Quantum modes in DBI inflation: exact solutions and constraints from vacuum selection

Abstract

We study a two-parameter family of exactly solvable inflation models with variable sound speed, and derive a corresponding exact expression for the spectrum of curvature perturbations. We generalize this expression to the slow roll case, and derive an approximate expression for the scalar spectral index valid to second order in slow roll. We apply the result to the case of DBI inflation, and show that for certain choices of slow roll parameters, the Bunch-Davies limit (a) does not exist, or (b) is sensitive to stringy physics in the bulk, which in principle can have observable signatures in the primordial power spectrum.

10 pages, LaTeX; V2: version submitted to PRD. References added, minor error in text corrected

References in corpus (9)

• A Microscopic Limit on Gravitational Waves from D-brane Inflation
• Roulette Inflation with Kähler Moduli and their Axions
• Phenomenology of D-Brane Inflation with General Speed of Sound
• Comparing Infrared Dirac-Born-Infeld Brane Inflation to Observations
• Multifield DBI Inflation and Non-Gaussianities
• Gravitational Wave Constraints on DBI Inflation
• Inflation from Wrapped Branes
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• Reconstructing a general inflationary action
• Stochastic Inflation Revisited: Non-Slow Roll Statistics and DBI Inflation
• Constraints on Kinetically Modified Inflation from WMAP5
• Cosmological constraints on general, single field inflation
• Inflationary potentials in DBI models
• Modification from Noncommutative Inflation