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

International audienceWe 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