Universality and scaling in multi-field $\alpha$-attractor preheating

TL;DR

This paper analyzes preheating in multi-field $ ext{alpha}$-attractor models with curved field-space, revealing universal scaling laws and demonstrating that preheating efficiency increases with curvature and potential steepness, often becoming instantaneous.

Contribution

It provides analytical tools like WKB and Floquet analysis to estimate preheating efficiency and uncovers universal features and scaling laws in multi-field $ ext{alpha}$-attractor models.

Findings

Preheating speed increases with field-space curvature and potential steepness.

Universal preheating features emerge across different potential steepness values.

Preheating becomes nearly instantaneous at very high field-space curvature.

Abstract

We explore preheating in multi-field models of inflation in which the field-space metric is a highly curved hyperbolic manifold. One broad family of such models is called $\alpha$-attractors, whose single-field regimes have been extensively studied in the context of inflation and supergravity. We focus on a simple two-field generalization of the $T$-model, which has received renewed attention in the literature. Krajewski et al. concluded, using lattice simulations, that multi-field effects can dramatically speed-up preheating. We recover their results and further demonstrate that significant analytical progress can be made for preheating in these models using the WKB approximation and Floquet analysis. We find a simple scaling behavior of the Floquet exponents for large values of the field-space curvature, that enables a quick estimation of the $T$-model reheating efficiency for any large value of the field-space curvature. In this regime we further observe and explain universal preheating features that arise for different values of the potential steepness. In general preheating is faster for larger negative values of the field-space curvature and steeper potentials. For very highly curved field-space manifolds preheating is essentially instantaneous.