Observational constraints on f(Q,T) gravity from the mass-radius relation and stability of compact stars

TL;DR

This study investigates how pressure anisotropy affects compact-star structure in f(Q,T) gravity using a linear form f(Q,T) = ψ1 Q + ψ2 T. By solving the modified field equations for an anisotropic fluid in static spherically symmetric spacetimes and applying boundary conditions, the authors obtain a closed-form interior solution and analyze stability through causality, adiabatic index, and a modified TOV equation. The results show the model is non-singular and can account for observed pulsars with M > 2 M_sun as well as objects in the GW190814 mass gap, with radii predicted in the range 10.5–14.5 km for ψ1 ≤ 1.05 and PSR J0740+6620 around 13–14.7 km. The work demonstrates how the parameters ψ1, ψ2, and β control density, pressures, anisotropy, and mass–radius relations, offering observational constraints on f(Q,T) gravity in the strong-field regime.

Abstract

In this investigation we examine the astrophysical consequences of the influence of pressure anisotropy on the physical properties of observed pulsars within the background of $f(Q,T)$ gravity by choosing a specific form $f(Q, T)=ψ_1\, Q + ψ_2 T$, where $ψ_1$ and $ψ_2$ are the model parameters. Initially, we solve the modified field equations for anisotropic stellar configurations by assuming the physically valid metric potential along with anisotropic function for the distribution of the interior matter. We test the derived gravitational model subject to various stability conditions to confirm physically existence of compact stars within the $f(Q,T)$ gravity context. We analyze thoroughly the influence of anisotropy on the effective density, pressure and mass-radius relation of the stars. The present inspection of the model implies that the current gravitational models are non-singular and able to justify for the occurrence of observed pulsars with masses exceeding 2 $M_{\odot}$ as well as masses fall in the {\em mass gap} regime, in particular merger events like GW190814. The predicted radii for the observed stars of different masses fall within the range \{10.5 km, 14.5 km\} for $ψ_1\leq 1.05$ whereas the radius of PSR J074+6620 is predicted to fall within \{13.09 km, 14.66 km\} which is in agreement with the predicted radii range \{11.79 km, 15.01 km\} as can be found in the recent literature.

Figures (9)

• Figure 1: Impact of parameters $\psi_1$, $\psi_2$, and $\beta$ on the energy density ($\rho^{\text{eff}}$) against the radial distance $r$ for $\mathcal{X} =0.0016\, \text{km}^{-2}$ with fixed values: (i) $\psi_2=0.5$ and $\beta=0.5$ for left panel, (ii) $\psi_1=0.8$ and $\beta=0.5$ for middle panel, and (iii) $\psi_1= 0.9$ and $\psi_2=0.5$ for right panel.
• Figure 2: Impact of parameters $\psi_1$, $\psi_2$, and $\beta$ on the radial and tangential pressures ($p^{\text{eff}}_r$ & $p^{\text{eff}}_t$) against the radial distance $r$. For these plots, we select the same data set of values as used in Fig. \ref{['f1']}.
• Figure 3: Impact of parameters $\psi_1$, $\psi_2$, and $\beta$ on the anisotropy ($\Delta^{\text{eff}}$) against the radial distance $r$. For these plots, we select the same data set of values as used in Fig. \ref{['f1']}.
• Figure 4: Impact of parameters $\psi_1$, $\psi_2$, and $\beta$ on the velocity of sounds ($\text{v}^2_r$ & $\text{v}^2_t$) against radial distance $r$ for $\mathcal{X} =0.0016\, \text{km}^{-2}$ with fixed values: (i) $\psi_2=0.5$ and $\beta=0.5$ for left panel, (ii) $\psi_1=0.8$ and $\beta=0.5$ for middle panel, and (iii) $\psi_1= 0.9$ and $\psi_2=0.5$ for right panel.
• Figure 5: Impact of parameters $\psi_1$, $\psi_2$, and $\beta$ on the adiabatic index ($\Gamma$) against radial distance $r$$\mathcal{X} =0.0016\, \text{km}^{-2}$ with fixed values: (i) $\psi_2=0.5$ and $\beta=0.5$ for left panel, (ii) $\psi_1=0.8$ and $\beta=0.5$ for middle panel, and (iii) $\psi_1= 0.9$ and $\psi_2=0.5$ for right panel.