Generalized theories of gravity and conformal continuations: electrically charged systems

Summary: "Many theories of gravity admit formulations in different, conformally related manifolds, known as the Jordan and Einstein frames. Among them are scalar-tensor theories (STT) of gravity and theories with the Lagrangian f(R) where f is an arbitrary function. A singularity in the Einstein frame may correspond to a regular surface {Bbb S}_{rm trans} in the Jordan frame, and the solution is then continued beyond this surface. This phenomenon is called a conformal continuation (CC). We discuss the properties of CCs in static, spherically symmetric configurations with an electric charge in STT and f(R) theories of gravity and indicate necessary and sufficient conditions for the existence of CCs. Two cases are distinguished, when {Bbb S}_{rm trans} is an ordinary regular sphere and when it is a Killing horizon."