The Linear Regime of Tachyonic Preheating

TL;DR

This paper provides an analytic, model-independent analysis of the linear regime of tachyonic preheating, showing its efficiency, gravitational wave production, and compatibility with observational constraints.

Contribution

It introduces a Floquet theoretic approach to describe mode growth in tachyonic preheating, applicable to various models including larger scalar multiplets.

Findings

Tachyonic preheating is efficient with sub-Planckian field excursions.

It can generate gravitational waves detectable by current and future interferometers.

The process is compatible with observational bounds on tensor-to-scalar ratio.

Abstract

Tachyonic preheating is realized when the inflaton repeatedly returns to a convex region of the potential during the post-inflationary oscillating phase. This will induce a strong tachyonic instability and lead to a rapid fragmentation of the coherent field that can complete within a fraction of an $e$-fold. In this paper, we study the linear regime of this process in a model-independent way. To this purpose, we construct simplified models that provide an analytic Floquet theoretic description of mode growth. This approach captures the essential features of well-motivated tachyonic preheating scenarios, including scenarios in which the inflaton is part of a larger scalar multiplet. We show that tachyonic preheating is efficient if the field excursions are sub-Planckian, can produce gravitational waves in the frequency range of current and future gravitational wave interferometers, and can be consistent with any experimentally allowed tensor-to-scalar ratio.