Achronal localization and representation of the causal logic from a conserved current, application to the massive scalar boson

TL;DR

This work develops a covariant and causal framework for localizing a massive scalar boson in Minkowski spacetime by introducing achronal localization (AL) built from fluxes of covariant conserved currents through achronal surfaces. It rigorously extends the divergence theorem to open sets with almost Lipschitz boundaries, enabling flux conservation across maximal achronal sets and deriving a unique covariant AL from both causal kernels and the stress-energy tensor. A central result is the one-to-one correspondence between AL and covariant representations of the causal logic (RCL), establishing a covariant, operational representation of spacetime causality in the one-particle sector. The findings lay groundwork for extending causal localization to more complex fields (e.g., Dirac, Weyl fermions) and connect localization to the broader problem of covariant quantum logic in quantum field theory, while acknowledging foundational locality obstructions that require a fully field-theoretic treatment with POVMs.

Abstract

Only recently the concept of achronal localization has been developed as the adequate frame for the description of the localizability of a relativistic quantum mechanical system. Here covariant achronal localizations are gained out of covariant conserved currents computing their flux passing through achronal surfaces. This general method is applied to the probability density currents with causal kernel regarding the massive scalar boson. As (covariant) achronal localizations correspond one-to-one to (covariant) representations of the causal logic, thus, apparently for the first time, a covariant representation of the causal logic for an elementary relativistic quantum mechanical system has been achieved. Similarly a covariant family of representations of the causal logic is derived from the stress-energy tensor of the massive scalar boson. The construction of an achronal localization from a conserved current relies on a version of the divergence theorem for open sets with almost Lipschitz boundary. This result is stated and proved in this work.