It has recently been suggested that Planck scale physics may effect theevolution of cosmological fluctuations in the early stages of cosmologicalinflation in a non-trivial way, leading to an excited state for modes whosewavelength is super-Planck but sub-Hubble. In this case, the issue of how thisexcited state back-reacts on the background space-time arises. In fact, it hasbeen suggested that such back-reaction effects may lead to tight constraints onthe magnitude of possible deviations from the usual predictions of inflation.In this note we discuss some subtle aspects of this back-reaction issue andpoint out that rather than preventing inflation, the back-reaction ofultraviolet fluctuations may simply lead to a renormalization of thecosmological constant driving inflation.
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