Symmetries for generating string cosmologies

Copeland, Edmund J.; Lidsey, James E.; Wands, David

doi:10.1103/physrevd.58.043503

Cited by 31 publications

(77 citation statements)

References 65 publications

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“…As an example of a model in which the parameters l, m are non-trivial, we consider a nonlinear sigma model in Einstein gravity where the scalar fields parameterize a SL(3, R)/SO(3) coset [28]. In particular we consider the following lowest order action in 4-D Einstein frame [22] …”

Section: Intermediate String Phasementioning

confidence: 99%

Superhorizon curvaton amplitude in inflation and pre-big bang cosmology

Sloth¹

2003

Nuclear Physics B

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We follow the evolution of the curvaton on superhorizon scales and check that the spectral tilt of the curvaton perturbations is unchanged as the curvaton becomes nonrelativistic. Both inflation and pre-big bang cosmology can be treated since the curvaton mechanism within the two scenarios works the same way. We also discuss the amplitude of the density perturbations, which leads to some interesting constrains on the pre-big bang scenario. It is shown that within a SL(3, R) non-linear sigma model one of the three axions has the right coupling to the dilaton and moduli to yield a flat spectrum with a high string scale, if a quadratic non-perturbative potential is generated and an intermediate string phase lasts long enough.

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Section: Intermediate String Phasementioning

confidence: 99%

Superhorizon curvaton amplitude in inflation and pre-big bang cosmology

Sloth¹

2003

Nuclear Physics B

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“…(10) and the graviton and dilaton spectra on large scales remain invariant under T-duality or S-duality transformations of the background model. However the axion-type fields are minimally coupled in the conformally related axion frames [8,12]. SL(2,Z) Sduality transformations of the power-law vacuum solutions lead to a scale factor in the axion frame which evolves as given in Eq.…”

mentioning

confidence: 99%

“…However an identical spectrum of gravitational waves will be produced by the two parameter family of solutions given in Eq. (12).…”

mentioning

confidence: 99%

Duality invariance of cosmological perturbation spectra

1999

Self Cite

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I show that cosmological perturbation spectra produced from quantum fluctuations in massless or self-interacting scalar fields during an inflationary era remain invariant under a two parameter family of transformations of the homogeneous background fields. This relates slow-roll inflation models to solutions which may be far from the usual slow-roll limit. For example, a scale-invariant spectrum of perturbations in a minimally coupled, massless field can be produced by an exponential expansion with a ∝ e Ht , or by a collapsing universe with a ∝ (−t) 2/3 . to appear in Phys Rev D PACS numbers: 98.80.Cq Preprint PU-RCG/98-15v3, gr-qc/9809062The spectrum of perturbations on large scales is a key test of any models of the early universe. During an inflationary era quantum fluctuations on small scales become stretched beyond the horizon generating inhomogeneities on super-horizon scales that are otherwise inexplicable in the standard big bang model [1][2][3]. Conventional models of slow-roll inflation generally predict an almost scaleinvariant spectrum of adiabatic density perturbations [4]. As major observational programs are now underway to produce detailed maps of these perturbations, it is important to investigate whether one can uniquely reconstruct the inflationary history of the universe from the spectrum of inhomogeneities. This question has received considerable attention in recent years in the context of slow-roll inflation [5] where it has been realised that there is a degeneracy in the spectrum of adiabatic density perturbations. This could be removed by a detection of the gravitational wave background on the same scale which, in the slow-roll approximation, gives a direct record of the evolution of the scale factor, and hence of the inflaton potential.By contrast there has been relatively little study of the reconstruction of the evolution in the non-slow-roll case [6]. Recently it has been discovered that the spectra of perturbations produced in so-called pre-big bang models of the early universe [7], based on solutions of the low energy string effective action, are invariant under SL(2,R) symmetry transformations (including S-duality transformations) of the background fields [8]. This raises the interesting question of what is the most general type of cosmological evolution that yields a given perturbation spectrum.I will consider linear perturbations, δφ(η, x i ), about a homogeneous background, φ(η), in a homogeneous cosmology. For a minimally coupled massless field we can neglect any back-reaction upon the spacetime curvature to first order, and so perturbations obey the wave equationδwhere a dot denotes derivatives with respect to cosmic time t, and 3H corresponds to the expansion rate of the homogeneous hypersurfaces. One can decompose the perturbations into independent wavemodes δφ k (η)Q k (x i ), where Q k (x i ) is the eigenfunction of the spatial Laplacian ∇ 2 with eigenvalue −k 2 . The canonically normalised quantum field corresponds to the conformal field perturbation u = aδφ, where the sc...

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“…Let us begin with the case Q = 0. This case corresponds to the axionic cosmology extended to 10D by the addition of rolling moduli, which has been investigated recently by Copeland, Lidsey and Wands [44]. The equations of motion reduce to…”

Section: Cosmic Branesmentioning

confidence: 99%

“…A more detailed inspection of these equations shows that regardless of the frame, the solutions for the scale factors behave as powers of the comoving time [17,44]. In addition, they are all singular, and hence can still be grouped into different branches, much like when the internal space is constant.…”

Section: String Theory Actions and Equations Of Motionsmentioning

confidence: 99%

Erratum: Cosmological solutions in M and string theory [Phys. Rev. D57, 7340 (1998)]

Kaloper¹,

Kogan²,

Olive³

1999

Phys. Rev. D

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We consider solutions to the cosmological equations of motion in 11 dimensions with and without 4-form charges. We show explicitly the correspondence between some of these solutions and known solutions in 10 dimensional string gravity. New solutions involving combinations of 4-form charges are explored. We also speculate on the possibility of removing curvature singularities present in 10D theories by oxidizing to 11D.

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Symmetries for generating string cosmologies

Cited by 31 publications

References 65 publications

Superhorizon curvaton amplitude in inflation and pre-big bang cosmology

Superhorizon curvaton amplitude in inflation and pre-big bang cosmology

Duality invariance of cosmological perturbation spectra

Erratum: Cosmological solutions in M and string theory [Phys. Rev. D57, 7340 (1998)]

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