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

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 lose 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 semianalytic model that combines the 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 subgalaxy 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.

Evolution of dark matter microhalos through stellar encounters

“…Mass evolution for microhalos crossing the solar neighborhood as predicted using Eqs. (22) and (14). The random distribution of stars induces variance in the mass evolution; we plot eight example mass trajectories along with the mean and median of 10,000 trajectories (black).…”

Fitting dark matter mass with the radio continuum spectral data of the Ophiuchus cluster

“…However, no observational evidence of these substructures is found. Also, the systematic uncertainty of modelling the substructure contribution is quite large [38] and the effect of the substructure emission near the central region of the Ophiuchus cluster is not very significant. Therefore, we neglect the substructure contributions in our analysis.…”

The galactic center excess from ℤ 3 $$ {\mathbb{Z}}_3 $$ scalar semi-annihilations

“…We note that we could also consider smaller values for the NFW parameters, together with a modest O(10) boost from DM substructure [56,57]. The question of whether, and how large, such an enhancement can be is an active area of current research [58][59][60][61][62]. However, we need a much smaller increase than the O(10 2 -10 3 ) boosts usually considered [61], which is more robust to arguments against the existence of such enhancements.…”