Confronting Galactic center and dwarf spheroidal gamma-ray observations with cascade annihilation models

Abstract

Many particle dark matter models predict that the dark matter undergoes cascade annihilations, i.e. the annihilation products are 4-body final states. In the context of model-independent cascade annihilation models, we study the compatibility of the dark matter interpretation of the Fermi-LAT Galactic center gamma-ray emission with null detections from dwarf spheroidal galaxies. For canonical values of the Milky Way density profile and the local dark matter density, we find that the dark matter interpretation to the Galactic center emission is strongly constrained. However, uncertainties in the dark matter distribution weaken the constraints and leave open dark matter interpretations over a wide range of mass scales.

Prospects for indirect detection of frozen-in dark matter

“…We showed that feebly-coupled, frozen-in DM -which was never in thermal equilibrium with the SM particles and is thus of non-thermal origin -can result in observ- [35] is shown by the purple ellipse, and the upper limit for the cross section from FERMI dwarf observations is shown by the purple dashed line. The blue shaded regions show where the decay channel s → τ τ is not the dominant decay mode, and therefore can not be used to fit the excess.…”

“…The first inequality is needed to allow the AA → ss annihilation process, while the second inequality follows from the requirement that the DM particles A reach chemical equilibrium in the hidden sector after the freeze-in production. Therefore, the region that best fits the excess assuming the 4b final state, with m A 50 GeV [35] lies mostly outside our allowed parameter space. However, as discussed in [35], the excess may almost as well be fitted with a 4τ final state, which is the dominant final state in our scenario assuming 2m τ ≤ m s < 2m b .…”

“…Therefore, the region that best fits the excess assuming the 4b final state, with m A 50 GeV [35] lies mostly outside our allowed parameter space. However, as discussed in [35], the excess may almost as well be fitted with a 4τ final state, which is the dominant final state in our scenario assuming 2m τ ≤ m s < 2m b .…”

“…The case of a four-body final state resulting from a cascade annihilation, such as in our U (1) scenario, was analyzed in [35,36]. Since we are considering the production of DM originating from Higgs decays, we will constrain our analysis to the mass hierarchy m s ≤ m A m h /2.…”

Dark matter in dwarf spheroidal galaxies and indirect detection: a review

“…Dwarf spheroidals provide an ideal independent cross check on a dark matter interpretation of the emission from the inner Galaxy. Indeed at present the lack of excess gamma-ray signal from dSphs imposes constraints on annihilation cross-section, and also strongly constrains interpretations for a variety of different annihilation channels [100]. Future improvements in the gamma-ray limits from dSphs, and also possibly the discovery of new dSphs, are expected to go a way towards confirming or ruling out the dark matter interpretation of the gamma-rays from the inner Galaxy [133].…”