Spinor-Field Realization of Modified Chaplygin Gas Dark Energy in FLRW Cosmology and Observational Constraints

This work investigates a nonlinear spinor field unified dark energy model in a spherically symmetric Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime, where the spinor self-interaction naturally reproduces a Modified Chaplygin Gas (MCG) equation of state. Unlike scalar-field or ΛCDM models, the spinor field generates non-diagonal components of the energy–momentum tensor as a consequence of spacetime geometry, providing new insight into the coupling between spinor dynamics and cosmic expansion. We confront the model with recent late-time observations, including cosmic chronometer measurements of H ( z ), Type Ia supernovae from the Pantheon+ compilation, and baryon acoustic oscillations (DESI DR2). A Markov Chain Monte Carlo analysis yields tight constraints on the model parameters, with a best-fit Hubble constant H 0 ≃ 67.78 km s − 1 Mpc − 1 . The model reproduces late-time cosmic acceleration with a present-day deceleration parameter q ( 0 ) ≃ − 0.493 and yields information criteria values that are competitive with ΛCDM. These results demonstrate that the spinor-field realization of MCG provides a viable and geometrically enriched alternative to standard dark energy scenarios.