Redshift_Tomography_KBC_Void_Zenodo_v1

Abstract

The KBC void—a ~20 billion light-year underdensity centered near the Milky Way—has emerged as a leading candidate explanation for the Hubble tension. Traditional characterization methods (galaxy counting, static BAO fitting) suffer from systematics including dust extinction and ambiguous boundary definitions, limiting size precision to ±30%. Here we introduce a redshift-tomographic framework that constrains void geometry by fitting the redshift evolution of the locally-inferred Hubble parameter H₀(z). Exploiting recent Pantheon+ supernova and DESI early-release data, we demonstrate that the dynamical response of the local expansion rate to the void's gravitational drag provides a clean separation of void contribution from cosmological background. Under three density profiles (Gaussian, Exponential, Maxwell-Boltzmann), we derive formal parameter constraints for void radius R and density contrast δ. Applying our framework, we obtain a void diameter of 19.84 ± 0.46 billion light-years (precision ±2.3%), a factor of ~13 improvement over galaxy counting. The framework is generalizable to other large-scale cosmic voids and establishes a new precision probe for near-field cosmology.