S-matrix bootstrap bounds on self-interacting dark matter
arXiv:2607.13141
The authors apply a dispersive S‑matrix bootstrap to weakly coupled scalar dark matter and derive stringent upper limits on its mass from the required self‑interaction cross section, finding bounds tighter than those from partial‑wave unitarity alone.
Abstract
Self-interacting dark matter turns the structure of galactic halos into a direct requirement on a low-energy scattering amplitude. We show that, for weakly coupled scalar dark matter, this requirement implies a much stronger mass bound on the dark matter particle than partial-wave unitarity alone. Using analyticity, crossing symmetry, locality and partial-wave unitarity, we compute the maximal allowed threshold amplitude with a dispersive primal S-matrix bootstrap, assuming only a weakly coupled EFT below a scale and allowing arbitrary UV particle content above . For the benchmark self-interaction cross section , the mass of a generic weakly coupled scalar satisfies in the controlled EFT regime. If dark matter is a derivative-dominated pseudo-Nambu-Goldstone boson, the mass bound is lowered to the MeV scale or below, depending on the hierarchy .
6 pages, 3 figures