Bayesian Inference of Neutron Star Properties in $f(Q)$ Gravity Using NICER Observations

TL;DR

This work tests neutron-star structure in symmetric teleparallel $f(Q)$ gravity using NICER mass–radius observations. It compares three representative models—Linear, Logarithmic, and Exponential—while fixing the dense-matter EoS to DDME2 to isolate gravitational effects, and it employs Bayesian inference to constrain model parameters and perform model comparison. The Exponential $f(Q)$ model emerges as statistically preferred, with $R_{1.4}=11.27^{+0.53}_{-0.36}$ km and $\Lambda_{1.4}=156.95^{+84.02}_{-41.73}$ for a canonical mass, indicating nonmetricity-driven deviations may be detectable in strong-field regimes. This approach demonstrates the potential of NS observations to probe symmetric teleparallel gravity beyond cosmology and highlights pathways for future joint gravity–EoS analyses and robustness checks against EoS systematics.

Abstract

In this work, we investigate neutron stars (NSs) in the strong field regime within the framework of symmetric teleparallel $f(Q)$ gravity, considering three representative models: linear, logarithmic, and exponential. While Bayesian studies of NS observations are well established in General Relativity and curvature based modified gravity theories, such analyses in $f(Q)$ gravity remain largely unexplored. We perform a Bayesian inference analysis by confronting theoretical NS mass-radius predictions with NICER observations of PSR J0030+0451, PSR J0740+6620, PSR J0437+4715, and PSR J0614+3329. The dense matter equation of state is fixed to DDME2 in order to isolate the effects of modified gravity on NS structure. Our results show that the exponential $f(Q)$ model is statistically preferred over the linear and logarithmic cases, as confirmed by Bayes factor comparisons, and exhibits well-constrained. For this model, we obtain a radius and tidal deformability at $1.4\,M_\odot$ of $R_{1.4} = 11.27^{+0.53}_{-0.36}\,\mathrm{km}$ and $Λ_{1.4} = 156.95^{+84.02}_{-41.73}$, respectively, consistent with current observational constraints. These results highlight the potential of NSs as powerful probes of symmetric teleparallel gravity in the strong field regime.

Figures (6)

• Figure 1: The energy density ($\epsilon$) (in MeV.fm$^{-3}$)(left panel), pressure ($P$) (in MeV.fm$^{-3}$) (middle panel), and speed of sound ($c_s^2$) (in $c^2$) (right panel) as a function of baryon density ($\rho$) (in fm$^{-3}$) for DDME2.
• Figure 2: The marginalized posterior distributions of the $f(Q)$ model parameters, obtained through Bayesian inference, for Linear (red), Logarithmic (purple), and Exponential (green) models. The vertical lines indicate the 68% confidence interval of the parameters. The confidence ellipses for two-dimensional posterior distributions are plotted with 1$\sigma$, 2$\sigma$ and 3$\sigma$confidence intervals.
• Figure 3: Corner plots for the marginalized posterior distributions (salmon) of the tidal deformability $\Lambda_{1.4}$, radii $R_{1.4}$ (km) and $R_{2.07}$ (km) and the maximum mass $M_{max}$ ($M_\odot$) for Linear (red), Logarithmic (purple), and Exponential (green).
• Figure 4: The 95% confidence interval distributions for the radius $R$ (km) (left panel), tidal deformability $\Lambda$ (middle panel) and compactness $M/R$ (right panel) as a function of NS mass $M$ ($M_\odot$). The astrophysical observations incorporated in the Bayesian framework are also shown.
• Figure 5: The Pearson's correlation coefficients among parameters and selected NS properties for Linear (left panel), Logarithmic (Middle panel), and Exponential(right panel).