The universe resembles a giant sponge: bright filaments of galaxies weave around enormous dark voids. Inside these filaments and walls hide clumps of invisible dark matter — halos. When dark matter particles collide and decay, they produce ordinary particles that telescopes can catch. But the strength of this signal depends not only on the size of the halo.
Dark matter is not spread uniformly; it clumps together like flour in dough. Small clumps within a large halo amplify the decay signal — an effect known as the boost. Previously, it was thought that the boost is the same for all halos of a given mass, regardless of their location. New research shows that the cosmic environment changes the rules of the game. Halos in filaments, walls, and voids have different concentrations and different numbers of small sub-clumps.
The scientists used simulations to calculate how the environment affects the boost. It turns out that in filaments, for light halos the signal is 15% weaker than average, while for heavy halos it is 12% stronger. In voids, the signal is always suppressed by about a third. This is similar to how the volume of a choir depends on the acoustics of the hall: the same choir sounds different in a cathedral than in an empty room.
Knowing how the environment alters the boost will help predict more precisely where to look for dark matter signals. It will also aid in modeling gravitational lenses — when massive halos bend the light of distant galaxies like eyeglass lenses. The cosmic web turns out to be not just a pretty picture but a crucial factor in the hunt for the invisible.
as written by the authors arXiv:2604.26072
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.
The cosmic web is the largest structure in the universe: its filaments stretch for hundreds of millions of light-years, and the voids between them are comparable to the distance from Earth to neighboring galaxy clusters.