In Wino Veritas? Indirect Searches Shed Light on Neutralino Dark Matter

TL;DR

This paper uses gamma-ray data from Fermi-LAT and HESS to constrain wino dark matter models, showing that most scenarios are excluded unless the Milky Way's dark matter distribution has a significant core, with implications for supersymmetry.

Contribution

It provides new constraints on wino dark matter and related supersymmetric models by combining gamma-ray observations with dark matter distribution assumptions.

Findings

Light nonthermal wino dark matter is strongly excluded.

Thermal wino dark matter is only allowed with a significant galactic core.

Reheat temperature constraints imply heavier moduli and impact supersymmetry models.

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: light nonthermal wino dark matter is strongly excluded; thermal wino dark matter 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 entire range of wino masses from 100 GeV up to 3 TeV can be excluded. 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/cm^3, 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 the gravitino mass, the data favor moduli that are more than an order of magnitude heavier than the gravitino. 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.