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Inhomogeneous initial data and small-field inflation

Accepted version
Peer-reviewed

Type

Article

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Authors

Marsh, MCD 
Barrow, JD 
Ganguly, C 

Abstract

We consider the robustness of small-field inflation in the presence of scalar field inhomo- geneities. Previous numerical work has shown that if the scalar potential is flat only over a narrow in- terval, such as in commonly considered inflection-point models, even small-amplitude inhomogeneities present at the would-be onset of inflation at τ = τi can disrupt the accelerated expansion. In this paper, we parametrise and evolve the inhomogeneities from an earlier time τIC at which the initial data were imprinted, and show that for a broad range of inflationary and pre-inflationary models, inflection-point inflation withstands initial inhomogeneities. We consider three classes of perturbative pre-inflationary solutions (corresponding to energetic domination by the scalar field kinetic term, a relativistic fluid, and isotropic negative curvature), and two classes of exact solutions to Einstein’s equations with large inhomogeneities (corresponding to a stiff fluid with cylindrical symmetry, and anisotropic negative curvature). We derive a stability condition that depends on the Hubble scales H(τi) and H(τIC), and a few properties of the pre-inflationary cosmology. For initial data imprinted at the Planck scale, the absence of an inhomogeneous initial data problem for inflection-point inflation leads to a novel, lower limit on the tensor-to-scalar ratio.

Description

Keywords

inflation, initial conditions and eternal universe

Journal Title

Journal of Cosmology and Astroparticle Physics

Conference Name

Journal ISSN

1475-7516
1475-7516

Volume Title

2018

Publisher

IOP Publishing
Sponsorship
Science and Technology Facilities Council (ST/P000673/1)
Science and Technology Facilities Council (ST/L000636/1)
J.D.B. is supported by the Science and Technology Facilities Council (STFC) of the UK. C.G. is supported by the Jawaharlal Nehru Memorial Trust Cambridge International Scholarship. D.M. is supported by a Stephen Hawking Advanced Fellowship at the Centre for Theoretical Cosmology, DAMTP, University of Cambridge.