Composite Inelastic Dark Matter
Daniele S. M. Alves, Siavosh R. Behbahani, Philip Schuster, Jay G. Wacker
TL;DR
The paper addresses the DAMA annual modulation and the challenge of explaining it within a viable dark-matter framework. It proposes Composite Inelastic Dark Matter (CiDM), where dark matter is a meson from a confining SU(N_c) sector containing a heavy Psi_H and a light Psi_L, with a spin-0 pi_d state and a nearly degenerate spin-1 rho_d, and a hyperfine splitting set by the strong dynamics. An axial U(1)_{A'} mediator kinetically mixes with hypercharge to induce inelastic hyperfine transitions pi_d → rho_d that reproduce DAMA's signal, while elastic channels are suppressed by parity. The authors compute the low-energy scattering, perform a global fit to DAMA's spectrum and null searches, and discuss cosmological viability via a dark-meson number asymmetry with rho_d de-excitation and self-interactions within astrophysical bounds. The framework yields testable predictions for direct detection spectral shape and collider searches for the GeV-scale A' mediator, offering a concrete path to validate or falsify CiDM as an explanation for DAMA.
Abstract
Peaking consistently in June for nearly eleven years, the annual modulation signal reported by DAMA/NaI and DAMA/LIBRA offers strong evidence for the identity of dark matter. DAMA's signal strongly suggest that dark matter inelastically scatters into an excited state split by O(100 keV). We propose that DAMA is observing hyperfine transitions of a composite dark matter particle. As an example, we consider a meson of a QCD-like sector, built out of constituent fermions whose spin-spin interactions break the degeneracy of the ground state. An axially coupled U(1) gauge boson that mixes kinetically with hypercharge induces inelastic hyperfine transitions of the meson dark matter that can explain the DAMA signal.