Cosmic dynamics and dark energy evolution in scalar-tensor theories on Finsler-like tangent bundles with observational constraints

We investigate a scalar-tensor cosmological model formulated on a Lorentzian tangent bundle endowed with a Finsler-like geometric structure. By employing a Sasaki-type metric with a dynamically evolving scalar field, we derive modified gravitational field equations that naturally incorporate anisotropic corrections to standard general relativity. Applying this framework to a spatially flat FLRW background, we obtain generalized Friedmann equations and identify effective dark energy density and pressure terms emerging from the geometry. Using a parameterized form of the scalar field ϕ(z)=α(1+z)+β, we reconstruct the Hubble expansion rate and confront the model with observational data from Cosmic Chronometers, DESI BAO, and Type Ia Supernovae (Pantheon+SH0ES and DES-Y5) using MCMC analysis. The best-fit results yield tight constraints on the model parameters, with the Hubble constant found to be H0=69.17±0.46 km/s/Mpc (Pantheon+SH0ES) and H0=68.90±0.48 km/s/Mpc (DES-Y5), and the dark energy equation of state as ωDE=−0.925±0.059 and ωDE=−0.987±0.066, respectively, indicating phantom-like behavior. The matter density parameter is consistently constrained to Ωm0=0.316±0.020. The analysis of deceleration, jerk, and snap parameters highlights the model ability to explain cosmic acceleration. Reconstructed diagnostics including Om(z), statefinder parameters {r,s}, and the dark energy density parameter ΩDE(z) reveal a transition from matter domination to late-time acceleration that mimics ΛCDM but originates from intrinsic geometric corrections. Furthermore, the scalar potential V(ϕ) is reconstructed, showing behavior consistent with a quintessence-like evolving field. These results demonstrate that the proposed Finsler-inspired scalar-tensor framework provides a viable and observationally consistent alternative to standard dark energy models.