Observational Constraints on Chaplygin Gas Models in Non-Minimally Coupled Power Law $f(Q)$ Gravity with Quasars

TL;DR

This work investigates non-minimally coupled power-law $f(Q)$ gravity in a flat FLRW universe with a background comprising baryons, radiation, and three Chaplygin-gas variants (GCG, MCG, VCG). The authors derive the cosmological field equations for $f_1(Q)=\alpha Q^m$ and $f_2(Q)=Q$, and constrain the models using OHD, BAO, and cosmology-independent-calibrated QSO data via MCMC. They find transition redshifts $z_t$ of $0.620^{+0.018}_{-0.017}$ (GCG), $0.537^{+0.017}_{-0.017}$ (MCG), and $0.470^{+0.012}_{-0.012}$ (VCG), indicating departures from $\Lambda$CDM, with GCG closest to the standard model. Information criteria show moderate support for GCG while MCG and VCG are disfavored relative to $\Lambda$CDM, underscoring the potential of CG components in modified gravity contexts but also the dominance of $\Lambda$CDM given current data. The analysis demonstrates that incorporating QSO data with cosmic chronometers and BAO provides tighter constraints and reveals nuanced differences among CG models in the context of non-minimally coupled $f(Q)$ gravity.

Abstract

In the framework of $f(Q)$ gravity, where gravity emerges from non-metricity $Q$, we explore the cosmological implications of its non-minimal coupling to matter. Inspired by the recent success of Chaplygin gas models in explaining dark energy, we consider a background fluid composed of baryonic matter, radiation, and a family of Chaplygin gas variants namely Generalized Chaplygin Gas (GCG), Modified Chaplygin Gas (MCG), and Variable Chaplygin Gas (VCG). We constrain these models with three recent observational datasets: Observational Hubble Data (OHD), Baryonic Acoustic Oscillation (BAO) measurements, and Quasi-Stellar Objects (QSO) data. For the QSO dataset, we propose an analytical expression for errors in comoving distance to circumvent the reliance on Monte Carlo simulations. Using kinematic diagnostics such as the deceleration and jerk parameters and Om diagnostic, we assess deviations of the proposed models from $Λ$CDM. Our joint analysis of the three datasets reveals that the transition redshift from a decelerated to an accelerated expansion of the universe for the GCG, MCG and VCG models is $0.620^{+0.018}_{-0.017}$, $0.537^{+0.017}_{-0.017}$ and $0.470^{+0.012}_{-0.012}$ respectively, indicating a departure from $Λ$CDM.

Figures (6)

• Figure 1: The corner plot above displays one-dimensional marginalized distributions and the two-dimensional contour plots for the free parameters of the GCG model with $1-\sigma$ and $2-\sigma$ error bands obtained with EMCEE using OHD+BAO+QSO.
• Figure 2: The corner plot above displays one-dimensional marginalized distributions and the two-dimensional contour plots for the free parameters of the MCG model with $1-\sigma$ and $2-\sigma$ error bands obtained with EMCEE using OHD+BAO+QSO.
• Figure 3: The corner plot above displays one-dimensional marginalized distributions and the two-dimensional contour plots for the free parameters of the VCG model with $1-\sigma$ and $2-\sigma$ error bands obtained with EMCEE using OHD+BAO+QSO.
• Figure 4: (a) Hubble parameter against redshift $z$. The solid line represents EMCEE fit of the proposed model to the $57$ datapoints of $H(z)$ dataset. $\Lambda$CDM model is indicated with the dashed-dot line. (b) Distance modulus $\mu(z)$ as a function of $z$. The circular scatter marker represents the EMCEE fit of the proposed model to the 2019 QSO data. $\Lambda$CDM model is indicated with the black dashed line.
• Figure 5: Plots of various diagnostics against redshift $z$ for our three models with the shaded regions representing the $1-\sigma$ uncertainty bands. Overall, the GCG model exhibits a behavior closely resembling that of the $\Lambda$CDM paradigm, with the overall strongest deviations observed in the MCG model.