T-duality across event horizons

When applying T-duality to a generic, non-extreme event horizon, T-duality is spacelike on one side and timelike on the other. We will show using simple examples from four-dimensional Einstein-Maxwell theory, that the image of the horizon is a singularity which can be understood as an interface between two different T-dual theories and their solutions. Using an embedding into type-II string theory, we will get further insight into the nature of this singularity.

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