Dark matter shifts away from direct detection

Abstract

Dark matter could emerge along with the Higgs as a composite pseudo-Nambu-Goldstone boson χ with decay constant f∼ TeV. This type of WIMP is especially compelling because its leading interaction with the Standard Model, the derivative Higgs portal, has the correct annihilation strength for thermal freeze-out if mχ ∼ O(100) GeV, but is negligible in direct detection experiments due to the very small momentum transfer. The explicit breaking of the shift symmetry which radiatively generates mχ, however, introduces non-derivative DM interactions. In existing realizations a marginal Higgs portal coupling λ is generated with size comparable to the Higgs quartic, and thus well within reach of XENON1T . Here, we present and analyze the interesting case where the pattern of explicit symmetry breaking naturally suppresses λ beyond the reach of current and future direct detection experiments. If the DM acquires mass from bottom quark loops, the bottom quark also mediates suppressed DM-nucleus scattering with cross sections that will be eventually probed by LZ . Alternatively, the DM can obtain mass from gauging its stabilizing U(1) symmetry. No direct detection signal is expected even at future facilities, but the introduction of a dark photon γD has a number of phenomenological implications which we study in detail, treating mγD as a free parameter. Complementary probes of the dark sector include indirect DM detection, DM self-interactions, and extra radiation, as well as collider experiments. We frame our discussion in an effective field theory, motivating our parameter choices with a detailed analysis of an SO(7)/SO(6) composite Higgs model, which can yield either scenario at low energies.