Composite Vector Particles in External Electromagnetic Fields

TL;DR

This paper develops an effective field theory for spin-1 particles in external electromagnetic fields, enabling the extraction of electromagnetic properties like charge radii and quadrupole moments from lattice QCD data, especially for the deuteron.

Contribution

It introduces a new effective field theory framework for vector mesons and spin-1 nuclei, facilitating the matching of lattice QCD calculations to physical electromagnetic properties.

Findings

Derived explicit Green's functions in a linearly varying electric field.

Provided formulas to extract charge radius and quadrupole moment from lattice data.

Discussed the feasibility of measuring deuteron properties via lattice QCD.

Abstract

Lattice quantum chromodynamics (QCD) studies of electromagnetic properties of hadrons and light nuclei, such as magnetic moments and polarizabilities, have proven successful with the use of background field methods. With an implementation of nonuniform background electromagnetic fields, properties such as charge radii and higher electromagnetic multipole moments (for states of higher spin) can be additionally obtained. This can be achieved by matching lattice QCD calculations to a corresponding low-energy effective theory that describes the static and quasi-static response of hadrons and nuclei to weak external fields. With particular interest in the case of vector mesons and spin-1 nuclei such as the deuteron, we present an effective field theory of spin-1 particles coupled to external electromagnetic fields. To constrain the charge radius and the electric quadrupole moment of the composite spin-1 field, the single-particle Green's functions in a linearly varying electric field in space are obtained within the effective theory, providing explicit expressions that can be used to match directly onto lattice QCD correlation functions. The viability of an extraction of the charge radius and the electric quadrupole moment of the deuteron from the upcoming lattice QCD calculations of this nucleus is discussed.