Sommerfeld-Enhanced Annihilation in Dark Matter Substructure: Consequences for Constraints on Cosmic-Ray Excesses

TL;DR

This paper explores how small, dense dark matter subhalos significantly impact the expected signals from Sommerfeld-enhanced annihilation, altering constraints from cosmic-ray and gamma-ray observations.

Contribution

It demonstrates that local substructure can change the parameter space for dark matter models explaining cosmic-ray excesses, weakening existing observational constraints.

Findings

Substructure enhances local annihilation signals in dark matter models.

Constraints from the inner galaxy and CMB are less restrictive with substructure.

Certain mediator masses (~1-200 MeV) become viable due to substructure effects.

Abstract

In models of dark matter (DM) with Sommerfeld-enhanced annihilation, where the annihilation rate scales as the inverse velocity, N-body simulations of DM structure formation suggest that the local annihilation signal may be dominated by small, dense, cold subhalos. This contrasts with the usual assumption of a signal originating from the smooth DM halo, with much higher velocity dispersion. Accounting for local substructure modifies the parameter space for which Sommerfeld-enhanced annihilating DM can explain the PAMELA and Fermi excesses. Limits from the inner galaxy and the cosmic microwave background are weakened, without introducing new tension with substructure-dependent limits, such as from dwarf galaxies or isotropic gamma-ray studies. With substructure, previously excluded parameter regions with mediators of mass ~1-200 MeV are now easily allowed. For O(MeV) mediators, subhalos in a specific range of host halo masses may be evaporated, further suppressing diffuse signals without affecting substructure in the Milky Way.