Late-Time Background Expansion and Cosmographic Signatures of Finsler-Randers-Sasaki Cosmology

Abstract

In this work, we investigate the late-time expansion history and geometric diagnostics of logarithmic and exponential Finsler--Randers--Sasaki (FRS) cosmological models. We constrain both scenarios using cosmic chronometers, Baryon acoustic oscillations, and Pantheon+ Type~Ia supernovae, considering baseline fits as well as configurations calibrated with the local SH0ES distance-ladder prior. In the uncalibrated case, both profiles provide consistent descriptions of the late-time expansion history. Incorporating the SH0ES prior increases the inferred Hubble constant and modifies the inferred acoustic scale, reflecting the interplay between the local distance-ladder calibration and the BAO distance scale. Cosmographic reconstructions reveal a smooth transition from deceleration to acceleration at intermediate redshifts. Over the observationally relevant redshift range, both models exhibit a non-phantom, quintessence-like effective dark-energy sector. Finally, statefinder diagnostics distinguish the two FRS geometries: the logarithmic model remains relatively close to the canonical flat $Λ\mathrm{CDM}$ fixed point, whereas the exponential model follows a distinct dynamical trajectory. These results demonstrate that, despite their similar background expansion histories, the two FRS constructions can exhibit substantially different higher-order kinematic signatures.