Morris-Thorne Wormholes in $f(R,T)$ modified theory of gravity
We study static traversable wormholes obtained by Morris and Thorne in general relativity (GR) in the framework of a modified theory of gravity. The modified gravitational action $f(R,T)$ is a function of the Ricci scalar ($R$) and of the trace of the energy momentum tensor ($T$). For a modified gravity $f(R,T)=R+\alpha R^{2}+\lambda T$, where $\alpha$ and $\lambda$ are constants, we obtain wormhole solutions (WH) with normal matter for a relevant shape functions. The energy conditions are checked at the throat and away from the throat of the WH. The coupling parameters $\alpha $ and $\lambda$ in the gravitational action play an important role to accommodate the matter composition. For a given $\lambda$, WH solutions are found in the presence of exotic matter at the throat for $\alpha <0$. It is shown that WH exists in the modified gravity without exotic matter when $\alpha >0$. We consider two different shape functions to investigate the existence of WH in the presence of exotic or normal matter. A class of WH solutions exist with anisotropic fluid provided $\lambda \neq - 8 \pi$. In flat asymptotic regions on both sides of the throat with anisotropic source and $\lambda= - 8 \pi$, it does not permit WH as per no go theorem. As $\lambda \rightarrow 0$ in the gravitational action, all the energy conditions are obeyed with the hybrid shape function indicating existence of WH with normal matter.