Prompt cusps and the dark matter annihilation signal

Abstract

As the first dark matter objects gravitationally condense, a density cusp forms immediately at every initial density maximum. Numerical simulations and theoretical arguments suggest that these prompt cusps can survive until the present day. We show that if dark matter is a thermally produced weakly interacting massive particle, many thousands of prompt cusps with individual masses similar to that of the Earth may be present in every solar mass of dark matter. This radically alters predictions for the amount and spatial distribution of dark matter annihilation radiation. The annihilation rate is boosted by at least an order of magnitude compared to previous predictions, both in the cosmological average and within galaxy-scale halos. Moreover, the signal is predominantly boosted outside of the centers of galactic halos, so alternative targets become significantly more attractive for indirect-detection searches. For example, prompt cusps present new opportunities to test the dark matter interpretation of the Galactic Center γ-ray excess by searching for similar spectral signatures in the isotropic γ-ray background and large-scale cosmic structure.

Cosmology of axion dark matter

“…The QCD axion lives along a single line in this parameter space defined by Eq. (52). In reference to the discussion in earlier sections, I have put the "predicted" range for the QCD axion mass when…”

“…Unfortunately, the physical size of the core is inversely proportional to the dark matter mass, so there is a conflict between the core-cusp issue wanting for a light mass to explain the sizes of cores, while the Lyman-𝛼 forest tightly constraining the axion mass to be above 10 −21 eV in order to not underproduce small-scale structure [430]. 52 Nonetheless, the phenomenology of the fuzzy dark matter scenario remains intriguing, and there are several other implications of the system that, if they can be understood properly, will allow much more precise tests of the model. For instance, one such phenomenon is the existence of fluctuating "quasiparticles" due to wave interference as seen in Fig.…”

“…6See also Refs [51][52][53][54][55][56]. for more recent work on understanding the small-scale limits of CDM halos.…”

Collisionless Relaxation from Near-equilibrium Configurations: Linear Theory and Application to Tidal Stripping

“…In this section, we apply the matrix method to model the tidal evolution of the central density cusp of cold DM subhalos. The detailed properties of the central density profile of DM subhalos are of particular relevance for the study of potential signals of DM self-annihilation and decay, which scale with ρ 2 (r) and ρ(r), respectively (see, e.g., Stref et al 2019;Facchinetti et al 2022;Stücker et al 2023b;Delos & White 2023;Lovell 2024). Models of the expected signals need to take into account the evolution of subhalo DM density profiles in the tidal field of the Milky Way.…”

“…As an example, we apply our method to study the response of Hernquist (1990) spheres with initially isotropic kinematics to energy-based mass removal (similar to the initial conditions studied in Drakos et al 2020, Amorisco 2021, Errani et al 2022, and Stücker et al 2023a, approximating the type of perturbation typical for weak tidal encounters of cold DM subhalos. A theoretical understanding of the detailed phasespace structure of tidally stripped subhalos is of relevance, for example, for the modeling of Milky Way dwarf galaxies (see, e.g., Peñarrubia et al 2008Peñarrubia et al , 2010, the search for dark substructures through strong gravitational lensing (e.g., Vegetti & Koopmans 2009;Vegetti et al 2010;Despali et al 2022), as well as the modeling of potential DM annihilation or decay signals (e.g., Goerdt et al 2007;Stref et al 2019;Facchinetti et al 2022;Stücker et al 2023b;Delos & White 2023;Lovell 2024).…”