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 $w_{\mathrm{de}}=-0.9710_{-0.0206}^{+0.0206}$, ${\Omega }_{m0}=0.2939_{-0.0047}^{+0.0047}$, and $H_0=66.23_{-0.53}^{+0.55},\mathrm{km}{\mathrm{s}}^{-1}\mathrm{Mp}{\mathrm{c}}^{-1}$. The corresponding perturbation quantities are ${\sigma }_8=0.7537_{-0.0075}^{+0.0076}$ and $S_8=0.7459_{-0.0065}^{+0.0067}$. 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 $f{\sigma }_8$, growth index, and CMB temperature anisotropy spectrum, with deviations generally below the percent level. A comparison with $\Lambda$CDM and $w$CDM shows statistically indistinguishable fits, although the Bayesian information criterion favors the simpler $\Lambda$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.

19 pages, 5 figures