A nonperturbative light-front coupled-cluster method

TL;DR

This paper introduces a nonperturbative light-front coupled-cluster method for solving quantum field theory bound states, avoiding Fock-space truncation by using an exponential operator approach with nonlinear integral equations.

Contribution

It develops a novel nonperturbative framework combining light-front coordinates with coupled-cluster techniques, enabling accurate bound state calculations without Fock-space truncation.

Findings

Eliminates the need for Fock-space truncation in bound state calculations.

Uses nonlinear integral equations to determine the exponential operator.

Allows calculation of matrix elements, form factors, and observables.

Abstract

The nonperturbative Hamiltonian eigenvalue problem for bound states of a quantum field theory is formulated in terms of Dirac's light-front coordinates and then approximated by the exponential-operator technique of the many-body coupled-cluster method. This approximation eliminates any need for the usual approximation of Fock-space truncation. Instead, the exponentiated operator is truncated, and the terms retained are determined by a set of nonlinear integral equations. These equations are solved simultaneously with an effective eigenvalue problem in the valence sector, where the number of constituents is small. Matrix elements can be calculated, with extensions of techniques from standard coupled-cluster theory, to obtain form factors and other observables.