Late-Time Dark Matter Oscillations and the Core-Cusp Problem

TL;DR

This paper proposes a novel late-time dark matter annihilation mechanism, driven by oscillations in asymmetric dark matter models, to transform cuspy profiles into cores, offering an alternative solution to the core-cusp problem.

Contribution

It introduces a new scenario where dark matter oscillations trigger annihilation at late times, effectively flattening galactic density profiles.

Findings

Dark matter oscillations can eliminate cusps in galaxy profiles.

Annihilation is more efficient than elastic scattering in certain parameter regions.

The mechanism provides an alternative to self-interacting dark matter for solving the core-cusp problem.

Abstract

The core-cusp problem persists as an unresolved tension between the predictions of $\Lambda$CDM cosmology and observations of dark matter (DM) profiles in dwarf spheroidal and other galaxies. We present a novel scenario for converting cusps into cores through reactivation of DM annihilation in galaxies at late times. This can happen in asymmetric DM models when there is a very small DM-number violating mass term that causes oscillations between DM and its antiparticle. Using analytic methods as well as gravitational N-body simulations, we show that this mechanism can robustly eliminate cusps from galactic DM profiles for light fermionic DM of mass $m_\chi\sim (0.1-1)$ GeV and a lighter mediator into which the DM can annihilate. We identify regions of parameter space where annihilation of DM particles is more efficient than elastic scattering at reducing the inner density of the DM profile. Dark matter annihilation is therefore a qualitatively distinct alternative to the mechanism of elastic self-interacting dark matter for addressing the cusp-core problem.