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Paper IPM / Astronomy / 14570  


Abstract:  
Stochastic effects in generic scenarios of inflation with multiple fields are investigated. First Passage Time techniques are employed to calculate the statistical moments of the number of inflationary efolds, which give rise to all correlation functions of primordial curvature perturbations through the stochastic ÃÂ´N formalism. The number of fields is a critical parameter. The probability of exploring arbitrarily largefield regions of the potential becomes nonvanishing when more than two fields are driving inflation. The mean number of efolds can be infinite, depending on the number of fields; for plateau potentials, this occurs even with one field. In such cases, correlation functions of curvature perturbations are infinite. They can however be regularised if a reflecting (or absorbing) wall is added at large energy or field value. The results are found to be independent of the exact location of the wall and this procedure is therefore welldefined for a wide range of cutoffs, above or below the Planck scale. Finally, we show that, contrary to singlefield setups, multifield models can yield large stochastic corrections even at subPlanckian energy, opening interesting prospects for probing quantum effects on cosmological fluctuations.
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