Staggered Multi-Field Inflation

TL;DR

This paper develops a formalism for staggered multi-field inflation models, showing they produce adiabatic, nearly Gaussian perturbations, and applies it to string theory-inspired scenarios with promising observational agreement.

Contribution

It introduces a new formalism for analyzing staggered multi-field inflation, accommodating time-dependent field numbers and deriving key inflationary observables.

Findings

Isocurvature perturbations are suppressed during inflation.

Models produce nearly Gaussian, adiabatic perturbations.

Applications to string theory scenarios show observational consistency.

Abstract

We investigate multi-field inflationary scenarios with fields that drop out of the model in a staggered fashion. This feature is natural in certain multi-field inflationary setups within string theory; for instance, it can manifest itself when fields are related to tachyons that condense, or inter-brane distances that become meaningless when branes annihilate. Considering a separable potential, and promoting the number of fields to a smooth time-dependent function, we derive the formalism to deal with these models at the background and perturbed level, providing general expressions for the scalar spectral index and the running. We recover known results of e.g. a dynamically relaxing cosmological constant in the appropriate limits. We further show that isocurvature perturbations are suppressed during inflation, so that perturbations are adiabatic and nearly Gaussian. The resulting setup might be interpreted as a novel type of warm inflation, readily implemented within string theory and without many of the shortcomings associated with warm inflation. To exemplify the applicability of the formalism we consider three concrete models: assisted inflation with exponential potentials as a simple toy model (a graceful exit becomes possible), inflation from multiple tachyons (a constant decay rate of the number of fields and negligible slow roll contributions turns out to be in good agreement with observations) and inflation from multiple M5-branes within M-theory (a narrow stacking of branes yields a consistent scenario).