A unitary and causal effective field theory

TL;DR

This paper introduces a new effective field theory scheme based on the chiral Lagrangian to analyze various pion and nucleon scattering processes, achieving accurate predictions up to 1300 MeV.

Contribution

It develops a unified, causal, and gauge-invariant framework using chiral perturbation theory for analyzing pion-nucleon and related scattering processes.

Findings

Reproduces experimental data up to 1300 MeV

Calculates subthreshold partial-wave amplitudes

Ensures consistency with causality and gauge invariance

Abstract

We report on a novel scheme based on the chiral Lagrangian. It is used to analyze pion-nucleon scattering, pion photoproduction, and nucleon Compton scattering. Subthreshold partial-wave amplitudes are calculated in chiral perturbation theory and analytically extrapolated with constraints imposed by electromagnetic-gauge invariance, causality and unitarity. Experimental quantities are reproduced up to energies $\sqrt{s}\simeq 1300$ MeV in terms of the parameters relevant at order $Q^3$.