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      Full nonlinear growing and decaying modes of superhorizon curvature perturbations

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          Abstract

          We clarify the behavior of curvature perturbations in a nonlinear theory in case the inflaton temporarily stops during inflation. We focus on the evolution of curvature perturbation on superhorizon scales by adopting the spatial gradient expansion and show that the nonlinear theory, called the {\it beyond} \(\delta N\)-formalism for a general single scalar field as the next-leading order in the expansion. Both the leading-order in the expansion (\(\delta N\)-formalism) and our nonlinear theory include the solutions of full-nonlinear orders in the standard perturbative expansion. Additionally, in our formalism, we can deal with the time evolution in contrast to \(\delta N\)-formalism, where curvature perturbations remain just constant, and show decaying modes do not couple with growing modes as similar to the case with linear theory. We can conclude that although the decaying mode diverges when \(\dot{\phi}\) vanishes, there appears no trouble for both the linear and nonlinear theory since these modes will vanish at late times.

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          Nonlinear evolution of long-wavelength metric fluctuations in inflationary models

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            The inflationary prediction for primordial non-gaussianity

            We extend the \delta N formalism so that it gives all of the stochastic properties of the primordial curvature perturbation \zeta if the initial field perturbations are gaussian. The calculation requires only the knowledge of some family of unperturbed universes. A formula is given for the normalisation \fnl of the bispectrum of \zeta, which is the main signal of non-gaussianity. Examples of the use of the formula are given, and its relation to cosmological perturbation theory is explained.
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              Inflation without Slow Roll

              We draw attention to the possibility that inflation (i.e. accelerated expansion) might continue after the end of slow roll, during a period of fast oscillations of the inflaton field \phi . This phenomenon takes place when a mild non-convexity inequality is satisfied by the potential V(\phi). The presence of such a period of \phi-oscillation-driven inflation can substantially modify reheating scenarios. In some models the effect of these fast oscillations might be imprinted on the primordial perturbation spectrum at cosmological scales.
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                Author and article information

                Journal
                20 November 2010
                2010-12-06
                Article
                10.1103/PhysRevD.83.043504
                1011.4566
                7d0a368d-2fcb-43f1-a0ae-62d0fc687d5b

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                History
                Custom metadata
                Phys.Rev.D83:043504,2011
                6 pages, added references
                astro-ph.CO gr-qc hep-th

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