Covariant two point function for minimally coupled scalar field in de Sitter space-time

TL;DR

This paper constructs a covariant, infrared divergence-free two-point function for a minimally coupled scalar field in de Sitter space, emphasizing the role of negative norm states for covariant quantization and renormalization.

Contribution

It provides an explicit, gauge-invariant construction of the two-point function free of infrared divergences, completing previous work on covariant quantization in de Sitter space.

Findings

Two-point function is free of infrared divergence.

Covariant quantization involves negative norm states.

Green's functions are gauge invariant and coordinate independent.

Abstract

In a recent paper [1], it has been shown that negative norm states are indispensable for a fully covariant quantization of the minimally coupled scalar field in de Sitter space. Their presence, while leaving unchanged the physical content of the theory, offers an automatic and covariant renormalization of the vacuum energy divergence. This paper is a completion of our previous work. An explicit construction of the covariant two-point function of the ``massless'' minimally coupled scalar field in de Sitter space is given, which is free of any infrared divergence. The associated Schwinger commutator function and retarded Green's function are calculated in a fully gauge invariant way, which also means coordinate independent.