Relic density and PAMELA events in a heavy wino dark matter model with Sommerfeld effect

TL;DR

This paper demonstrates that a 4 TeV wino dark matter model, accounting for Sommerfeld enhancement, can simultaneously explain PAMELA positron data, fit Fermi-LAT gamma-ray observations, and match the observed relic density.

Contribution

It shows that including Sommerfeld enhancement in relic density calculations allows a 4 TeV wino to be a viable dark matter candidate explaining cosmic ray observations.

Findings

Sommerfeld enhancement boosts annihilation cross section to ~10^4 near resonance.

Correct relic density is achieved for 4 TeV wino when enhancement is included.

Model explains PAMELA positron flux and is compatible with Fermi-LAT gamma-ray data.

Abstract

In a wino LSP scenario the annihilation cross section of winos gravitationally bound in galaxies can be boosted by a Sommerfeld enhancement factor which arises due to the ladder of exchanged W bosons between the initial states. The boost factor obtained can be in the range S ~ 10^4 if the mass is close to the resonance value of M ~ 4 TeV. In this paper we show that if one takes into account the Sommerfeld enhancement in the relic abundance calculation then the correct relic density is obtained for 4 TeV wino mass due to the enhanced annihilation after their kinetic decoupling. At the same time the Sommerfeld enhancement in the \chi \chi --> W^+ W^- annihilation channel is sufficient to explain the positron flux seen in PAMELA data without significantly exceeding the observed antiproton signal. We also show that (e^- + e^+) and gamma ray signals are broadly compatible with the Fermi-LAT observations. In conclusion we show that a 4 TeV wino DM can explain the positron and antiproton fluxes observed by PAMELA and at the same time give a thermal relic abundance of CDM consistent with WMAP observations.