Coscattering in next-to-minimal dark matter and split supersymmetry

Abstract

In some models of thermal relic dark matter, the relic abundance may be set by inelastic scattering processes (rather than annihilations) becoming inefficient as the universe cools down. This effect has been called coscattering. We present a procedure to numerically solve the full momentum-dependent Boltzmann equations in coscattering, which allows for a precise calculation of the dark matter relic density including the effects of early kinetic decoupling. We apply our method to a simple model, containing a fermionic SU(2) triplet and a fermionic singlet with electroweak-scale masses, at small triplet-singlet mixing. The relic density can be set by either coannihilation or, at values of the mixing angle θ 10 −5 , by coscattering. We identify the parameter ranges which give rise to the observed relic abundance. As a special case, we study bino-like dark matter in split supersymmetry at large µ.

Dark matter relic abundance beyond kinetic equilibrium

“…In fact, it has repeatedly been pointed out that chemical and kinetic decoupling can be intertwined in a way that significantly affects the result of relic density calculations [24][25][26][27][28][29][30][31][32][71][72][73][74][75]. To provide context, we have therefore devoted a large part of this article (Sect.…”

“…A possible solution that has received increased attention is to derive coupled equations for the number density and higher moments of the DM phase-space distribution, making use of the Boltzmann hierarchy [24][25][26][27][28][29]. More recently, there have also been attempts to solve the full Boltzmann equation directly at the phase-space level [30][31][32].…”

Co-scattering in micrOMEGAs: a case study for the singlet-triplet dark matter model

“…In particular, weaker couplings of the DM (χ) to SM particles can lead to a value for the DM relic density that is consistent with the one extracted from measurements of the cosmic microwave background [6]. This can occur in models where the dark sector 1 contains several new particles and co-annihilation processes involving heavier states of the equilibrium in the early Universe will impact the relic density calculation [34], see also [10,30,35]. This can lead to a sizeable systematic uncertainty on the computed Ωh 2 .…”

“…This model extends the SM by two electroweak multiplets: a fermionic singlet χ and a fermionic SU(2) L triplet ψ, which are both odd under a new Z 2 symmetry, while the SM particles are even. Following the notation of [30], but with four-component Majorana spinors, the most general Lagrangian for this model is…”

Co-scattering in micrOMEGAs: A case study for the singlet-triplet dark matter model

“…[23][24][25][26][27][28][29]. The same framework was also used to discuss the usage of the full momentumdependent Boltzmann equations for co-scattering processes in [30]. On the collider side, the model can lead to signatures of long-lived particles, which are heavily searched for at the LHC [31].…”