Revisiting Weak Energy Condition and wormholes in Brans-Dicke gravity

It is known that the formation of a wormhole typically involves a violation of the Weak Energy Condition (WEC), but the reverse is not necessarily true. In the context of Brans-Dicke gravity, the generalized Campanelli-Lousto solution, which we shall unveil in this paper, demonstrates a WEC violation that coincides with the appearance of unbounded sheets of spacetime within the region where $0<r<r_{\text{s}}$. The emergence of a wormhole in the region where $r>r_{\text{s}}$ is thus only an indirect consequence of the WEC violation. Whereas the two regions, $0<r<r_{\text{s}}$ and $r>r_{\text{s}}$, in general are disconnected by physical singularities at $r=r_{\text{s}}$, they are both part of the same mathematical solution, and their behavior can provide insights into the WEC, which is a mathematical property of the solution. Furthermore, we utilize the generalized Campanelli-Lousto solution to construct a Kruskal-Szekeres diagram, which exhibits a “gulf” sandwiched between the four quadrants in the diagram, a novel feature in Brans-Dicke gravity. Overall, our findings shed new light onto a complex interplay between the WEC and wormholes in the Brans-Dicke theory.