Freeze-In dark matter with displaced signatures at colliders

Abstract

Dark matter, X, may be generated by new physics at the TeV scale during an early matterdominated (MD) era that ends at temperature T R TeV. Compared to the conventional radiation-dominated (RD) results, yields from both Freeze-Out and Freeze-In processes are greatly suppressed by dilution from entropy production, making Freeze-Out less plausible while allowing successful Freeze-In with a much larger coupling strength. Freeze-In is typically dominated by the decay of a particle B of the thermal bath, B → X. For a large fraction of the relevant cosmological parameter space, the decay rate required to produce the observed dark matter abundance leads to displaced signals at LHC and future colliders, for any m X in the range keV < m X < m B and for values of m B accessible to these colliders. This result applies whether the early MD era arises after conventional inflation, when T R is the usual reheat temperature, or is a generic MD era with an alternative origin. In the former case, if m X is sufficiently large to be measured from kinematics, the reheat temperature T R can be extracted. Our result is independent of the particular particle physics implementation of B → X, and can occur via any operator of dimension less than 8 (4) for a post-inflation (general MD) cosmology. An interesting example is provided by DFS axion theories with TeV-scale supersymmetry and axino dark matter of mass GeV to TeV, which is typically overproduced in a conventional RD cosmology. If B is the higgsino, h, Higgs, W and Z particles appear at the displaced decays,h → hã, Zã andh ± → W ±ã . The scale of axion physics, f , is predicted to be in the range (3 × 10 8 − 10 12 ) GeV and, over much of this range, can be extracted from the decay length.

Observational constraints on decoupled hidden sectors

“…Hence, the dark matter particle mass is bounded from above by the isocurvature bound (21) and from below by (22),…”

“…We investigate in detail the interplay between the constraints arising from the cosmological and astrophysical observations. Earlier studies on observational properties of frozen-in dark matter in similar models include the case of an ultra-strongly interacting dark matter [16], cosmological, astrophysical and collider constraints on sterile neutrinos [17][18][19][20], and displaced signatures at colliders [21,22]. Frozen-in dark matter has also been used to explain the disagreement between structure formation in cold dark matter simulations and observations [23].…”

Saxion cosmology for thermalized gravitino dark matter

“…[23], while for relic particles produced at some temperature T between T NA and T Rs the dilution factor is less:…”

“…From T Rs up to some temperature T NA this MD era is non-adiabatic (MD NA ): the radiation density is dominated by the products of recently decayed saxions rather than from pre-existing red-shifted radiation, giving T ∝ 1/a 3/8 in ref. [23]. On the other hand at temperatures above T NA there are so few saxion decays that the MD era is adiabatic (MD A ), with T ∝ 1/a.…”

“…where Cχ 0H is the higgsino component of the neutralino LOSP [23]. This is applicable to all panels of figure 4, except the upper left since we need µ > mã.…”