IAS Quantum Aspects of Black Holes Group Meeting

Abstract: This will be a mini-talk to explain the following. In a Euclidean path integral on a manifold X with many boundaries, which boundaries are associated with bras and which with kets? In a theory with no time-reversal symmetry, the answer involves keeping track of orientations. Time-reversal symmetry, when present, implies that spacetime need not be oriented but the distinction between bras and kets is inessential.