario of an intermediate period of matter domination in the pre-big bang nucleosynthesis (BBN) era [18][19][20][21][22][23][24][25][26]. It is observed in section 5 that though the unitarity limits are weaker in such scenarios primarily due to the dilution of DM density from late-time entropy production, there are strong JHEP03(2021)133 implications of unitarity to the possible values of the reheating temperature at which the radiation dominated Universe is restored.…”

Section: Introductionmentioning

confidence: 99%

Unitarity limits on thermal dark matter in (non-)standard cosmologies

Bhatia

Mukhopadhyay

2021

Using the upper bound on the inelastic reaction cross-section implied by S-matrix unitarity, we derive the thermally averaged maximum dark matter (DM) annihilation rate for general k → 2 number-changing reactions, with k ≥ 2, taking place either entirely within the dark sector, or involving standard model fields. This translates to a maximum mass of the particle saturating the observed DM abundance, which, for dominantly s-wave annihilations, is obtained to be around 130 TeV, 1 GeV, 7 MeV and 110 keV, for k = 2, 3, 4 and 5, respectively, in a radiation dominated Universe, for a real or complex scalar DM stabilized by a minimal symmetry. For modified thermal histories in the pre-big bang nucleosynthesis era, with an intermediate period of matter domination, values of reheating temperature higher than $$ \mathcal{O}(200) $$ O 200 GeV for k ≥ 4, $$ \mathcal{O}(1) $$ O 1 TeV for k = 3 and $$ \mathcal{O}(50) $$ O 50 TeV for k = 2 are strongly disfavoured by the combined requirements of unitarity and DM relic abundance, for DM freeze-out before reheating.