Cosmological Perturbations and Observational Constraints on Spinor Field Quintessence Dark Energy

Abstract

We investigate the linear perturbation cosmology of a spinor-field realization of quintessence dark energy by implementing the model in the Einstein--Boltzmann solver \texttt{CLASS}. The model parameters are constrained using a Markov Chain Monte Carlo analysis with Pantheon$^{+}$ Type Ia supernovae, cosmic chronometers, DESI DR2 baryon acoustic oscillations, redshift-space distortions, and Planck 2018 CMB distance-prior data. For the full combined dataset, we obtain $w_{\rm de}=-0.9710^{+0.0206}_{-0.0206}$, $Ω_{m0}=0.2939^{+0.0047}_{-0.0047}$, and $H_0=66.23^{+0.55}_{-0.53},\mathrm{kms^{-1}Mpc^{-1}}$. The corresponding perturbation quantities are $σ_8=0.7537^{+0.0076}_{-0.0075}$ and $S_8=0.7459^{+0.0067}_{-0.0065}$. We find that the spinor-quintessence model closely reproduces the predictions of a phenomenological constant-$w$ model in the matter power spectrum, growth-rate observable $fσ_8$, growth index, and CMB temperature anisotropy spectrum, with deviations generally below the percent level. A comparison with $Λ$CDM and $w$CDM shows statistically indistinguishable fits, although the Bayesian information criterion favors the simpler $Λ$CDM model. Our results demonstrate that the spinor-field quintessence scenario remains consistent with current expansion-history and structure-growth observations when its perturbation evolution is treated consistently, providing a field-theoretically motivated realization of constant-$w$ dark energy at the background and linear perturbation levels.