Gravitationally Coupled Dirac Equation for Antimatter

TL;DR

This paper revisits the gravitationally coupled Dirac equation, corrects previous derivations, and demonstrates that particles and antiparticles experience identical gravitational interactions, supporting the consistency of quantum mechanics with general relativity.

Contribution

It provides a corrected derivation of the gravitationally coupled Dirac equation and shows particle-antiparticle symmetry in gravitational coupling for Schwarzschild-type metrics.

Findings

Corrected the affine connection matrix prefactor.

Established symmetry between particle and antiparticle solutions.

Confirmed equal gravitational coupling for matter and antimatter.

Abstract

The coupling of antimatter to gravity is of general interest because of conceivable cosmological consequences ("surprises") related to dark energy and the cosmological constant. Here, we revisit the derivation of the gravitationally coupled Dirac equation and find that the prefactor of a result given previously in [D.R. Brill and J.A. Wheeler, Rev. Mod. Phys., vol. 29, p. 465 (1957)] for the affine connection matrix is in need of a correction. We also discuss the conversion the curved-space Dirac equation from East-Coast to West-Coast conventions, in order to bring the gravitationally coupled Dirac equation to a form where it can easily be unified with the electromagnetic coupling as it is commonly used in modern particle physics calculations. The Dirac equation describes anti-particles as negative-energy states. We find a symmetry of the gravitationally coupled Dirac equation, which connects particle and antiparticle solutions for a general space-time metric of the Schwarzschild type and implies that particles and antiparticles experience the same coupling to the gravitational field, including all relativistic quantum corrections of motion. Our results demonstrate the consistency of quantum mechanics with general relativity and imply that a conceivable difference of gravitational interaction of hydrogen and antihydrogen should directly be attributed to a a "fifth force" ("quintessence").