Bra-ket wormholes and Casimir entropy

Bra-ket wormholes are non-trivial saddles in Euclidean gravity. They have to be sustained by negative Casimir energy of matter fields inside the throat. However, Casimir energy is very sensitive to boundary conditions and in presence of gauge symmetries one has to integrate over all possible boundary conditions for the matter fields, as they are a part of bra-ket wormhole moduli. For non- Abelian gauge groups the corresponding measure for the boundary conditions, which we call Casimir entropy, is non-trivial and it competes with the Casimir energy. We find that for large gauge groups this significantly affects the bra-ket wormhole action and modifies the phase diagram. Despite that, we do not find any violations of strong subadditivity in the setup proposed by Chen, Gorbenko and Maldacena.