Preheating after Multifield Inflation with Nonminimal Couplings, I: Covariant Formalism and Attractor Behavior

TL;DR

This paper develops a covariant formalism to analyze preheating in multifield inflation models with nonminimal couplings, demonstrating persistent single-field attractor behavior that enables efficient energy transfer and avoids de-phasing.

Contribution

It introduces a doubly-covariant formalism for preheating in nonminimally coupled multifield inflation, highlighting features from the field-space manifold and attractor dynamics.

Findings

Single-field attractor behavior persists after inflation.

Preheating avoids de-phasing, enabling efficient energy transfer.

Features depend on nonminimal coupling parameters.

Abstract

This is the first of a three-part series of papers, in which we study the preheating phase for multifield models of inflation involving nonminimal couplings. In this paper, we study the single-field attractor behavior that these models exhibit during inflation and quantify its strength and parameter dependence. We further demonstrate that the strong single-field attractor behavior persists after the end of inflation. Preheating in such models therefore generically avoids the "de-phasing" that typically affects multifield models with minimally coupled fields, allowing efficient transfer of energy from the oscillating inflaton condensate(s) to coupled perturbations across large portions of parameter space. We develop a doubly-covariant formalism for studying the preheating phase in such models and identify several features specific to multifield models with nonminimal couplings, including effects that arise from the nontrivial field-space manifold. In papers II and III, we apply this formalism to study how the amplification of adiabatic and isocurvature perturbations varies with parameters, highlighting several distinct regimes depending on the magnitude of the nonminimal couplings $\xi_I$.