Electromagnetic Properties for Arbitrary Spin Particles: Part 1 $-$ Electromagnetic Current and Multipole Decomposition

TL;DR

This paper develops a comprehensive framework for describing the electromagnetic properties of particles with arbitrary spin, including a decomposition of the current and relations between form factors and moments, laying groundwork for future studies.

Contribution

It introduces a covariant decomposition of the electromagnetic current and defines multipole form factors for arbitrary spin particles, connecting them to electromagnetic moments.

Findings

Derived all natural electromagnetic moments for pointlike particles of any spin.

Established a relation between covariant vertex functions and multipole form factors.

Proposed a transparent decomposition of the electromagnetic current in covariant terms.

Abstract

In a set of two papers, we propose to study an old-standing problem, namely the electromagnetic interaction for particles of arbitrary spin. Based on the assumption that light-cone helicity at tree level and $Q^2=0$ should be conserved non-trivially by the electromagnetic interaction, we are able to derive \emph{all} the natural electromagnetic moments for a pointlike particle of \emph{any} spin. In this first paper, we propose a transparent decomposition of the electromagnetic current in terms of covariant vertex functions. We also define in a general way the electromagnetic multipole form factors, and show their relation with the electromagnetic moments. Finally, by considering the Breit frame, we relate the covariant vertex functions to multipole form factors.