Spin Operators for Massive Particles

TL;DR

This paper derives and represents relativistic spin operators for massive particles from spacetime symmetry, clarifying their role in quantum phenomena and resolving longstanding inconsistencies in relativistic quantum mechanics.

Contribution

It provides a rigorous derivation of relativistic spin operators from spacetime symmetry, linking them to the Dirac equation and clarifying their physical implications.

Findings

Derivation of spin operators from spacetime symmetry.

Connection between spin operators and the Dirac equation.

Prediction of no Zitterbewegung with proper position operator.

Abstract

Since the discovery a century ago, spin describing the intrinsic angular momentum of massive elementary particles has exposed its nature and significant roles in wide ranges of (relativistic) quantum phenomena and practical applications for future quantum technology. Emerging inconsistencies have also disclosed its telltale incomplete description. Finding relativistic spins (operators) of massive particles is a long-standing fundamental problem from the beginning of relativistic quantum mechanics. Here we present the rigorous derivation and the representation of spin operators from the spacetime symmetry. The covariant parity operation, defined by the spin operators, naturally leads to a fundamental equation equivalent to the covariant Dirac equation, which manifests existent relativistic spins. Proper understanding position operator in the Dirac theory on account of the spin operator through total angular momentum predicts no Zitterbewegung as well as conserving orbital and spin currents. The spin operators can be applicable for unraveling the inconsistencies and for exploring unveiled physics of massive particles.