Unveiling Structural Discrepancies: A Manifold and Information-Theoretic Comparison of Gravitational Waveform Posteriors for GW231123

Abstract: Gravitational-wave parameter inference critically depends on waveform models, but current comparisons often overlook significant high-dimensional structural differences in posterior distributions by focusing solely on one-dimensional marginals. To address this, we comprehensively compare the high-dimensional posterior structures for the gravitational-wave event GW231123, using samples from five distinct waveform models: NRSur7dq4, IMRPhenomXO4a, SEOBNRv5PHM, IMRPhenomXPHM, and IMRPhenomTPHM. Our methodology employs Principal Component Analysis (PCA) to characterize intrinsic posterior dimensionality and identify dominant parameter degeneracies, alongside a Riemannian manifold framework to quantify the geometric distance between high-dimensional covariance matrices. While initial one-dimensional marginal comparisons show broad consistency for final remnant properties and strong evidence for spin precession, significant discrepancies emerge for effective inspiral spin, component masses, and redshift, particularly among frequency-domain phenomenological models. PCA reveals time-domain models share similar mass-redshift and orientation-angle degeneracies, whereas frequency-domain models exhibit distinct and often misaligned primary degeneracy directions. Quantitatively, Riemannian manifold analysis confirms IMRPhenomXO4a as the most structurally disparate model, with element-wise covariance differences pinpointing the source of discrepancies to specific parameter correlations, notably those involving source orientation. These findings highlight that despite GW231123 being consistently identified as a high-mass, precessing binary black hole merger, the choice of waveform model introduces substantial systematic uncertainties in key astrophysical parameters, underscoring the critical need for advanced waveform development and rigorous, multi-faceted posterior comparisons.

Subjects:	astro-ph.CO; cs.LG
Cite as:	PX:2508.00011