On wormhole formation in $f(\textit{R}, \textit{T})$ gravity: varying Chaplygin gas and barotropic fluid

Abstract

Formation of specific static wormhole models is discussed, by assuming an $f(\textit{R}, \textit{T}) = R + 2 \lambda T$ extended theory of gravity, $T =- \rho + P_{r} + 2P_{l}$ being the trace of the energy momentum tensor. In the first part, wormhole solutions are constructed imposing that the radial pressure admits an equation of state corresponding to a varying Chaplygin gas. Two forms for the varying Chaplygin gas are considered, namely $P_{r} = - B b(r)^{u}/\rho^{\alpha}$ and $P_{r} = -B R(r)^{m}/ \rho^{\alpha }$, respectively. In the second part, the wormhole models are constructed assuming that the radial pressure can be described by a varying barotropic fluid. In particular, $P_{r} = \omega b(r)^{v} \rho$ and $P_{r} =\hat{ \omega} r^{k} R(r)^{\eta} \rho$ are considered, respectively, leading to two additional, traversable wormhole models. In all cases, $b(r)$ is the shape function, and $R(r)$ the Ricci scalar obtained from the wormhole metric for a redshift function equal to $1$. With the help of specific examples, it is demonstrated that the shape functions of the exact wormhole models previously constructed do obey the necessary metric conditions. The same energy conditions help reveal the physical properties of these models. A general feature is the violation of the NEC~($\rho + P_{i} \geq 0$) in terms of the radial pressure $P_{r}$ at the throat of the wormhole. For some of the models, one can satisfy the NEC at the throat while a violation of the DEC~($\rho - P_{i} \geq 0$) occurs. To summarize, exact wormhole models can be constructed with a possible violation of the NEC and DEC at the throat of the wormhole, while being $\rho \geq 0 $. Thus, the interesting feature appears that one has a violation of the WEC~($\rho \geq 0$ and $\rho + P_{i} \geq 0$) not related to the energy density behavior (the index i, being r resp. l, indicates radial resp. lateral pressure).