Abstract
If dark matter inhabits an expanded ``hidden sector'', annihilations may proceed through sequential decays or multi-body final states. We map out the potential signals and current constraints on such a framework in indirect searches, using a model-independent setup based on multi-step hierarchical cascade decays. While remaining agnostic to the details of the hidden sector model, our framework captures the generic broadening of the spectrum of secondary particles (photons, neutrinos, e+e− and p̄ p) relative to the case of direct annihilation to Standard Model particles. We explore how indirect constraints on dark matter annihilation limit the parameter space for such cascade/multi-particle decays. We investigate limits from the cosmic microwave background by Planck, the Fermi measurement of photons from the dwarf galaxies, and positron data from AMS-02. The presence of a hidden sector can change the constraints on the dark matter by up to an order of magnitude in either direction (although the effect can be much smaller). We find that generally the bound from the Fermi dwarfs is most constraining for annihilations to photon-rich final states, while AMS-02 is most constraining for electron and muon final states; however in certain instances the CMB bounds overtake both, due to their approximate independence on the details of the hidden sector cascade. We provide the full set of cascade spectra considered here as publicly available code with examples at http://web.mit.edu/lns/research/CascadeSpectra.html.
Highlights
Indirect searches provide one of the best ways to probe the nature of dark matter (DM) beyond gravitational interactions
At a fixed mass and cross-section, larger numbers of cascade steps will tend to produce a larger number of lower-energy photons; at low masses, some of these photons may lie outside the energy range of the Fermi analysis, and the astrophysical backgrounds will generally be larger at low energies
We have shown that results from current DM indirect searches can be extended to constrain a broad space of dark sector models
Summary
Indirect searches provide one of the best ways to probe the nature of dark matter (DM) beyond gravitational interactions. Many models have been proposed in which DM annihilates directly to a pair of SM particles through, for example, a Higgs [1, 2], gauge boson [3], axion [4], or neutrino [5] Going beyond these simple models, we can consider scenarios in which DM is secluded in its own rich dark sector; such a setup is well motivated from top-down considerations The mediators subsequently decay into SM particles, which in turn decay to stable and detectable photons, neutrinos, electrons, positrons, protons and/or antiprotons We refer to this pattern as a “cascade annihilation” or “cascade”, with a number of steps given by the number of distinct on-shell dark-sector states between the initial DM annihilation and the production of SM particles.
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