Implications of a 130 GeV gamma-ray line for dark matter

Abstract

Recent reports of a gamma-ray line feature at $\ensuremath{\sim}130\text{ }\text{ }\mathrm{GeV}$ in data from the Fermi Gamma-Ray Space Telescope have generated a great deal of interest in models in which dark matter particles annihilate with a sizable cross section to final states including photons. In this paper, we take a model-independent approach and discuss a number of possibilities for dark matter candidates which could potentially generate such a feature. While we identify several scenarios which could lead to such a gamma-ray line, these models are each fairly constrained. In particular, viable models require large couplings ($g\ensuremath{\gtrsim}1--3$) and additional charged particles with masses in the range of approximately $\ensuremath{\sim}130--200\text{ }\text{ }\mathrm{GeV}$. Furthermore, lower energy gamma-ray constraints from the Galactic center force us to consider scenarios in which the dark matter annihilates in the early Universe through velocity-suppressed processes or to final states which yield relatively few gamma-rays (such as ${e}^{+}{e}^{\ensuremath{-}}$, ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, or $\ensuremath{\nu}\overline{\ensuremath{\nu}}$). An exception to these conclusions can be found in models in which the dark matter annihilates to heavy intermediate states which decay to photons to generate a linelike gamma-ray spectrum.