Issues about Cosmological Ward Identities

TL;DR

This paper explores the derivation of cosmological Ward identities through the local introduction of Noether currents in path integrals, analyzing gauge fixing in gravity-scalar systems and connecting residual symmetries to cosmological consistency relations.

Contribution

It provides a detailed analysis of residual symmetries in gauge-fixed gravity-scalar systems and derives the associated Ward identities relevant for cosmological perturbations.

Findings

Residual dilatation symmetry leads to a conserved charge.

The conserved charge is expressed as a surface integral at infinity.

Ward identities reproduce standard cosmological consistency relations.

Abstract

In this paper we first discuss how a Noether current corresponding to a gauge or a global symmetry can locally be introduced in a path integral irrespective of the boundary conditions defining the theory. We then consider quantization of gravity plus minimally coupled scalar field system in the phase space path integral approach. The complete gauge fixed action including the Faddeev-Popov determinant is obtained in the so called $\zeta$-gauge. It turns out that in this formalism while the dilatation survives as the residual symmetry of the gauge fixed action, other diffeomorphisms which require field dependent corrections fail to be so. The full Noether current for the dilatation is determined and the spatial boundary conditions that yield a finite and conserved charge are determined. The charge is shown to be expressible as a surface integral at infinity and the corresponding Ward identity gives the standard consistency relation of cosmological perturbations.