Instant Preheating

TL;DR

This paper introduces instant preheating, a nonperturbative and nearly instantaneous reheating mechanism that activates when the inflaton-driven mass $m_ ext{χ}=g|oldsymbol{φ}|$ becomes nonadiabatic near $oldsymbol{φ}=0$. χ particles produced in a narrow window fatten as φ grows and decay to fermions ψ, enabling the production of superheavy states with masses up to $m_ ext{ψ} oughly 10^{17}-10^{18}$ GeV, often far beyond the reach of resonance-based preheating. The authors derive the χ-number density $n_ ext{χ} o (g|oldsymbol{ẋ_0}|)^{3/2}/(8\pi^3)$ and discuss conditions under which the decay chain φ→χ→ψ efficiently reheats the universe within a single oscillation, including in quintessence-like potentials where oscillations are absent. This mechanism broadens the landscape of reheating, enabling GUT-scale baryogenesis and potential dark-matter or black-hole scenarios, and connects to string-inspired contexts where nonadiabatic mass changes are natural.

Abstract

We describe a new efficient mechanism of reheating. Immediately after rolling down the rapidly moving inflaton field $φ$ produces particles $χ$, which may be either bosons or fermions. This is a nonperturbative process which occurs almost instantly; no oscillations or parametric resonance is required. The effective masses of the $χ$ particles may be very small at the moment when they are produced, but they ``fatten'' when the field $φ$ increases. When the particles $χ$ become sufficiently heavy, they rapidly decay to other, lighter particles. This leads to an almost instantaneous reheating accompanied by the production of particles with masses which may be as large as $10^{17}-10^{18}$ GeV. This mechanism works in the usual inflationary models where $V(φ)$ has a minimum, where it takes only a half of a single oscillation of the inflaton field $φ$, but it is especially efficient in models with effective potentials slowly decreasing at large $φ$ as in the theory of quintessence.