Inflation without quantum gravity

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http://hdl.handle.net/10138/310436

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Markkanen , T , Rasanen , S & Wahlman , P 2015 , ' Inflation without quantum gravity ' , Physical Review D : Particles, Fields, Gravitation and Cosmology , vol. 91 , no. 8 , 084064 . https://doi.org/10.1103/PhysRevD.91.084064

Title: Inflation without quantum gravity
Author: Markkanen, Tommi; Rasanen, Syksy; Wahlman, Pyry
Contributor: University of Helsinki, Department of Physics
University of Helsinki, Department of Physics
University of Helsinki, Helsinki Institute of Physics
Date: 2015-04-30
Language: eng
Number of pages: 11
Belongs to series: Physical Review D : Particles, Fields, Gravitation and Cosmology
ISSN: 1550-7998
URI: http://hdl.handle.net/10138/310436
Abstract: It is sometimes argued that observation of tensor modes from inflation would provide the first evidence for quantum gravity. However, in the usual inflationary formalism, also the scalar modes involve quantized metric perturbations. We consider the issue in a semiclassical setup in which only matter is quantized, and spacetime is classical. We assume that the state collapses on a spacelike hypersurface and find that the spectrum of scalar perturbations depends on the hypersurface. For reasonable choices, we can recover the usual inflationary predictions for scalar perturbations in minimally coupled single-field models. In models where nonminimal coupling to gravity is important and the field value is sub-Planckian, we do not get a nearly scale-invariant spectrum of scalar perturbations. As gravitational waves are only produced at second order, the tensor-to-scalar ratio is negligible. We conclude that detection of inflationary gravitational waves would indeed be needed to have observational evidence of quantization of gravity.
Subject: ONE-LOOP CORRECTIONS
COSMOLOGICAL PERTURBATIONS
PRIMORDIAL FLUCTUATIONS
RELATIVISTIC COSMOLOGY
SEMICLASSICAL GRAVITY
SYMMETRY-BREAKING
CHAOTIC INFLATION
UNIVERSE SCENARIO
PHASE-TRANSITION
RELIC GRAVITONS
115 Astronomy, Space science
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