From trivial to non-trivial conformal string backgrounds via O(d, d) transformations

Gasperini, M.; Maharana, Jnanadeva; Veneziano, G.

doi:10.1016/0370-2693(91)91831-f

Cited by 108 publications

(99 citation statements)

References 21 publications

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“…the curvature and dilaton have become singular at some fixed proper time. There have been a number of suggested ways to tackle the singularity problem, considering also anisotropic [25,26] and inhomogeneous [27,28] backgrounds, or the presence of a non-local dilaton potential [2]. However, if we confine our attention to homogeneous and isotropic metrics, and to a local potential, one of the most promising approaches to the graceful exit problem [29] suggests that the curvature singularities may be cured by adding higher-order corrections to the string effective action (see for instance [30,31,32,3,4,6]).…”

Section: Introductionmentioning

confidence: 99%

Gravitational waves in non-singular string cosmologies

Cartier¹,

Copeland²,

Gasperini³

2001

Nuclear Physics B

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We study the evolution of tensor metric fluctuations in a class of non-singular models based on the string effective action, by including in the perturbation equation the higher-derivative and loop corrections needed to regularise the background solutions. We discuss the effects of such higher-order corrections on the final graviton spectrum, and we compare the results of analytical and numerical computations. *

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Section: Introductionmentioning

confidence: 99%

Gravitational waves in non-singular string cosmologies

Cartier¹,

Copeland²,

Gasperini³

2001

Nuclear Physics B

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“…[2]). For example, this symmetry has been employed to generate curved backgrounds with a time-dependent tensor potential from flat solutions [10] and homogeneous cosmologies [11]. On the other hand the presence of an SL(2,R) symmetry [12] in the NS-NS sector of the theory can been used to generate a time-dependent field-strength [13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Symmetries for generating string cosmologies

1998

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We discuss the symmetry properties of the low-energy effective action of the type IIB superstring that may be employed to derive four-dimensional solutions. A truncated effective action, compactified on a six-torus, but including both Neveu/Schwarz-Neveu/Schwarz and Ramond-Ramond field strengths, can be expressed as a non-linear sigma model which is invariant under global SL(3,R) transformations. This group contains as a sub-group the SL(2,R) symmetry of the ten-dimensional theory and a discrete Z2 reflection symmetry which leads to a further SL(2,R) sub-group. The symmetries are employed to analyse a general class of spatially homogeneous cosmological solutions with non-trivial Ramond-Ramond fields.

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“…I have included a general dilaton potential, V (φ), and the possible phenomenological contribution of other sources, represented generically by T ν µ . By setting V = 0 and T µν = 0 we find for the system (9.7) the particular exact (anisotropic) solution [7] (with non-trivial torsion H µνα = 0)…”

Section: Possible Origin Of the Cmb Radiationmentioning

confidence: 99%

“…(9.8) Such solution can also be obtained by "inverting" and appropriately "boosting" (through scale factor duality and O(2, 2) transformations) the globally flat metric [7] …”

Section: Possible Origin Of the Cmb Radiationmentioning

confidence: 99%

“…This scenario was originally motivated by the solutions of the string equations of motion in curved backgrounds [4], and by the duality symmetries of the string effective action [5][6][7] (see for instance [8] for a more detailed introduction). Its basic ingredients are an initial weak coupling, perturbative regime characterized by a very small background curvature (in string units), and a final transition to the radiation era controlled by the dilaton dynamics and by the two basic parameters (string length, string coupling) of string theory.…”

Section: Introductionmentioning

confidence: 99%

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Status of String Cosmology: Phenomenological Aspects

Gasperini

1996

String Gravity and Physics at the Planck Energy Scale

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I report recent studies on the evolution of perturbations in the context of the "pre-big-bang" scenario typical of string cosmology, with emphasis on the formation of a stochastic background of relic photons and gravitons, and its possible direct/indirect observable consequences. I also discuss the possible generation of a thermal microwave background by using, as example, a simple gravi-axio-dilaton model whose classical evolution connects smoothly inflationary expansion to decelerated contraction. By including the quantum back-reaction of the produced radiation the model eventually approaches the standard radiation-dominated (constant dilaton) regime.* Lecture given at the 4th Course of the International School of Astrophysics "D. Chalonge" on String gravity and physics at the Planck scale

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From trivial to non-trivial conformal string backgrounds via O(d, d) transformations

Cited by 108 publications

References 21 publications

Gravitational waves in non-singular string cosmologies

Gravitational waves in non-singular string cosmologies

Symmetries for generating string cosmologies

Status of String Cosmology: Phenomenological Aspects

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