Infrared behavior and gauge artifacts in de Sitter spacetime: The photon field

TL;DR

This paper investigates the infrared behavior of the photon field in de Sitter spacetime, revealing gauge-dependent variations and proposing a criterion to extract the physical, well-behaved two-point function.

Contribution

It demonstrates the gauge dependence of the IR behavior of the photon two-point function in de Sitter space and introduces a criterion to isolate the physical component.

Findings

IR behavior varies with gauge choice from vanishing to growing

A criterion for physical two-point function yields IR stability

Discrepancy with flat spacetime IR behavior is highlighted

Abstract

We study the infrared (long distance) behavior of the free photon field in de Sitter spacetime. Using a two-parameter family of gauge fixing terms, we show that the infrared (IR) behavior of the two-point function is highly gauge-dependent and ranges from vanishing to growing. This situation is in disagreement with its counterpart in flat spacetime, where the two-point function vanishes in the IR for any choice of the gauge fixing parameters. A criterion to isolate the "physical" part of the two-point function is given and is shown to lead to a well-behaved two-point function in the IR.