In wino veritas? Indirect searches shed light on neutralino dark matter

Abstract

Indirect detection constraints on gamma rays (both continuum and lines) have set strong constraints on wino dark matter. By combining results from Fermi-LAT and HESS, we show that: dark matter made entirely of light nonthermal winos is strongly excluded; dark matter consisting entirely of thermal winos is allowed only if the Milky Way dark matter distribution has a significant (≳ 0.4 kpc) core; and for plausible NFW and Einasto distributions the possibility that winos are all the dark matter can be excluded over the entire range of wino masses from 100 GeV up to 3 TeV. The case of light, nonthermal wino dark matter is particularly interesting in scenarios with decaying moduli that reheat the universe to a low temperature. Typically such models have been discussed for low reheating temperatures, not far above the BBN bound of a few MeV. We show that constraints on the allowed wino relic density push such models to higher reheating temperatures and hence heavier moduli. Even for a flattened halo model consisting of an NFW profile with constant-density core inside 1 kpc and a density near the sun of 0.3 GeV/cm3, for 150 GeV winos current data constrains the reheat temperature to be above 1.4 GeV. As a result, for models in which the wino mass is a loop factor below m 3/2, the data favor moduli that are more than an order of magnitude heavier than m 3/2. We discuss some of the sobering implications of this result for the status of supersymmetry. We also comment on other neutralino dark matter scenarios, in particular the case of mixed bino/higgsino dark matter. We show that in this case, direct and indirect searches are complementary to each other and could potentially cover most of the parameter space.