Lorentzian condition in quantum gravity

Abstract

The wave function of the Universe is usually taken to be a functional of the three-metric on a spacelike section, $\ensuremath{\Sigma},$ which is measured. It is sometimes better, however, to work in the conjugate representation, where the wave function depends on a quantity related to the second fundamental form of $\ensuremath{\Sigma}.$ This makes it possible to ensure that $\ensuremath{\Sigma}$ is part of a Lorentzian universe by requiring that the argument of the wave function be purely imaginary. We demonstrate the advantages of this formalism first in the well-known examples of the nucleation of a de Sitter or a Nariai universe. We then use it to calculate the pair creation rate for sub-maximal black holes in de Sitter space, which had been thought to vanish semi-classically.