Abstract
The density spike of dark matter (DM) in the subparsec region near the supermassive black hole at the Galactic Center can provide potentially observable gamma-ray signals coming from DM annihilations. Taking Fermi-$LAT$ data for the gamma-ray flux from the point source 3FGL J1745.6-2859c (Sgr A*), we calculate the resulting constraints on generic models of DM, allowing for the possibility of a non-negligible velocity-dependent component of the annihilation cross section. We consider a variety of selections for the astrophysical parameters that describe the spike profile and find that the gamma-ray flux is strongly dependent on these selections, particularly the modelling of spike depletion effects due to gravitational interactions with baryons, which affect the spike radius and steepness profile. We calculate constraints on the DM parameter space for both attenuated and idealized spikes, considering different choices for the steepness profiles in each case. We find that for the most conservative selection of parameters, corresponding to a depleted spike with an NFW cusp profile, the gamma-ray flux for a 100 GeV thermal relic is lower than current observational constraints by several orders of magnitude. For more optimistic choices of parameters corresponding to spikes that have not been attenuated, bounds on DM masses can be obtained for a variety of choices of steepness profiles. We then specialize to a class of simplified models of fermionic DM that annihilate dominantly through the $t-$channel exchange of two scalar mediators with arbitrary mixing angle $\alpha$, and calculate the indirect detection constraints coming from the DM spike. Along the way, we discuss constraints on the astrophysical parameters describing the DM spike, taking the Galactic Center excess as a signal of DM annihilation.
Highlights
The particle nature of dark matter (DM) is an area of intense investigation which has the potential to shed light on fundamental questions about the standard model (SM), especially the hierarchy problem
We present a particular example that demonstrates the impact of the dark matter profile, including a spike, on conclusions regarding the particle physics of DM interactions
We have explored the impacts of the modeling of the dark matter distribution in our Galaxy, including a potential dark matter spike at the Galactic center, on indirect signals of dark matter annihilation
Summary
The particle nature of dark matter (DM) is an area of intense investigation which has the potential to shed light on fundamental questions about the standard model (SM), especially the hierarchy problem. For DM candidates with weak-scale couplings and mass, a calculation of the relic density automatically yields a value that is close to the measured dark matter abundance. This striking fact, a success of the so-called weakly interacting massive particle (WIMP) paradigm, reinforces the possibility that DM is deeply connected to new physics at the weak scale.
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