Self-Interacting Dark Matter: From Particle Physics Theories to Structure Formation Simulations

Abstract

We establish a unified theory-to-simulation framework for self-interacting dark matter (SIDM) that integrates three components: (i) a comprehensive, self-contained treatment of its particle-physics foundations and a broad range of model classes; (ii) a systematic, quantitative mapping from microscopic dark-sector physics to structure-formation simulation inputs through explicit expressions and numerical prescriptions; and (iii) the development, implementation, and validation of a broad suite of SIDM algorithms and a dedicated DM decay module in the moving-mesh code AREPO-2. Under (i), we detail the particle content, symmetries, interactions, production mechanisms, and constraints of a broad landscape of elementary and composite SIDM models, and present representative viable benchmark models. Under (ii), the mapping specifies cosmological initial conditions, internal-state masses and populations, reaction networks, velocity- and angle-dependent cross sections, dissipative energy loss, and decay rates and recoil kinematics. We then apply this mapping to a broad range of SIDM model classes. Under (iii), we implement and validate SIDM algorithms with constant and velocity-dependent cross sections, covering isotropic and anisotropic scattering, multi-state elastic and inelastic reactions, and dissipative processes, alongside a dedicated DM decay module in AREPO-2. We validate these implementations through beam-lattice deflection experiments, thermalization and uniform-box decay tests, isolated-halo gravothermal core-collapse simulations, and cosmological box and zoom-in simulations. These tests recover analytical predictions, establish agreement across numerical schemes, and reproduce published benchmarks. Our theory-to-simulation framework serves as a cross-disciplinary reference and a practical bridge between SIDM particle physics and simulations of nonlinear structure formation.