Caught in the Cosmic Web: Environmental Impacts on the Halo Substructure Boosts to Dark Matter Annihilation Signals

TL;DR

This paper investigates how the large-scale cosmic environment influences dark matter subhalo boosts, revealing environment-dependent variations in annihilation signal predictions across different cosmic web structures.

Contribution

It introduces an environment-dependent framework for predicting dark matter subhalo boosts, extending standard models to include cosmic web influences on halo substructure.

Findings

Filament haloes show a transition from 15% suppression to 12% enhancement with mass.

Void haloes are suppressed by roughly 30-33% across host-mass range.

Environment-aware boost prescriptions can improve indirect detection and lensing models.

Abstract

The annihilation of dark matter (DM) particles is expected to produce Standard Model particles, providing a potential indirect signature of DM. The clumpy substructure of DM haloes amplifies the expected annihilation signal, an effect commonly quantified by the subhalo boost factor. Standard semi-analytic models usually treat this boost as a universal function of host-halo mass, neglecting systematic variations induced by the large-scale environment. In this work, we extend this framework by incorporating the influence of the cosmic web on subhalo populations. Using simulation-calibrated, environment-dependent ratios for host-halo concentrations, the subhalo mass function, and internal-structure proxies of subhalos based on the $V_{\max}$--$R_{\max}$ relation, we compute environment-conditioned boost predictions for haloes residing in filaments, walls, and voids. Our main result is the boost factor at fixed host-halo mass, expressed relative to the cosmic-mean prediction, $B(M,\mathrm{env})/B_{\mathrm{CM}}(M)$. We find a clear environmental modulation: in the fiducial distance-dependent model, filament haloes show a mass-dependent transition from a $\sim 15\%$ suppression at the low-mass end to a modest enhancement of $\sim 12\%$ for massive hosts, wall haloes remain intermediate, while void haloes stay suppressed by roughly $30$--$33\%$ across the explored host-mass range. These results should be interpreted as deterministic model predictions obtained by propagating environment-dependent ingredient ratios through two standard semi-analytic boost frameworks. We provide an environment-aware prescription for subhalo boosts, together with modular environmental corrections that may also be useful in indirect-detection forecasts, strong-lensing mass modeling, and related halo-population applications.