Observational Signatures of Gravitational Couplings in DBI Inflation

Abstract

In scalar-tensor theories the scalar fields generically couple nontrivially to gravity. We study the observable properties of inflationary models with non-minimally coupled inflaton and Dirac-Born-Infeld (DBI) kinetic term. Within the assumptions of the priors of our Monte-Carlo simulations we find these models can generate new interesting observable signatures. Our discussion focuses on string theory inspired phenomenological models of relativistic D-brane inflation. While successful string theory constructions of ultra-violet DBI brane inflation remain elusive, we show that in suitable regions of the parameter space it is possible to use cosmological observables to probe the non-minimial coupling. Fortunately, the most observationally promising range of parameters include models yielding intermediate levels of non-gaussianity in the range consistent with WMAP 5-year data, and to be constrained further by the Planck satellite.

Minor revisions and references added. Version to appear in PRD

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• Inflation driven by scalar field with non-minimal kinetic coupling with Higgs and quadratic potentials
• Gauge invariant cosmological perturbations for the nonminimally coupled inflaton field
• Non-Gaussianities of Single Field Inflation with Non-minimal Coupling
• Initial Conditions for Non-Canonical Inflation
• Inflationary predictions in scalar-tensor DBI inflation
• Optimizing future experimental probes of inflation
• Slow-Roll Inflation with Exponential Potential in Scalar-Tensor Models
• Slow-Roll Inflation in Scalar-Tensor Models
• Can the Big Bang Singularity be avoided by a single scalar field?
• Higgs inflation with non-minimal derivative coupling to gravity
• The Degeneracy Problem in Non-Canonical Inflation
• Spinflation with Angular Potentials
• Embedding DBI inflation in scalar-tensor theory
• Observational consequences of the Standard Model Higgs inflation variants
• Brane Bremsstrahlung in DBI Inflation
• Ruling out an inflation driven by a power law potential: kinetic coupling does not help
• Horizon-preserving dualities and perturbations in non-canonical scalar field cosmologies
• Perturbation Theory in k-Inflation Coupled to Matter
• Trapped Brane Features in DBI Inflation
• Where does curvaton reside? Differences between bulk and brane frames
• Spinflation with backreaction