Nonlinear trident in the high-energy limit: Nonlocality, Coulomb field and resummations
Abstract
We study nonlinear trident in laser pulses in the high-energy limit, where the initial electron experiences, in its rest frame, an electromagnetic field strength above Schwinger's critical field. At lower energies the dominant contribution comes from the "two-step" part, but in the high-energy limit the dominant contribution comes instead from the one-step term. We obtain new approximations that explain the relation between the high-energy limit of trident and pair production by a Coulomb field, as well as the role of the Weizs\"acker-Williams approximation and why it does not agree with the high- limit of the locally-constant-field approximation. We also show that the next-to-leading order in the large-a0 expansion is, in the high-energy limit, nonlocal and is numerically very important even for quite large a0. We show that the small-a0 perturbation series has a finite radius of convergence, but using Pad\'e-conformal methods we obtain resummations that go beyond the radius of convergence and have a large numerical overlap with the large-a0 approximation. We use Borel-Pad\'e-conformal methods to resum the small- expansion and obtain a high precision up to very large . We also use newer resummation methods based on hypergeometric/Meijer-G and confluent hypergeometric functions.