Directional Systematics in Gravitational-Wave Parameter Estimation: Mass Inflation and Phase Impedance in the GWTC-3 Catalog

Recent population analyses of gravitational-wave transient catalogs rely on Bayesian inference pipelines that assume signal propagation through a perfectly isotropic and lossless Friedmann-Lemaître-Robertson-Walker (FLRW) metric. Unmodeled large-scale propagation effects may introduce algorithmic artifacts in matched-filtering parameter estimation. We investigate the parametric degeneracy inherent in Inspiral-Merger-Ringdown (IMR) templates when confronted with a phenomenological phase-impeding medium. We derive an analytical mapping demonstrating how unmodeled phase-drag translates directly into chirp mass inflation. Motivated by macroscopic optical dipoles, we adopt a phenomenological dispersive baseline of βdisp = 0.034 ± 0.010. Under this framework, we mathematically demonstrate that local binary black holes (z ≈ 0.19) would suffer a systematic mass inflation of +3.52%. Applying a Jacobian spatial transformation as a mathematical diagnostic, we illustrate how anisotropic destacking collapses the anomalous 35M⊙ peak reported in the GWTC-3 catalog. We present this mathematical framework to demonstrate that purported novel astrophysical subpopulations, such as hierarchical mergers, may be partially driven by systematic calibration biases, underscoring the critical need for complete hierarchical injections incorporating modified dispersion relations.