Regular cosmological bouncing solutions in low energy effective action from string theories

Fabris, J. C.; Furtado, R. G.; Peter, Patrick; Pinto-Neto, Nelson

doi:10.1103/physrevd.67.124003

Cited by 44 publications

(52 citation statements)

References 30 publications

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“…The features we have discussed can be seen in figure 6, which shows a numerical solution to the combined gravitational equations of motion (6), (8) and the strongcoupling Boltzmann equations (31), (32). The matter energy E has plateaus which 11 Note that no real temperature is dropping here since during the Hagedorn phase the temperature is constant at T H .…”

Section: Shrinking Cyclesmentioning

confidence: 92%

“…Our work provides a simple string-inspired mechanism for obtaining bouncing and cyclic cosmologies. For other studies in this direction see [8,9,10].…”

Section: Bouncing and Cyclic Cosmologiesmentioning

confidence: 99%

“…We have denoted this E max because it's equal to the maximum matter energy during a cycle. To see this recall that the Friedmann equation (8) states that the energy in matter is…”

Section: Shrinking Cyclesmentioning

confidence: 99%

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Bouncing and cyclic string gas cosmologies

2009

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We show that, in the presence of a string gas, simple higher-derivative modifications to the effective action for gravity can lead to bouncing and cyclic cosmological models. The modifications bound the expansion rate and avoid singularities at finite times. In these models the scale factors can have long loitering phases that solve the horizon problem. Adding a potential for the dilaton gives a simple realization of the pre-big bang scenario. Entropy production in the cyclic phase drives an eventual transition to a radiation-dominated universe. As a test of the Brandenberger-Vafa scenario, we comment on the probability of decompactifying three spatial dimensions in this class of models.

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Section: Shrinking Cyclesmentioning

confidence: 92%

“…Our work provides a simple string-inspired mechanism for obtaining bouncing and cyclic cosmologies. For other studies in this direction see [8,9,10].…”

Section: Bouncing and Cyclic Cosmologiesmentioning

confidence: 99%

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Bouncing and cyclic string gas cosmologies

2009

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“…However, particular cases can be explicitly solved. The solutions without the moduli fields were found in reference [15]; the main scenarios for this case will be reviewed below. The equations, in the presence of moduli fields, but in the absence of the Ramond-Ramond (RR) term, will be solved for two main cases: in the absence of the axion field, and in the presence of the axion field.…”

Section: Regular Cosmological Solutionsmentioning

confidence: 99%

“…This means that in the Einstein frame, negative energies are present. The flat solutions of interest were obtained in reference [15]. They are the following:…”

Section: Solutions In Absence Of the Moduli Fieldsmentioning

confidence: 99%

Falsifying tree level string motivated bouncing cosmologies

et al. 2006

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The string effective action at tree level contains, in its bosonic sector, the Einstein-Hilbert term, the dilaton, and the axion, besides scalar and gauge fields coming from the Ramond-Ramond sector. The reduction to four dimensions brings to scene moduli fields. We generalize this effective action by introducing two arbitrary parameters, ω and m, connected with the dilaton and axion couplings. In this way, more general frameworks can be analyzed. Regular solutions with a bounce can be obtained for a range of (negative) values of the parameter ω which, however, exclude the pure string configuration (ω = −1). We study the evolution of scalar perturbations in such cosmological scenarios. The predicted primordial power spectrum decreases with the wavenumber with spectral index ns = −2, in contradiction with the results of the W M AP . Hence, all such effective string motivated cosmological bouncing models seem to be ruled out, at least at the tree level approximation.

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Scalar field as an intrinsic time measure in coupled dynamical matter-geometry systems. I. Neutral gravitational collapse

Nakonieczna

Yeom

2016

J. High Energ. Phys.

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There does not exist a notion of time which could be transferred straightforwardly from classical to quantum gravity. For this reason, a method of time quantification which would be appropriate for gravity quantization is being sought. One of the existing proposals is using the evolving matter as an intrinsic 'clock' while investigating the dynamics of gravitational systems. The objective of our research was to check whether scalar fields can serve as time variables during a dynamical evolution of a coupled multicomponent matter-geometry system. We concentrated on a neutral case, which means that the elaborated system was not charged electrically nor magnetically. For this purpose, we investigated a gravitational collapse of a self-interacting complex and real scalar fields in the Brans-Dicke theory using the 2+2 spacetime foliation. We focused mainly on the region of high curvature appearing nearby the emerging singularity, which is essential from the perspective of quantum gravity. We investigated several formulations of the theory for various values of the Brans-Dicke coupling constant and the coupling between the Brans-Dicke field and the matter sector of the theory. The obtained results indicated that the evolving scalar fields can be treated as time variables in close proximity of the singularity due to the following reasons. The constancy hypersurfaces of the Brans-Dicke field are spacelike in the vicinity of the singularity apart from the case, in which the equation of motion of the field reduces to the wave equation due to a specific choice of free evolution parameters. The hypersurfaces of constant complex and real scalar fields are spacelike in the regions nearby the singularities formed during the examined process. The values of the field functions change monotonically in the areas, in which the constancy hypersurfaces are spacelike.

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Regular cosmological bouncing solutions in low energy effective action from string theories

Cited by 44 publications

References 30 publications

Bouncing and cyclic string gas cosmologies

Bouncing and cyclic string gas cosmologies

Falsifying tree level string motivated bouncing cosmologies

Scalar field as an intrinsic time measure in coupled dynamical matter-geometry systems. I. Neutral gravitational collapse

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