A nonsingular universe

Mukhanov, Viatcheslav; Brandenberger, Robert H.

doi:10.1103/physrevlett.68.1969

Cited by 875 publications

(1,669 citation statements)

References 18 publications

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“…This leads at t > 0 to a Bardeen potential with the mild scale dependence given by Eq. (14), and to a curvature perturbation which by the time of radiation domination has the same scale-dependence, which can agree with observation.…”

supporting

confidence: 80%

The failure of cosmological perturbation theory in the new ekpyrotic and cyclic ekpyrotic scenarios

Lyth

2002

Physics Letters B

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supporting

confidence: 80%

The failure of cosmological perturbation theory in the new ekpyrotic and cyclic ekpyrotic scenarios

Lyth

2002

Physics Letters B

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“…In this section we will explicitly write the relevant perturbation equations in the conformal gauge [9,8]. We will consider two fluids, the inflaton field which for simplicity we will treat as non-relativistic matter and radiation.…”

Section: Perturbation Equationsmentioning

confidence: 99%

New mechanism for generating density perturbations from inflation

2004

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We propose a new mechanism to generate density perturbations in inflationary models. Spatial fluctuations in the decay rate of the inflaton field to ordinary matter lead to fluctuations in the reheating temperature. We argue that in most realistic models of inflation the coupling of the inflaton to normal matter is determined by the vacuum expectation values of fields in the theory. If those fields are light during inflation (this is a generic situation in the minimal models of supersymmetric inflation) they will fluctuate leading to density perturbations through the proposed mechanism. We show that these fluctuations could easily dominate over the ones generated through the standard mechanism. The new scenario has several consequences for inflation model building and observations. The proposed mechanism allows to generate the observed level of density perturbations with a much lower scale of inflation and thus generically predicts a smaller level of gravitational waves. The relation between the slope of the spectrum of the produced density perturbations and the potential of the inflaton field is different from the standard relations obtained in the context of slow roll inflation. Because the field responsible for the fluctuations is not the inflaton, it can have significantly larger self couplings and thus density perturbations could be non-Gaussian. The non-Gaussianity can be large enough to be detectable by CMB and Large Scale Structure observations.

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“…Finally, in the more general case where V ∂1∂2V ∂1V ∂2V is approximately constant during inflation, T SS can be approximated by an analytic function similar to equation (82), but possessing additional powers of (V e /V * ). Importantly, all of the above models share the commonality that either M 12 or V ∂1∂2V ∂1V ∂2V is exactly or approximately constant.…”

Section: A Calculation Of Fnl Using the δN Formalismmentioning

confidence: 99%

“…where δφ represents the field perturbation in the flat gauge, which coincides with the gauge-invariant Mukhanov-Sasaki variable [81,82]. (In comparison to [77], we drop the subscript f on δφ f since we are working exclusively in the flat gauge.)…”

Section: Perturbations Transfer Functions and Power Spectramentioning

confidence: 99%

Non-Gaussianity in two-field inflation

2011

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We derive semi-analytic formulae for the local bispectrum and trispectrum in general two-field inflation and provide a simple geometric recipe for building observationally allowed models with observable non-Gaussianity. We use the δN formalism to express the bispectrum in terms of spectral observables and the transfer functions, which encode the super-horizon evolution of modes. Similarly, we calculate the trispectrum and show that the trispectrum parameter τNL can be expressed entirely in terms of spectral observables, which provides a new consistency relation unique to two-field inflation. We show that in order to generate observably large non-Gaussianity during inflation, the sourcing of curvature modes by isocurvature modes must be extremely sensitive to a change in the initial conditions orthogonal to the inflaton trajectory and that the amount of sourcing must be non-zero. Under some minimal assumptions, we argue that the first condition is satisfied only when neighboring trajectories through the two-dimensional field space diverge during inflation. Geometrically, this means that the inflaton must roll along a ridge in the potential V for some time during inflation and that its trajectory must turn somewhat in field space. Therefore, it follows that under our assumptions, two-field scenarios with attractor solutions necessarily produce small nonGaussianity. This explains why it has been so difficult to achieve large non-Gaussianity in two-field inflation, and why it has only been achieved in a narrow class of models where the potential and/or the initial conditions are fine-tuned. Some of our conclusions generalize at least qualitatively to multi-field inflation and to scenarios where the interplay between curvature and isocurvature modes can be represented by the transfer function formalism.

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A nonsingular universe

Cited by 875 publications

References 18 publications

The failure of cosmological perturbation theory in the new ekpyrotic and cyclic ekpyrotic scenarios

The failure of cosmological perturbation theory in the new ekpyrotic and cyclic ekpyrotic scenarios

New mechanism for generating density perturbations from inflation

Non-Gaussianity in two-field inflation

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