Improvement on cosmological chaotic inflation through nonminimal coupling

Journal Article · Thu Mar 15 04:00:00 EST 1990 · Physical Review, D (Particles Fields); (USA)

DOI:https://doi.org/10.1103/PhysRevD.41.1783· OSTI ID:7003363

Fakir, R; Unruh, W G ^[1]

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1. Canadian Institute for Advanced Research, Cosmology Program, University of British Columbiam, Vancouver (CA) Department of Physics, University of British Columbia, Vancouver, BC (CA)

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.

• OSTI ID: 7003363
• Journal Information: Physical Review, D (Particles Fields); (USA), Journal Name: Physical Review, D (Particles Fields); (USA) Vol. 41:6; ISSN PRVDA; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

640106* -- Astrophysics & Cosmology-- Cosmology
645400 -- High Energy Physics-- Field Theory
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CONSTRAINTS
COSMOLOGICAL MODELS
COSMOLOGY
COUPLING
FIELD THEORIES
GRAVITATIONAL FIELDS
INFLATIONARY UNIVERSE
MATHEMATICAL MODELS
PERTURBATION THEORY
PHASE TRANSFORMATIONS
POTENTIALS
QUANTUM FIELD THEORY
SCALAR FIELDS
SPACE-TIME