Localization properties and causality aspects of massless and massive scalar particles

TL;DR

This paper examines the localization and causality issues of massless and massive scalar particles, highlighting the limitations of single-particle localization and advocating for quantum field theoretical approaches.

Contribution

It provides explicit examples illustrating the problems with relativistic particle localization and emphasizes the need for quantum field theory concepts.

Findings

Localization conflicts with causality in relativistic particles

Single particle position operators often violate Minkowski causality

Quantum field theory offers a consistent localization framework

Abstract

Localization properties of scalar single particle states are analyzed by explicit calculational examples with a focus on the massless case. Problems arising from the non-existence of relativistic particle position operators respecting the causal structure of Minkowski spacetime are illustrated by exploring the conflicts arising from localization and causal properties commonly imposed on single particle states. These topics necessitate the introduction of quantum field theoretical localization concepts and are scarcely discussed and often misinterpreted in the literature.