Application of the light-front coupled-cluster method to $\phi^4$ theory in two dimensions

TL;DR

This paper applies the light-front coupled-cluster method to two-dimensional $^4$ theory, demonstrating a non-truncating approach that yields nonlinear equations for eigenstates, and compares it with traditional Fock-space truncation results.

Contribution

It introduces the LFCC method for $^4$ theory, avoiding Fock-space truncation and providing a new way to compute eigenstates in light-front quantization.

Findings

LFCC method produces nonlinear equations for eigenstates.

Results are comparable to Fock-space truncation with the same number of equations.

Demonstrates the feasibility of LFCC in a quantum field theory setting.

Abstract

As a first numerical application of the light-front coupled-cluster (LFCC) method, we consider the odd-parity massive eigenstate of $\phi_{1+1}^4$ theory. The eigenstate is built as a Fock-state expansion in light-front quantization, where wave functions appear as coefficients of the Fock states. A standard Fock-space truncation would then yield a finite set of linear equations for a finite number of wave functions. The LFCC method replaces Fock-space truncation with a more sophisticated truncation, one which reduces the eigenvalue problem to a finite set of nonlinear equations without any restriction on Fock space. We compare our results with those obtained with a Fock-space truncation that yields the same number of equations.