Geometric interpretation of Thiemann's generalized Wick transform

TL;DR

This paper demonstrates that Thiemann's generalized Wick transform in vacuum gravity can be understood as an analytic continuation in explicit time dependence, with a specific transformation rule for the metric, applicable in various models and the general case.

Contribution

It provides a rigorous interpretation of Thiemann's generalized Wick transform as an analytic continuation and inverse Wick rotation in vacuum gravitational systems, extending previous understanding.

Findings

The transform maps Euclidean to Lorentzian metrics with an imaginary factor.

The transformation rule differs from a simple inverse Wick rotation in four-metric rescaling.

The interpretation applies to general vacuum gravity without model reduction or gauge fixing.

Abstract

In the Ashtekar and geometrodynamic formulations of vacuum general relativity, the Euclidean and Lorentzian sectors can be related by means of the generalized Wick transform discovered by Thiemann. For some vacuum gravitational systems in which there exists an intrinsic time variable which is not invariant under constant rescalings of the metric, we show that, after such a choice of time gauge and with a certain identification of parameters, the generalized Wick transform can be understood as an analytic continuation in the explicit time dependence. This result is rigorously proved for the Gowdy model with the topology of a three-torus and for a whole class of cosmological models that describe expanding universes. In these gravitational systems, the analytic continuation that reproduces the generalized Wick transform after gauge fixing turns out to map the Euclidean line element to the Lorentzian one multiplied by an imaginary factor; this transformation rule differs from that expected for an inverse Wick rotation in a complex rescaling of the four-metric. We then prove that this transformation rule for the line element continues to be valid in the most general case of vacuum gravity with no model reduction nor gauge fixing. In this general case, it is further shown that the action of the generalized Wick transform on any function of the gravitational phase space variables, the shift vector, and the lapse function can in fact be interpreted as the result of an inverse Wick rotation and a constant, imaginary conformal transformation.