Cosmological insights from an exponential $Om(z)$ function in $f(T,T_G)$ gravity framework

Abstract

We examine a modified teleparallel gravity model defined by $f(T,T_G)=T+\gamma \sqrt{T_G}+\delta \sqrt{T}$ by introducing an exponential $Om(z)$ diagnostic of the form $Om(z)=\alpha e^{\frac{z}{1+z}}+\beta$. This novel form captures smooth redshift evolution and allows for a flexible, model-independent probe of dark energy dynamics. We derive a Hubble function from this expression and use MCMC analysis with $31$ CC, $26$ BAO and $1701$ Pantheon+ data points to constrain the model parameters. The best-fit results yield $H_0\in [68.46,77.38]$km/s/Mpc for $\alpha \in [-0.232,-0.068]$ and $\beta \in [0.218,0.560]$ which is consistent with local $H_0$ values. Our model predicts a transition redshift $z_{tr}\approx (0.48-0.54)$, present $q_0\approx -0.34$, and ${\omega }_0\approx -0.33$. It satisfies NEC and DEC, closely tracks $\Lambda$CDM in the statefinder plane and estimates a cosmic age of $(13.28-13.87)$ Gyr which confirms its strength in explaining late-time acceleration. Our findings demonstrate that the exponential $Om(z)$ parameterization provides a robust and insightful approach to trace dark energy evolution within modified gravity frameworks.

17 pages, 9 figures