Strongly Coupled Perturbations in Two-Field Inflationary Models

Abstract

We study models of inflation with two scalar fields and non-canonical kinetic terms, focusing on the case in which the curvature and isocurvature perturbations are strongly coupled to each other. In the regime where a heavy mode can be identified and integrated out, we clarify the passage from the full two-field model to an effectively single-field description. However, the strong coupling sets a new scale in the system, and affects the evolution of the perturbations as well as the beginning of the regime of validity of the effective field theory. In particular, the predictions of the model are sensitive to the relative hierarchy between the coupling and the mass of the heavy mode. As a result, observables are not given unambiguously in terms of the parameters of an effectively single field model with non-trivial sound speed. Finally, the requirement that the sound horizon crossing occurs within the regime of validity of the effective theory leads to a lower bound on the sound speed. Our analysis is done in an extremely simple toy model of slow-roll inflation, which is chosen for its tractability, but is non-trivial enough to illustrate the richness of the dynamics in non-canonical multi-field models.

36 pages, 7 figures, v2: references added

References in corpus (14)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Three Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis
• Monodromy in the CMB: Gravity Waves and String Inflation
• Flux Compactification
• String Cosmology: A Review
• Primordial perturbations and non-Gaussianities in DBI and general multi-field inflation
• Perturbations in generalized multi-field inflation
• Curvature and isocurvature perturbations in two-field inflation
• Primordial fluctuations and non-Gaussianities in multi-field DBI inflation
• Mass hierarchies and non-decoupling in multi-scalar field dynamics
• Curvature and isocurvature perturbations from two-field inflation in a slow-roll expansion
• Roulette Inflation with Kähler Moduli and their Axions
• Primordial Non-Gaussianities of General Multiple Field Inflation
• Nonlinear perturbations of cosmological scalar fields with non-standard kinetic terms

Cited by in corpus (1)

• Mass hierarchies and non-decoupling in multi-scalar field dynamics