This is a review of the fascinating topic of infrared divergences in inflation, on which there has recently been a lot of work. Particularly interesting was the suggestion to use the operator product expansion formalism of Hollands and Wald (0803.2003 and 0805.3419) to settle the issue of renormalisation of inflationary perturbations raised by Agullo et al (0901.0439, 1005.2727).
It would have been nice if the paper had also discussed the interesting work by Tsamis and Woodard on cancelling the effect of a cosmological constant by the backreaction produces infrared gravitons, which combines a possible solution to the cosmological constant problem with a simple inflationary scenario (hep-ph/9602315, hep-ph/9602316, astro-ph/9803172).
[1005.1649] Infrared effects in inflationary correlation functions
|Abstract:||In this article, I briefly review the status of infrared effects which occur when using inflationary models to calculate initial conditions for a subsequent hot, dense plasma phase. Three types of divergence have been identified in the literature: secular, "time-dependent" logarithms, which grow with time spent outside the horizon; "box-cutoff" logarithms, which encode a dependence on the infrared cutoff when calculating in a finite-sized box; and "quantum" logarithms, which depend on the ratio of a scale characterizing new physics to the scale of whatever process is under consideration, and whose interpretation is the same as conventional field theory. I review the calculations in which these divergences appear, and discuss the methods which have been developed to deal with them.|
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