Stability Analysis of Cosmological models in $f(T,\phi)$ Gravity

Abstract

We investigated the stability condition in $f(T,\phi)$ gravity theory for considering two models by using dynamical system. We assume the forms of $G(T)$ are $(i)$ $G(T)$ = $\alpha T+\frac{\beta}{T}$, $(ii)$ $G(T)$ = $\zeta T$ ln$(\psi T)$, where $\alpha$, $\beta$, $\zeta$ and $\psi$ be the free parameters. We evaluated the equilibrium points for these models and examine the stability behavior. We found five stable critical points for Model I and three stable critical points for Model II. The phase plots for these systems are examined and discussed the physical interpretation. We illustrate all the cosmological parameters such as $\Omega_{m}$, $\Omega_{\phi}$, $q$ and $\omega_{Tot}$ at each fixed points and compare the parameters with observational values. Further, we assume hybrid scale factor and the equation of redshift and time is $t(z)=\frac{\delta}{\sigma}W\bigg[\frac{\sigma}{\delta}\bigg(\frac{1}{a_{1}(1+z)}\bigg)^{\frac{1}{\delta}}\bigg]$. We transform all the parameters in redshift by using this equation and examine the behavior of these parameters. Our models represent the accelerating stage of the Universe. The energy conditions are examined in terms of redshift and SEC is not satisfied for the model. We also find the statefinder parameters $\{r,s\}$ in terms of z and discuss the nature of $r-s$ and $r-q$ plane. For both pairs $\{r,s\}$ and $\{r,q\}$ our models represent the $\Lambda$CDM model. Hence, we determine that our $f(T,\phi)$ models are stable and it satisfies all the observational values.