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.
Highlights
If dark matter is a WIMP with weak-scale interactions with the Standard Model particles, the prospects of discovery at direct detection, indirect detection or collider experiments are good
In many models of WIMP dark matter, if a signal is produced in one experimental channel, a signal will be observed in another
We demonstrate this by considering the extended gamma-ray excess from the galactic centre, observed by the Fermi-LAT satellite
Summary
Owing to the large dark matter number density there, one of the most promising places to look for dark matter annihilation products is a small (∼ 0.1 kpc) region centred on the galactic centre. The following simplified model gives a good fit to the extended gamma-ray excess shown in figure 1. The red shaded region in figure 3 shows the values of the pseudoscalar-dark matter coupling gDM and mass ma that fit the galactic excess at 3σ. In this region we have marginalised over mDM. For mDM = 30 GeV and (ma, gDM) = (40, 0.4), the width is Γa = 1.9 MeV and the largest branching ratio is BR(a → bb) = 89%, followed by ccand τ +τ − at 7% and 4% respectively Once it is kinematically possible for the pseudoscalar to decay into dark matter, this channel dominates.
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