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Title: Improvement on cosmological chaotic inflation through nonminimal coupling

Abstract

Models of cosmological inflation are plagued with a severe and seemingly unavoidable problem: in order to produce density perturbations of an amplitude consistent with large-scale observations, the self-coupling {lambda} of the {ital inflaton} field has to be tuned to an excessively small value. In all these models, however, the scalar field is taken to be minimally coupled to the scalar curvature ({xi}=0). It is shown here that in the more general case of nonminimal coupling ({xi}{ne}0), and within the framework of Linde's chaotic inflation, the constraint on the self-coupling could be relaxed by several orders of magnitude. We are led to this conclusion by the combination of two key results. (1) Contrary to previous common belief, the curvature coupling {xi} can be almost arbitrarily large without upsetting the inflationary scenario. In fact, the larger {xi} is, the better the model behaves. (2) Considerations regarding the amplitude of density perturbations constrain the {ital ratio} {lambda}/{xi}{sup 2} rather than {lambda}. Thus, by a suitable choice of {xi}, the self-coupling {lambda} can be made as large as desired. It is found that for large {xi} the amplitude of density perturbations is much smaller than in {xi}=0 models: ({delta}{rho}/{rho}){vert bar}{sub {xi}{gt}1}{approx}(48{ital N}{xi}{sup 2}){sup {minus}1/2}more » ({delta}{rho}/{rho}){vert bar}{sub {xi}=0}, where {ital N}{approx}70. For example, this represents a drop of over 4 orders of magnitude for {xi}=10{sup 3}. This same value results in a dramatic 9 orders of magnitude weakening of the constraint on {lambda} according to our formula {lambda}{sub constraint}{vert bar}{sub {xi}{gt}1} {approx}48{ital N}{xi}{sup 2}{lambda}{sub constraint}{vert bar}{sub {xi}=0}. Nonminimal coupling may thus provide a relatively simple solution to the long-standing problem of excessive density perturbations in inflationary models.« less

Authors:
;  [1]
  1. Canadian Institute for Advanced Research, Cosmology Program, University of British Columbiam, Vancouver (CA) Department of Physics, University of British Columbia, Vancouver, BC (CA)
Publication Date:
OSTI Identifier:
7003363
Resource Type:
Journal Article
Journal Name:
Physical Review, D (Particles Fields); (USA)
Additional Journal Information:
Journal Volume: 41:6; Journal ID: ISSN 0556-2821
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; INFLATIONARY UNIVERSE; SCALAR FIELDS; CONSTRAINTS; COSMOLOGY; COUPLING; GRAVITATIONAL FIELDS; PERTURBATION THEORY; PHASE TRANSFORMATIONS; POTENTIALS; QUANTUM FIELD THEORY; SPACE-TIME; COSMOLOGICAL MODELS; FIELD THEORIES; MATHEMATICAL MODELS; 640106* - Astrophysics & Cosmology- Cosmology; 645400 - High Energy Physics- Field Theory

Citation Formats

Fakir, R, and Unruh, W G. Improvement on cosmological chaotic inflation through nonminimal coupling. United States: N. p., 1990. Web. doi:10.1103/PhysRevD.41.1783.
Fakir, R, & Unruh, W G. Improvement on cosmological chaotic inflation through nonminimal coupling. United States. https://doi.org/10.1103/PhysRevD.41.1783
Fakir, R, and Unruh, W G. 1990. "Improvement on cosmological chaotic inflation through nonminimal coupling". United States. https://doi.org/10.1103/PhysRevD.41.1783.
@article{osti_7003363,
title = {Improvement on cosmological chaotic inflation through nonminimal coupling},
author = {Fakir, R and Unruh, W G},
abstractNote = {Models of cosmological inflation are plagued with a severe and seemingly unavoidable problem: in order to produce density perturbations of an amplitude consistent with large-scale observations, the self-coupling {lambda} of the {ital inflaton} field has to be tuned to an excessively small value. In all these models, however, the scalar field is taken to be minimally coupled to the scalar curvature ({xi}=0). It is shown here that in the more general case of nonminimal coupling ({xi}{ne}0), and within the framework of Linde's chaotic inflation, the constraint on the self-coupling could be relaxed by several orders of magnitude. We are led to this conclusion by the combination of two key results. (1) Contrary to previous common belief, the curvature coupling {xi} can be almost arbitrarily large without upsetting the inflationary scenario. In fact, the larger {xi} is, the better the model behaves. (2) Considerations regarding the amplitude of density perturbations constrain the {ital ratio} {lambda}/{xi}{sup 2} rather than {lambda}. Thus, by a suitable choice of {xi}, the self-coupling {lambda} can be made as large as desired. It is found that for large {xi} the amplitude of density perturbations is much smaller than in {xi}=0 models: ({delta}{rho}/{rho}){vert bar}{sub {xi}{gt}1}{approx}(48{ital N}{xi}{sup 2}){sup {minus}1/2} ({delta}{rho}/{rho}){vert bar}{sub {xi}=0}, where {ital N}{approx}70. For example, this represents a drop of over 4 orders of magnitude for {xi}=10{sup 3}. This same value results in a dramatic 9 orders of magnitude weakening of the constraint on {lambda} according to our formula {lambda}{sub constraint}{vert bar}{sub {xi}{gt}1} {approx}48{ital N}{xi}{sup 2}{lambda}{sub constraint}{vert bar}{sub {xi}=0}. Nonminimal coupling may thus provide a relatively simple solution to the long-standing problem of excessive density perturbations in inflationary models.},
doi = {10.1103/PhysRevD.41.1783},
url = {https://www.osti.gov/biblio/7003363}, journal = {Physical Review, D (Particles Fields); (USA)},
issn = {0556-2821},
number = ,
volume = 41:6,
place = {United States},
year = {1990},
month = {3}
}