Extended gamma-ray emission from Coy Dark Matter

TL;DR

Coy Dark Matter shows that a WIMP can produce a large indirect signal without coincident signals in direct detection or colliders. A Dirac DM $\chi$ coupled to a light pseudoscalar mediator $a$ with Yukawa-like couplings can fit the Fermi-LAT extended Galactic Center gamma-ray excess with $m_{\rm DM} \sim 20$–$50$ GeV and $\langle \sigma v\rangle \sim 3\times10^{-26}$ cm$^3$ s$^{-1}$, predominantly via $\chi\bar{\chi}\to b\bar{b}$. Collider constraints are weak in the favored region, though a future 14 TeV monojet search could probe $m_a \gtrsim 2 m_{\rm DM}$; direct detection and other indirect searches generally do not constrain the model due to momentum suppression and channel choices. The results emphasize that the Galactic Center gamma-ray excess could be the sole experimental hint of DM, highlighting the importance of considering astrophysical alternatives and complementary searches.

Abstract

We show that it is possible for WIMP dark matter to produce a large signal in indirect dark matter searches without producing signals elsewhere. We illustrate our point by fitting the Fermi-LAT extended galactic gamma-ray excess with a simple model of Dirac dark matter that annihilates primarily into b quarks via a pseudoscalar. Current collider constraints are weak while the 14 TeV LHC run will constrain a limited portion of the parameter space. No signal is expected in additional indirect searches or at future direct detection experiments. Our results emphasise the importance of fully understanding potential indirect signals of dark matter as they may provide the only information about the dark matter particle.

Figures (3)

• Figure 1: The data points show the extended gamma-ray excess from a $7\degree\times7\degree$ region centred on the galactic centre (from Gordon:2013vta). The red and black error bars show the systematic and statistical uncertainties respectively. The blue solid line shows the photon spectrum corresponding to 30 GeV dark matter with an annihilation cross-section that gives the observed relic density. The branching ratios are determined by the Yukawa couplings $y_f$.
• Figure 2: The solid, dashed and dotted contours show the 1, 2 and 3$\sigma$ favoured regions in the $m_{\rm{DM}}$-$\langle\sigma v\rangle$ plane, along with the best fit point, shown by the dot. The branching ratios are determined by the Yukawa couplings $y_f$. The excess is consistent with an annihilation cross-section that gives the observed dark matter relic density.
• Figure 3: The red shaded region shows the values of $g_{\rm{DM}}$ and $m_a$ that fit the galactic excess at $3\sigma$ (marginalising over $m_{\rm{DM}}$). The red dashed line shows the values of $g_{\rm{DM}}$ and $m_a$ that give $\langle \sigma v \rangle=3\times10^{-26}~\text{cm}^3\,\text{s}^{-1}$ for $m_{\rm{DM}}=30$ GeV. The solid blue line shows the constraint from the current 8 TeV CMS monojet search, and the blue dashed line our extrapolation of a similar search at 14 TeV with $40~\hbox{fb}^{-1}$.