Abstract
A natural possibility for dark matter is that it is composed of the stable pions of a QCD-like hidden sector. Existing literature largely assumes that pion self-interactions alone control the early universe cosmology. We point out that processes involving vector mesons typically dominate the physics of dark matter freeze-out and significantly widen the viable mass range for these models. The vector mesons also give rise to striking signals at accelerators. For example, in most of the cosmologically favored parameter space, the vector mesons are naturally long-lived and produce Standard Model particles in their decays. Electron and proton beam fixed-target experiments such as HPS, SeaQuest, and LDMX can exploit these signals to explore much of the viable parameter space. We also comment on dark matter decay inherent in a large class of previously considered models and explain how to ensure dark matter stability.
Highlights
Despite the wealth of gravitational evidence for dark matter (DM), its nature remains a fundamental puzzle in particle physics
In the weakly interacting massive particle (WIMP) paradigm, this occurs through annihilations to standard model (SM) particles
Once the temperature drops below the DM mass, any process that reduces the DM number density can potentially lead to a viable freeze-out scenario
Summary
Despite the wealth of gravitational evidence for dark matter (DM), its nature remains a fundamental puzzle in particle physics. The strongly interacting sector necessarily includes heavier excitations, such as vector mesons, VD, the analogues of SM ρ mesons, which are expected to mix with the dark photon. SIMP models rely on significant chiral symmetry breaking to achieve sufficiently large 3πD → 2πD cross sections, so that one expects mVD ∼ mπD In this case, VD → πDπD decays are kinematically forbidden, and the semiannihilation [4] reaction, πDπD → πDVD followed by VD → SM, is often the primary process responsible for depleting the DM abundance. These vector mesons decay to πDlþl− final states with even longer lifetimes These distinctive signatures can be searched for at beam dump and fixed-target experiments. Cross-sections and decay rates, and Boltzmann equations are provided in Appendices A–C
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