A Casimir obstruction to asymptotically flat black-brane completions of non-supersymmetric 7-branes

A bstract We study axisymmetric 7-brane solutions in the dilaton-gravity sector of 10d supergravity, including the backreaction of the Casimir energy induced by monodromies around the transverse circle. Without Casimir energy, we find that the system is analytically solvable and admits locally flat asymptotics with arbitrary deficit angles, but the corresponding solutions contain a naked singularity at finite proper distance. We investigate whether this singularity can be replaced by a regular finite-horizon black-brane core once Casimir backreaction is included. We find that, within our ansatz, Casimir backreaction obstructs an asymptotically locally flat black-brane completion of the naked 7-brane solution.