Constraining Cosmological Parameters From Statistical Superluminal Effects Without a Distance Ladder

Abstract

We employ a statistical approach to study apparent superluminal motion of luminous sources in an expanding flat Friedmann--Lemaître--Robertson--Walker universe, explicitly incorporating cosmological effects through the comoving distance at the emission time. Probability Density Functions (PDFs) of the apparent angular velocity are derived under minimal assumptions regarding source orientations and intrinsic peculiar velocity distributions. We show that the apparent angular velocity distributions and their associated statistical observables are sensitive to cosmological parameters $Ω_{Λ,0}$ and the Hubble parameter $H_0$. Using suitably defined observables, we construct correlated constraints in the $(Ω_{Λ,0}, H_0)$ parameter space and demonstrate that combining measurements at different redshifts effectively breaks the resulting degeneracy. Apparent superluminal motion thus provides a complementary kinematic consistency test for cosmological models.