Lorentz-boost eigenmodes

TL;DR

This paper introduces Lorentz-boost eigenmodes, a new set of wave solutions that are eigenmodes of the boost operator, exhibiting unique invariance and scale-invariance properties useful for causal signal propagation.

Contribution

It presents the theoretical formulation and properties of Lorentz-boost eigenmodes, expanding the set of known wave solutions beyond plane and vortex modes.

Findings

Lorentz-boost eigenmodes are invariant under Lorentz boosts along z-axis.

They exhibit scale-invariant waveforms and step-like singularities.

These modes can serve as a basis for analyzing causal signal propagation.

Abstract

Plane waves and cylindrical or spherical vortex modes are important sets of solutions of quantum and classical wave equations. These are eigenmodes of the energy-momentum and angular-momentum operators, i.e., generators of spacetime translations and spatial rotations, respectively. Here we describe another set of wave modes: eigenmodes of the "boost momentum" operator, i.e., a generator of Lorentz boosts (spatio-temporal rotations). Akin to the angular momentum, only one (say, z) component of the boost momentum can have a well-defined quantum number. The boost eigenmodes exhibit invariance with respect to the Lorentz transformations along the z-axis, leading to scale-invariant wave forms and step-like singularities moving with the speed of light. We describe basic properties of the Lorentz-boost eigenmodes and argue that these can serve as a convenient basis for problems involving causal propagation of signals.