Split fermionic WIMPs evade direct detection

TL;DR

This paper presents a model with two fermionic WIMPs where the heavy partner acts as a mediator, allowing the light WIMP to evade direct detection constraints while satisfying relic density and indirect detection limits.

Contribution

It introduces a two-WIMP model with a heavy partner that facilitates evasion of direct detection bounds, extending minimal fermionic DM models.

Findings

Viable parameter space exists that evades XENON1t and LUX constraints.

The model satisfies relic density constraints from WMAP/Planck.

Fermi-LAT limits further restrict the parameter space.

Abstract

We consider a model with two gauge singlet fermionic WIMPs communicating with the SM particles by a singlet scalar mediator via a Higgs portal. While the light WIMP is stable and plays the role of the dark matter (DM) candidate, the heavy partner is a short-lived WIMP without contribution to the current DM relic density. Along with the coannihilation effects the heavy WIMP, acting as a mediator in $t$- and $u$-channel DM annihilation cross sections, has a significant effect in finding the viable parameter space against the direct detection constraints provided by XENON1t and LUX experiments. This is an extension to the minimal singlet fermionic DM model whose entire parameter space (except a resonance region) excluded by the latest direct detection experiments. It is found out that there are viable regions in the parameter space which evade direct detection upper bounds and respect the observed DM relic density by WMAP/Planck. We also found that the Fermi-LAT upper limits on the DM annihilation cross section into $b\bar b$ can exclude small regions of the viable parameter space which elude direct detection experiments. This model exemplifies a case within the WIMP paradigm whose DM candidate can escape direct detection experiments nontrivially. Such models are interesting to be studied in collider experiments like the LHC.