Quantum Gravity in the Sky: Interplay between fundamental theory and observations

Abstract

Observational missions have provided us with a reliable model of the evolution of the universe starting from the last scattering surface all the way to future infinity. Furthermore given a specific model of inflation, using quantum field theory on curved space-times this history can be pushed \emph{back in time} to the epoch when space-time curvature was some $10^{62}$ times that at the horizon of a solar mass black hole! However, to extend the history further back to the Planck regime requires input from quantum gravity. An important aspect of this input is the choice of the background quantum geometry and of the Heisenberg state of cosmological perturbations thereon, motivated by Planck scale physics. This paper introduces first steps in that direction. Specifically we propose two principles that link quantum geometry and Heisenberg uncertainties in the Planck epoch with late time physics and explore in detail the observational consequences of the initial conditions they select. We find that the predicted temperature-temperature (T-T) correlations for scalar modes are indistinguishable from standard inflation at small angular scales even though the initial conditions are now set in the deep Planck regime. However, \emph{there is a specific power suppression at large angular scales}. As a result, the predicted spectrum provides a better fit to the PLANCK mission data than standard inflation, where the initial conditions are set in the general relativity regime. Thus, our proposal brings out a deep interplay between the ultraviolet and the infrared. Finally, the proposal also leads to specific predictions for power suppression at large angular scales also for the (T-E and E-E) correlations involving electric polarization. The PLANCK team is expected to release this data in the coming year.

Invited article, to appear in CQG. This paper is addressed both to the quantum gravity and cosmology audiences. Cosmologists can focus just on sections I, IV.C, IV.D and V without loss of continuity. 43 pages, 13 figures. Version 2 contains a few clarifications and new references, especially to compare and contrast related results in the literature

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Cited by in corpus (8)

• A Short Review of Loop Quantum Gravity
• Quantum-gravitational effects on gauge-invariant scalar and tensor perturbations during inflation: The slow-roll approximation
• Phenomenological implications of modified loop cosmologies: an overview
• Mass of cosmological perturbations in the hybrid and dressed metric formalisms of Loop Quantum Cosmology for the Starobinsky and exponential potentials
• Measuring the effects of Loop Quantum Cosmology in the CMB data
• Spontaneous collapse models lead to the emergence of classicality of the Universe
• Hartle-Hawking wave function and large-scale power suppression of CMB
• The Effect of a positive cosmological constant on the bounce of Loop Quantum Cosmology