Gamma rays from the annihilation of singlet scalar dark matter

TL;DR

The paper analyzes a Higgs-portal real scalar singlet as dark matter, deriving a gamma-ray flux from DM annihilation and updating the viable parameter space under relic density and direct-detection constraints. By enforcing $\Omega_S h^2 = 0.11$, the model effectively reduces to two parameters, $m_S$ and $m_h$, with $\lambda$ fixed along each line; direct detection excludes $m_S < 50$ GeV. The gamma-ray flux is computed for Galactic-center/halo scenarios using a NFW profile and $J$-factors, revealing detectable signals for a large portion of the viable space with Fermi-GLAST, depending on background modeling. Overall, the work provides a tightly constrained, testable DM scenario with concrete indirect-detection predictions useful for experiments and model discrimination.

Abstract

We consider an extension of the Standard Model by a singlet scalar that accounts for the dark matter of the Universe. Within this model we compute the expected gamma ray flux from the annihilation of dark matter particles in a consistent way. To do so, an updated analysis of the parameter space of the model is first presented. By enforcing the relic density constraint from the very beginning, the viable parameter space gets reduced to just two variables: the singlet mass and the higgs mass. Current direct detection constraints are then found to require a singlet mass larger than 50 GeV. Finally, we compute the gamma ray flux and annihilation cross section and show that a large fraction of the viable parameter space lies within the sensitivity of Fermi-GLAST.

Figures (5)

• Figure 1: The dark matter density as a function of $m_S$ for $\lambda=0.1$ and different values of the higgs mass.
• Figure 2: The viable parameter space of the scalar singlet model. Along the lines the dark matter constrained is satisfied. We use $m_h=120,150,180, 200$ GeV as reference values for the higgs mass. The grey area surrounding the line corresponding to $m_h=120$ GeV shows the region compatible with the observed dark matter density at $2\sigma$.
• Figure 3: The spin-independent proton-singlet cross section as a function of $m_S$ for different values of the higgs mass. The thin lines show the present constraint from XENON10 and CDMS. The dotted line corresponds to the expected sensitivity of SuperCDMS. Along the lines $\Omega_S h^2=0.11$.
• Figure 4: The integrated photon flux above $1$ GeV as a function of the singlet scalar mass. The predicted gamma flux is from a $\Delta\Omega=10^{-3}$ sr region around the galactic center for a NFW profile.
• Figure 5: The total annihilation cross section at low velocities as a function of $m_S$ for different values of $m_h$. The dashed (dotted) line shows the $\langle\sigma v\rangle$ required to observe a DM annihilation signal at $3\sigma$ significance with one year of Fermi-GLAST data considering the conventional (optimized) diffuse model as background --see figure 9 in Baltz:2008wd.