On the Higher Loop Euler-Heisenberg Trans-Series Structure

TL;DR

This paper reveals that the non-perturbative trans-series structure of the Euler-Heisenberg effective Lagrangian in QED changes significantly at two-loop order, with implications for calculations in strong fields.

Contribution

It demonstrates the altered trans-series structure at higher loops and introduces a new approach for computations beyond one-loop order.

Findings

Non-perturbative structure changes at two-loop order.

Branch points replace simple poles in Borel transform.

Accurate extrapolations from weak to strong fields.

Abstract

We show that the one-loop Euler-Heisenberg QED effective Lagrangian in a constant background field acquires a very different non-perturbative trans-series structure at two-loop and higher-loop order in the fine structure constant. Beyond one-loop, virtual particles interact, causing fluctuations about the instantons, whereby the simple poles of the one-loop Borel transform become branch points. We illustrate this in detail at two-loop order using Ritus's seminal result for the renormalized two-loop effective Lagrangian as an exact double-integral representation, and propose a possible new approach to computations at higher loop order. Our methods yield remarkably accurate extrapolations from weak-field to strong-field, and from magnetic to electric background field, at both one-loop and two-loop order, based on surprisingly little perturbative input.