Gravitational Wave Constraints on DBI Inflation

Abstract

An upper bound on the amplitude of the primordial gravitational wave spectrum generated during ultra-violet DBI inflation is derived. The bound is insensitive to the form of the inflaton potential and the warp factor of the compactified dimensions and can be expressed entirely in terms of observational parameters once the volume of the five-dimensional sub-manifold of the throat has been specified. For standard type IIB compactification schemes, the bound predicts undetectably small tensor perturbations with a tensor-scalar ratio $r<10^{-7}$. This is incompatible with a corresponding lower limit of $r>0.1(1-n_s)$, which applies to any model that generates a red spectral index $n_s<1$ and a potentially detectable non-Gaussianity in the curvature perturbation. Possible ways of evading these bounds in more general DBI-type scenarios are discussed and a multiple-brane model is investigated as a specific example.

18 pages; V2: added references, version as published in JCAP

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• Spinflation
• Comparing Infrared Dirac-Born-Infeld Brane Inflation to Observations
• Multifield DBI Inflation and Non-Gaussianities
• Inflation in Entropic Cosmology: Primordial Perturbations and non-Gaussianities
• DBI Realizations of the Pseudo-Conformal Universe and Galilean Genesis Scenarios
• Inflation from Wrapped Branes
• On the full quantum trispectrum in multi-field DBI inflation
• Quantum modes in DBI inflation: exact solutions and constraints from vacuum selection
• Warm DBI Inflation
• Lorentz boost and non-Gaussianity in multi-field DBI-inflation
• Generalised DBI-Quintessence
• Non-Gaussianity in single field models without slow-roll
• Non-canonical generalizations of slow-roll inflation models
• Gravitational quantum effects on power spectra and spectral indices with higher-order corrections
• Large Gravitational Waves and Lyth Bound in Multi Brane Inflation
• DBI N-flation
• Quintessence and phantom dark energy from ghost D-branes
• Detectable primordial non-gaussianities and gravitational waves in k-inflation
• Gravitational Wave Constraints on Multi-Brane Inflation
• Warped Wilson Line DBI Inflation
• DBI Inflation in N=1 Supergravity
• Enhanced Inflation in the Dirac-Born-Infeld framework
• Inflation in DBI models with constant gamma
• Dynamics of Dirac-Born-Infeld dark energy interacting with dark matter
• Non-Gaussianities in multi-field DBI inflation with a waterfall phase transition
• Reconstructing Single Field Inflationary Actions From CMBR Data
• Bounds on Tensor wave and Twisted Inflation
• Non-Gaussianities in DBI inflation with angular motion