Significant Gamma Lines from Inert Higgs Dark Matter

TL;DR

It is shown that for this scalar dark matter candidate, the annihilation signal of monochromatic gammagamma and Zgamma final states would be exceptionally strong and ideal to search for with the soon upcoming GLAST satellite.

Abstract

One way to unambiguously confirm the existence of particle dark matter and determine its mass would be to detect its annihilation into monochromatic gamma-rays in upcoming telescopes. One of the most minimal models for dark matter is the inert doublet model, obtained by adding another Higgs doublet with no direct coupling to fermions. For a mass between 40 and 80 GeV, the lightest of the new inert Higgs particles can give the correct cosmic abundance of cold dark matter in agreement with current observations. We show that for this scalar dark matter candidate, the annihilation signal of monochromatic γγand Zγfinal states would be exceptionally strong. The energy range and rates for these gamma-ray line signals make them ideal to search for with the soon upcoming GLAST satellite.

Figures (3)

• Figure 1: The total differential photon distribution from annihilations of an inert Higgs dark matter particle (solid line). Shown separately are the contributions from $H^0 H^0 \rightarrow b \bar{b}$ (dashed line), $\tau^+ \tau^-$ (dash-dotted line) and $Z \gamma$ (dotted line). This is for the benchmark model I in Table \ref{['tab:benchmark']}.
• Figure 2: Predicted gamma-ray spectra from the inert Higgs benchmark models I and II as seen by GLAST (solid lines). The predicted gamma flux is from a $\Delta\Omega=10^{-3}$ sr region around the direction of the galactic center assuming an NFW halo profile (with boost factors as indicated in the figure) and convolved with a 7 % Gaussian energy resolution. The boxes show EGRET data (which set an upper limit for the continuum signal) and the thick line HESS data in the same sky direction. The GLAST sensitivity (dotted line) is here defined as 10 detected events within an effective exposure of 1 m$^2$yr within a relative energy range of $\pm$7 %.
• Figure 3: Annihilation rates into gamma-ray lines $2v\sigma_{\gamma\gamma}$ (upper band) and $v\sigma_{Z\gamma}$ (middle band) from the scan over the IDM parameter space. For comparison the lower-right region indicates the corresponding results within the minimal supersymmetric standard model as obtained with the DarkSUSY package ds.