Fitting the Galactic Center gamma-ray excess with cascade annihilations

Abstract

The apparent excess of gamma rays in an extended region in the direction of the galactic center has a spatial distribution and amplitude that are suggestive of dark matter annihilations. If this excess is indeed due to dark matter annihilations, it would indicate the presence of both dark matter and an additional particle beyond the Standard Model that mediates the interactions between the dark matter and Standard Model states. We introduce reference models describing dark matter annihilation to pairs of these new mediators, which decouples the SM-mediator coupling from the thermal annihilation cross section and easily explains the lack of direct detection signals. We determine the parameter regions that give good descriptions of the gamma ray excess for several motivated choices of mediator couplings to the SM. We find fermion dark matter with mass 7-26 GeV and a dark vector mediator, or scalar dark matter in the 10-50 GeV range (Higgs portal mediator) or 10-65 GeV range (gluophilic mediator) can provide a comparable or improved fit, compared to the case of direct annihilation. We demonstrate that these models can easily satisfy all constraints from collider experiments, direct detection, and cosmology.

The windows for kinetically mixed Z′-mediated dark matter and the galactic center gamma ray excess

“…We undertake a similar study here for the case where Z couples to the SM through gauge kinetic mixing (this possibility was also considered in [28]). Since the models that give the best fit to the GC excess spectrum have light Z , the couplings of Z to fermions are to a good approximation given by the − c W c ζ eQ i term in (3.5), i.e., the Z couples to their charges.…”

“…On the other hand, refs. [28,29] pointed out that these constraints are alleviated if m Z < m χ so that χχ → Z Z → 4f (where f is a SM fermion) can proceed through on-shell Z bosons in the GC. The coupling of Z to ff can be much smaller in this case, since the on-shell Z need only decay eventually into SM particles.…”

Dark matter interpretation of the Fermi -LAT observation toward the Galactic Center

“…More generalized constructions are employed here, and their parameters are fit together with the IEM parameters as described in Section II. Of course, models with light mediators are also interesting, and worthy of investigation in their own right [46][47][48][49][50][51][52][53]. We leave exploration of such theories for future work.…”

Detecting hidden particles with MATHUSLA

“…A long lifetime for the lightest hidden sector particle due to this feeble connection allows for the new physics to have evaded detection at the LHC and many precision experiments. Hidden sector models are well-motivated and have been used to explain a wide variety of outstanding deficiencies in the standard model, such as naturalness [6,7], dark matter [8][9][10], inflation [11], m ν [12], the proton radius puzzle [13][14][15], and the ðg − 2Þ μ anomaly [16,17]. The light particles of these hidden sectors can potentially be produced in a variety of ways, including rare meson decays and exotic Higgs decays [18].…”