Self-interacting inelastic dark matter: a viable solution to the small scale structure problems

Abstract

Abstract. Self-interacting dark matter has been proposed as a solution to the smallscale structure problems, such as the observed flat cores in dwarf and low surface brightness galaxies. If scattering takes place through light mediators, the scattering cross section relevant to solve these problems may fall into the non-perturbative regime leading to a non-trivial velocity dependence, which allows compatibility with limits stemming from cluster-size objects. However, these models are strongly constrained by different observations, in particular from the requirements that the decay of the light mediator is sufficiently rapid (before Big Bang Nucleosynthesis) and from direct detection. A natural solution to reconcile both requirements are inelastic endothermic interactions, such that scatterings in direct detection experiments are suppressed or even kinematically forbidden if the mass splitting between the two-states is sufficiently large. Using an exact solution when numerically solving the Schrödinger equation, we study such scenarios and find regions in the parameter space of dark matter and mediator masses, and the mass splitting of the states, where the small scale structure problems can be solved, the dark matter has the correct relic abundance and direct detection limits can be evaded.

The distribution of inelastic dark matter in the Sun

“…[50][51][52] for studies of inelastic DM capture by compact stars such as white dwarves and neutron stars. Inelastic DM has also been proposed as a solution to the small scale structure problems in models where a light mediator induces large self-scattering cross sections [53][54][55], and in models where the more massive state is unstable [56][57][58].…”

Displaced lepton jet signatures from self-interacting dark matter bound states

“…2 (right) and smooth the resonance peaks for fixed σ/m χ . In addition, we also expect the favored SIDM region would shift towards lower m Z d values if we include the mass splitting [75,76], but the overall resonant features remain. This is because for given m χ a lighter m Z d is required to compensate the suppression effect caused by the mass splitting.…”

“…Within this limit, the decay length of Z d will be too long to produce DLJ signatures in the LHC detectors. To avoid the direct detection constraints, we assume that the SIDM fermions carry a small Majorana mass that breaks the dark symmetry U(1) d [74][75][76]. Figure 2.…”

“…In the presence of the mass splitting, dark matter self-scattering between the two light states is attractive [75,76]. In this case, a detailed calculation of the self-scattering cross section per mass, σ/m χ , is complicated and numerically expensive, which is beyond the scope of this paper.…”

Strong dark matter self-interaction from a stable scalar mediator

“…On the other hand, in the model with a scalar mediator, even though the DM indirect detection constraints can be avoided since the fermionic DM annihilation is p-wave dominated [54], the DM direct detection upper bounds [55] imply the longevity of the scalar mediator, which would modify the primordial abundances of light elements during Big-Bang nucleosynthesis (BBN) [56][57][58]. Though, there have already been many possible solutions proposed to avoid such tensions for models with scalar and vector mediators [54,[59][60][61][62][63][64][65][66][67][68][69].…”