scholarly journals Comparison of primordial tensor power spectra from the deformed algebra and dressed metric approaches in loop quantum cosmology

2015 ◽  
Vol 91 (8) ◽  
Author(s):  
Boris Bolliet ◽  
Julien Grain ◽  
Clément Stahl ◽  
Linda Linsefors ◽  
Aurélien Barrau
Keyword(s):  
Quantum Cosmology ◽  
Power Spectra ◽  
Loop Quantum Cosmology ◽  
Tensor Power ◽  
Deformed Algebra

scholarly journals The perturbed universe in the deformed algebra approach of loop quantum cosmology

2016 ◽  
Vol 25 (08) ◽  
pp. 1642003 ◽  
Author(s):  
Julien Grain
Keyword(s):  
Quantum Gravity ◽  
Quantum Cosmology ◽  
Initial Conditions ◽  
Power Spectra ◽  
Quantum Corrections ◽  
Loop Quantum Cosmology ◽  
Algebra Approach ◽  
Deformed Algebra ◽  
Contracting Phase ◽  
The Universe

Loop Quantum Cosmology (LQC) is a tentative approach to model the universe down to the Planck era where quantum gravity settings are needed. The quantization of the universe as a dynamical spacetime is inspired by Loop Quantum Gravity (LQG) ideas. In addition, LQC could bridge contact with astronomical observations, and thus potentially investigate quantum cosmology modelings in the light of observations. To do so however, modeling both the background evolution and its perturbations is needed. The latter described cosmic inhomogeneities that are the main cosmological observables. In this context, we present the so-called deformed algebra approach implementing the quantum corrections to the perturbed universe at an effective level by taking great care of gauge issues. We particularly highlight that in this framework, the algebra of hypersurface deformation receives quantum corrections, and we discuss their meaning. The primordial power spectra of scalar and tensor inhomogeneities are then presented, assuming initial conditions are set in the contracting phase preceding the quantum bounce and the well-known expanding phase of the cosmic history. These spectra are subsequently propagated to angular power spectra of the anisotropies of the cosmic microwave background. It is then shown that regardless of the choice for the initial conditions inside the effective approach for the background evolution (except that they are set in the contracting phase), the predicted angular power spectra of the polarized [Formula: see text]-modes exceed the upper bound currently set by observations. The exclusion of this specific version of LQC establishes the falsifiability of the approach, though one shall not conclude here that either LQC or LQG excluded.

scholarly journals Non-Oscillatory Power Spectrum From States of Low Energy in Kinetically Dominated Early Universes

2021 ◽  
Vol 8 ◽  
Author(s):  
Mercedes Martín-Benito ◽  
Rita B. Neves ◽  
Javier Olmedo
Keyword(s):  
Power Spectrum ◽  
Quantum Cosmology ◽  
Initial Conditions ◽  
Power Spectra ◽  
Low Energy ◽  
Loop Quantum Cosmology ◽  
Test Function ◽  
Vacuum States ◽  
Oscillatory Power ◽  
Definition Of

Recently, States of Low Energy (SLEs) have been proposed as viable vacuum states of primordial perturbations within Loop Quantum Cosmology (LQC). In this work we investigate the effect of the high curvature region of LQC on the definition of SLEs. Shifting the support of the test function that defines them away from this regime results in primordial power spectra of perturbations closer to those of the so-called Non-oscillatory (NO) vacuum, which is another viable choice of initial conditions previously introduced in the LQC context. Furthermore, through a comparison with the Hadamard-like SLEs, we prove that the NO vacuum is of Hadamard type as well.

scholarly journals The Vacuum State of Primordial Fluctuations in Hybrid Loop Quantum Cosmology

Universe ◽  
2018 ◽  
Vol 4 (10) ◽  
pp. 98 ◽  
Author(s):  
Beatriz Elizaga Navascués ◽  
Daniel Martín de Blas ◽  
Guillermo Mena Marugán
Keyword(s):  
General Relativity ◽  
Kinetic Energy ◽  
Quantum Cosmology ◽  
Power Spectra ◽  
Mass Term ◽  
Vacuum State ◽  
Initial Time ◽  
Loop Quantum Cosmology ◽  
Quantum Geometry ◽  
Effective Dynamics

We investigate the role played by the vacuum of the primordial fluctuations in hybrid Loop Quantum Cosmology. We consider scenarios where the inflaton potential is a mass term and the unperturbed quantum geometry is governed by the effective dynamics of Loop Quantum Cosmology. In this situation, the phenomenologically interesting solutions have a preinflationary regime where the kinetic energy of the inflaton dominates over the potential. For these kind of solutions, we show that the primordial power spectra depend strongly on the choice of vacuum. We study in detail the case of adiabatic states of low order and the non-oscillating vacuum introduced by Martín de Blas and Olmedo, all imposed at the bounce. The adiabatic spectra are typically suppressed at large scales, and display rapid oscillations with an increase of power at intermediate scales. In the non-oscillating vacuum, there is power suppression for large scales, but the rapid oscillations are absent. We argue that the oscillations are due to the imposition of initial adiabatic conditions in the region of kinetic dominance, and that they would also be present in General Relativity. Finally, we discuss the sensitivity of our results to changes of the initial time and other data of the model.

scholarly journals A first step towards the inflationary trans-Planckian problem treatment in loop quantum cosmology

2018 ◽  
Vol 27 (07) ◽  
pp. 1850067 ◽  
Author(s):  
Killian Martineau ◽  
Aurélien Barrau ◽  
Julien Grain
Keyword(s):  
Observational Data ◽  
Quantum Cosmology ◽  
Initial Conditions ◽  
Power Spectra ◽  
Dispersion Relations ◽  
Loop Quantum Cosmology ◽  
Modified Dispersion Relations

For most initial conditions, cosmologically relevant physical modes were trans-Planckian at the bounce time, often by many magnitude orders. We improve the usual loop quantum cosmology calculation of the primordial power spectra — in the inflationary framework — by accounting for those trans-Planckian effects through modified dispersion relations. This can induce drastic changes in the spectrum, making it either compatible or incompatible with observational data, depending on the details of the choices operated.

scholarly journals Non-oscillating power spectra in loop quantum cosmology

2020 ◽  
Author(s):  
Beatriz Elizaga Navascués ◽  
Guillermo A Mena Marugan ◽  
Santiago Prado
Keyword(s):  
Quantum Cosmology ◽  
Power Spectra ◽  
Loop Quantum Cosmology

scholarly journals Covariant entropy bound and loop quantum cosmology

2008 ◽  
Vol 78 (6) ◽  
Author(s):  
Abhay Ashtekar ◽  
Edward Wilson-Ewing
Keyword(s):  
Quantum Cosmology ◽  
Loop Quantum Cosmology ◽  
Entropy Bound
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