Self-Interacting Dark Matter as a Proxy for Structural Evolution

Self-interacting dark matter (SIDM) has emerged as one of the most successful phenomenological responses to long-standing small-scale structure tensions in cosmology, including the cusp–core problem, too-big-to-fail, and the diversity of galaxy rotation curves. While SIDM simulations reproduce a wide range of observed halo behaviors through gravothermal evolution, the microphysical origin of the required interaction cross-sections remains unconstrained and non-universal. In this work, we propose that this asymmetry is diagnostic rather than problematic. We argue that SIDM functions primarily as an effective structural proxy, emulating missing degrees of freedom in halo evolution related to damping, mediation, and constraint-driven redistribution of phase space. Under this interpretation, core formation, diversity, and apparent collapse reflect structural regime transitions rather than definitive evidence for dark matter particle scattering. This work neither confirms nor denies the existence of dark matter, and makes no ontological claim about its fundamental nature. This reframing preserves the empirical successes of SIDM while reducing ontological commitment, and it yields falsifiable predictions concerning environmental dependence, hysteresis, and correlated transitions across baryonic and non-baryonic channels. The results suggest that SIDM’s success may point less to new dark-sector forces than to incomplete structural modeling in collisionless treatments of gravitational systems.