Breaking the UV Luminosity Function Degeneracy:Self-Interacting Dark Matter Constraints from Reionization Topology

TL;DR

This paper demonstrates that 21 cm reionization topology can break degeneracies in constraining self-interacting dark matter (SIDM) properties, providing a robust method to probe dark matter microphysics independent of galaxy formation uncertainties.

Contribution

The study introduces a novel approach using reionization topology to constrain SIDM, overcoming limitations of UV luminosity function analyses.

Findings

21 cm reionization topology uniquely constrains SIDM properties.

Constant-cross-section SIDM with σ/m ≥ 1-2 cm²/g is either excluded or detectable.

Reionization morphology signatures are independent of star formation efficiency.

Abstract

Self-interacting dark matter (SIDM) is the leading framework resolving small-scale cold dark matter (CDM) crises, yet high-redshift SIDM constraints are fundamentally limited by degeneracies between dark matter microphysics and galaxy formation astrophysics. We demonstrate that the UV luminosity function alone cannot constrain SIDM: star formation suppression from SIDM halo core formation is fully absorbed by modest adjustments to standard astrophysical parameters. We show that 21 cm reionization topology breaks this degeneracy completely, providing a nuisance-immune probe: the SIDM-enhanced duty cycle of ionizing photon escape leaves a morphological signature fully independent of star formation efficiency. Combining JWST UVLF measurements with SKA1-Low forecasts, constant-cross-section SIDM with $\sigma/m \gtrsim 1$--$2\ \mathrm{cm^2/g}$ is either excluded or detectable across all physically motivated star formation coupling strengths. Our results establish a robust new avenue to probe dark matter microphysics in the early Universe.