Inflationary nonsingular quantum cosmological model

Falciano, F. T.; Pinto-Neto, Nelson; Santini, E. Sergio

doi:10.1103/physrevd.76.083521

Cited by 36 publications

(47 citation statements)

References 52 publications

(51 reference statements)

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“…an expansion lasting forever, or different phases including contractions and expansions, and therefore bounces. The first situation is realised in the pre-big-bang (PBB) scenario [23,24]; it requires a long accelerated phase originating from either an asymptotically zero volume flat spacetime or from a finite but small compact region [25,26] before the usual decelerated expansion of the standard model. As for bouncing models, they can be embedded in many theoretical situations [27,28,29,30,31,32,33,34,35,36,37,38,39], including classically singular cases [40,41,42].…”

Section: Introductionmentioning

confidence: 99%

Cosmology without inflation

2008

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We propose a new cosmological paradigm in which our observed expanding phase is originated from an initially large contracting Universe that subsequently experienced a bounce. This category of models, being geodesically complete, is non-singular and horizon-free, and can be made to prevent any relevant scale to ever have been smaller than the Planck length. In this scenario, one can find new ways to solve the standard cosmological puzzles. One can also obtain scale invariant spectra for both scalar and tensor perturbations: this will be the case, for instance, if the contracting Universe is dust-dominated at the time at which large wavelength perturbations get larger than the curvature scale. We present a particular example based on a dust fluid classically contracting model, where a bounce occurs due to quantum effects, in which these features are explicit.

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Section: Introductionmentioning

confidence: 99%

Cosmology without inflation

2008

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“…One possible way of circumventing this difficulty seems to be to model the regular component as a perfect fluid. In particular, a suitably small speed of sound for the scalar perturbations ensures that the tensor-to-scalar ratio r is small enough to be consistent with the data [61,62]. Due to the small speed of sound, the scalar perturbations leave the Hubble radius at earlier times (when compared with the tensor perturbations) providing them with more time for their amplitude to grow as the bounce is approached.…”

Section: Introductionmentioning

confidence: 68%

Viable tensor-to-scalar ratio in a symmetric matter bounce

Raveendran

Chowdhury

Sriramkumar

2018

J. Cosmol. Astropart. Phys.

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Abstract. Matter bounces refer to scenarios wherein the universe contracts at early times as in a matter dominated epoch until the scale factor reaches a minimum, after which it starts expanding. While such scenarios are known to lead to scale invariant spectra of primordial perturbations after the bounce, the challenge has been to construct completely symmetric bounces that lead to a tensor-to-scalar ratio which is small enough to be consistent with the recent cosmological data. In this work, we construct a model involving two scalar fields (a canonical field and a non-canonical ghost field) to drive the symmetric matter bounce and study the evolution of the scalar perturbations in the model. We find that the model can be completely described in terms of a single parameter, viz. the ratio of the scale associated with the bounce to the value of the scale factor at the bounce. We evolve the scalar perturbations numerically across the bounce and evaluate the scalar power spectra after the bounce. We show that, while the scalar and tensor perturbation spectra are scale invariant over scales of cosmological interest, the tensor-to-scalar ratio proves to be much smaller than the current upper bound from the observations of the cosmic microwave background anisotropies by the Planck mission. We also support our numerical analysis with analytical arguments.

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“…The specific dependence of the bounce density on the moments agrees with results obtained in the context of the effective Friedmann Eq. (15), where the energy density Q ¼ þ 0 crit þ Á Á Á , according to [37,38], has the leading correction given by 0 ¼ ÁG J " J À ÁG VV . There is a bounce when Q ¼ crit , at which the density is ¼ crit ð1 À 0 Þ.…”

Section: A Zero Potentialmentioning

confidence: 99%

High-density regime of kinetic-dominated loop quantum cosmology

et al. 2010

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We study the dynamics of states perturbatively expanded about a harmonic system of loop quantum cosmology, exhibiting a bounce. In particular, the evolution equations for the first and second-order moments of the system are analyzed. These moments back-react on the trajectories of the expectation values of the state and hence alter the energy density at the bounce. This analysis is performed for isotropic loop quantum cosmology coupled to a scalar field with a small but nonzero constant potential, hence in a regime in which the kinetic energy of matter dominates. Analytic restrictions on the existence of dynamical coherent states and the meaning of semiclassicality within these systems are discussed. A numerical investigation of the trajectories of states that remain semiclassical across the bounce demonstrates that, at least for such states, the bounce persists and that its properties are similar to the standard case, in which the moments of the states are entirely neglected. However, the bounce density does change, implying that a quantum bounce may not be guaranteed to happen when the potential is no longer negligible.

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Inflationary nonsingular quantum cosmological model

Cited by 36 publications

References 52 publications

Cosmology without inflation

Cosmology without inflation

Viable tensor-to-scalar ratio in a symmetric matter bounce

High-density regime of kinetic-dominated loop quantum cosmology

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