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Logarithmic and Strong Coupling Models in Weyl-Type $f(Q,T)$ Gravity

Rahul Bhagat, S. K. Tripathy, B. Mishra

TL;DR

This work explores late-time cosmology in Weyl-type f(Q,T) gravity, coupling the nonmetricity scalar Q to the trace T of the energy-momentum tensor within Weyl geometry. It analyzes two concrete forms, a logarithmic model and a strong coupling model, and solves the resulting equations numerically after reformulation in redshift, constraining the parameters with MCMC against CC, Pantheon Plus, Union3.0, and DESI DR2 data. The results show a transition from decelerated to accelerated expansion, with both models mimicking Lambda CDM at late times while exhibiting quintessence-like or phantom-like features depending on the model; NEC, WEC, and DEC are satisfied whereas SEC is violated in the recent epoch. The analysis yields universe ages consistent with Planck and stellar ages, and diagnostics like Om(z) and statefinders (r,s) support a dynamical dark energy picture arising from geometric modifications rather than a cosmological constant.

Abstract

In this paper, we have explored the cosmological implications of Weyl-type $f(Q,T)$ gravity, a modified gravitational theory formulated from Weyl geometry. The nonmetricity scalar $Q$ is coupled to the trace $T$ of the energy-momentum tensor. We analyze two models based on the logarithmic and strong coupling form of the function $f(Q,T)$. The corresponding field equations are then solved numerically after reformulating the system in terms of redshift. We used combined dataset from Cosmic Chronometers (CC), Pantheon$^+$ supernovae, and Baryon Acoustic Oscillations (BAO) and performed the Markov Chain Monte Carlo (MCMC) analysis to constrain the model parameters. Using the constrained parameters, the geometrical and dynamical aspects of the models are analyzed. The results successfully describe a transition from decelerated to accelerated expansion for both the models. The models mostly exhibit quintessence-like behavior and asymptotically approach the $Λ$CDM scenario at late times. The calculated age of the Universe from each model aligns with constraints from Planck and stellar age data. The violation of the strong energy condition and the satisfaction of null energy condition and dominant energy conditions are shown.

Logarithmic and Strong Coupling Models in Weyl-Type $f(Q,T)$ Gravity

TL;DR

This work explores late-time cosmology in Weyl-type f(Q,T) gravity, coupling the nonmetricity scalar Q to the trace T of the energy-momentum tensor within Weyl geometry. It analyzes two concrete forms, a logarithmic model and a strong coupling model, and solves the resulting equations numerically after reformulation in redshift, constraining the parameters with MCMC against CC, Pantheon Plus, Union3.0, and DESI DR2 data. The results show a transition from decelerated to accelerated expansion, with both models mimicking Lambda CDM at late times while exhibiting quintessence-like or phantom-like features depending on the model; NEC, WEC, and DEC are satisfied whereas SEC is violated in the recent epoch. The analysis yields universe ages consistent with Planck and stellar ages, and diagnostics like Om(z) and statefinders (r,s) support a dynamical dark energy picture arising from geometric modifications rather than a cosmological constant.

Abstract

In this paper, we have explored the cosmological implications of Weyl-type gravity, a modified gravitational theory formulated from Weyl geometry. The nonmetricity scalar is coupled to the trace of the energy-momentum tensor. We analyze two models based on the logarithmic and strong coupling form of the function . The corresponding field equations are then solved numerically after reformulating the system in terms of redshift. We used combined dataset from Cosmic Chronometers (CC), Pantheon supernovae, and Baryon Acoustic Oscillations (BAO) and performed the Markov Chain Monte Carlo (MCMC) analysis to constrain the model parameters. Using the constrained parameters, the geometrical and dynamical aspects of the models are analyzed. The results successfully describe a transition from decelerated to accelerated expansion for both the models. The models mostly exhibit quintessence-like behavior and asymptotically approach the CDM scenario at late times. The calculated age of the Universe from each model aligns with constraints from Planck and stellar age data. The violation of the strong energy condition and the satisfaction of null energy condition and dominant energy conditions are shown.

Paper Structure

This paper contains 7 sections, 49 equations, 10 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Field Equations of Weyl type $f(Q,T)$ gravity
  3. Cosmological Datasets
  4. The Cosmological Models
  5. Summary and Conclusion
  6. Model I Log Model
  7. Model II: Strong coupling Model

Figures (10)

  • Figure 1: The contour plots for the Logarithmic (Left Panel) and the Strong coupling (Right Panel) model CC dataset, Union3.0, Pantheon$^+$ dataset and DESI DR2 dataset data upto 2$-\sigma$ errors for the parameters.
  • Figure 2: Evolution of Hubble parameter for both the model.
  • Figure 3: Behavior of matter energy density. Logarithmic: Left Panel, Strong Coupling: Right Panel.
  • Figure 4: Behavior of Deceleration Parameter with redshift. Logarithmic: Left Panel, Strong Coupling: Right Panel.
  • Figure 5: Behavior of Equation of State Parameter with redshift. Logarithmic: Left Panel, Strong Coupling: Right Panel.
  • ...and 5 more figures