Noninflationary model with scale invariant cosmological perturbations

Peter, Patrick; Pinho, Emanuel J. C.; Pinto-Neto, Nelson

doi:10.1103/physrevd.75.023516

Cited by 99 publications

(131 citation statements)

References 42 publications

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“…This is also consistent with predictions from loop quantum gravity [83,84], where it is shown that the era of accelerated expansion will be followed by an era of contraction. It may be noted that unstable geometries can mathematically decay into bubble of nothing, which contain neither matter nor spacetime [85,86].…”

Section: Deformed Wheeler-dewitt Equationsupporting

confidence: 79%

Discreteness of time in the evolution of the universe

Faizal

Ali

Das

2017

Int. J. Mod. Phys. A

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In this paper, we will first derive the Wheeler-DeWitt equation for the generalized geometry which occurs in M-theory. Then we will observe that M2-branes act as probes for this generalized geometry, and as M2-branes have an extended structure, their extended structure will limits the resolution to which this generalized geometry can be defined. We will demonstrate that this will deform the Wheeler-DeWitt equation for the generalized geometry. We analyse such a deformed Wheeler-DeWitt equation in the minisuperspace approximation, and observe that this deformation can be used as a solution to the problem of time. This is because this deformation gives rise to time crystals in our universe due to the spontaneous breaking of time re-parametrization invariance.

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Section: Deformed Wheeler-dewitt Equationsupporting

confidence: 79%

Discreteness of time in the evolution of the universe

Faizal

Ali

Das

2017

Int. J. Mod. Phys. A

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“…On the other hand, the behavior of quantum fluctuations during this period and their link with the emerging primordial matter power spectrum are complicated issues which deserve more profound investigation. See also [28][29][30].…”

Section: Integration Of the Exactly Solvable Casesmentioning

confidence: 99%

Bouncing solutions in Rastall’s theory with a barotropic fluid

et al. 2013

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Rastall's theory is a modification of Einstein's theory of gravity where the covariant divergence of the stress-energy tensor is no more vanishing, but proportional to the gradient of the Ricci scalar. The motivation of this theory is to investigate a possible non-minimal coupling of the matter fields to geometry which, being proportional to the curvature scalar, may represent an effective description of quantum gravity effects. Non-conservation of the stressenergy tensor, via Bianchi identities, implies new field equations which have been recently used in a cosmological context, leading to some interesting results. In this paper we adopt Rastall's theory to reproduce some features of the effective Friedmann's equation emerging from loop quantum cosmology. We determine a class of bouncing cosmological solutions and comment about the possibility of employing these models as effective descriptions of the full quantum theory. *

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“…In this case, the issue of the wavefunction collapse becomes irrelevant since it just corresponds to a situation where the observer updates its knowledge (in the Bayesian sense) about the physical properties of the system. Other attempts, such as the non-local hidden variable theories, have also been tried [52][53][54][55][56][57]. In all these cases, the cosmological situation does not differ much from a conventional laboratory situation and, moreover, does not lead to new, falsifiable, predictions 1 .…”

Section: Introductionmentioning

confidence: 99%

Cosmological inflation and the quantum measurement problem

2012

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According to cosmological inflation, the inhomogeneities in our universe are of quantum mechanical origin. This scenario is phenomenologically very appealing as it solves the puzzles of the standard hot big bang model and naturally explains why the spectrum of cosmological perturbations is almost scale invariant. It is also an ideal playground to discuss deep questions among which is the quantum measurement problem in a cosmological context. Although the large squeezing of the quantum state of the perturbations and the phenomenon of decoherence explain many aspects of the quantum to classical transition, it remains to understand how a specific outcome can be produced in the early universe, in the absence of any observer. The Continuous Spontaneous Localization (CSL) approach to quantum mechanics attempts to solve the quantum measurement question in a general context. In this framework, the wavefunction collapse is caused by adding new non linear and stochastic terms to the Schrödinger equation. In this paper, we apply this theory to inflation, which amounts to solving the CSL parametric oscillator case. We choose the wavefunction collapse to occur on an eigenstate of the Mukhanov-Sasaki variable and discuss the corresponding modified Schrödinger equation. Then, we compute the power spectrum of the perturbations and show that it acquires a universal shape with two branches, one which remains scale invariant and one with n S = 4, a spectral index in obvious contradiction with the Cosmic Microwave Background (CMB) anisotropy observations. The requirement that the non-scale invariant part be outside the observational window puts stringent constraints on the parameter controlling the deviations from ordinary quantum mechanics. Due to the absence of a CSL amplification mechanism in field theory, this has also for consequence that the collapse mechanism of the inflationary fluctuations is not efficient. Then, we determine the collapse time. On small scales the collapse is almost instantaneous, and we recover exactly the behavior of the CSL harmonic oscillator (a case for which we present new results), whereas, on large scales, we find that the collapse is delayed and can take several e-folds to happen. We conclude that recovering the observational successes of inflation and, at the same time, reaching a satisfactory resolution of the inflationary "macro-objectification" issue seems problematic in the framework considered here. This work also provides a complete solution to the CSL parametric oscillator system, a topic we suggest could play a very important rôle to further constrain the CSL parameters. Our results illustrate the remarkable power of inflation and cosmology to constrain new physics.

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Noninflationary model with scale invariant cosmological perturbations

Cited by 99 publications

References 42 publications

Discreteness of time in the evolution of the universe

Discreteness of time in the evolution of the universe

Bouncing solutions in Rastall’s theory with a barotropic fluid

Cosmological inflation and the quantum measurement problem

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