Boosting the annihilation boost: Tidal effects on dark matter subhalos and consistent luminosity modeling

TL;DR

This paper develops a semi-analytic model to quantify how tidal stripping affects dark matter subhalo luminosities, revealing a 2-5 times increase in the annihilation boost factor, which impacts gamma-ray dark matter searches.

Contribution

It introduces a new model that accounts for tidal effects on subhalo density profiles, improving the accuracy of boost factor estimates in dark matter annihilation signals.

Findings

Boost factor increases by 2-5 times with tidal effects.

Results are consistent across various host halo masses.

Model is independent of subhalo mass function or concentration-mass relation.

Abstract

In the cold dark matter paradigm, structures form hierarchically, implying that large structures contain smaller substructures. These subhalos will enhance signatures of dark matter annihilation such as gamma rays. In the literature, typical estimates of this boost factor assume a concentration-mass relation for field halos, to calculate the luminosity of subhalos. However, since subhalos accreted in the gravitational potential of their host loose mass through tidal stripping and dynamical friction, they have a quite characteristic density profile, different from that of the field halos of the same mass. In this work, we quantify the effect of tidal stripping on the boost factor, by developing a semi-analytic model that combines mass-accretion history of both the host and subhalos as well as subhalo accretion rates. We find that when subhalo luminosities are treated consistently, the boost factor increases by a factor 2-5, compared to the typical calculation assuming a field-halo concentration. This holds for host halos ranging from sub-galaxy to cluster masses and is independent of the subhalo mass function or specific concentration-mass relation. The results are particularly relevant for indirect dark matter searches in the extragalactic gamma-ray sky.