Rarita-Schwinger particles in homogeneous magnetic fields, and inconsistencies of spin-3/2 theories

Abstract

The Rarita-Schwinger equation for a spin-3/2 particle with minimal electromagnetic coupling is solved completely in the case when a constant homogeneous external magnetic field H is present. It is shown that the spectrum of energy eigenvalues includes complex values if H is such that η=(2eH/3m³)>1, and further that the norm of the Rarita-Schwinger wave function (i.e., the total "charge" integral defined from the Lagrangian) which is positive definite for η<1 becomes indefinite (even after taking account of the constraints) when η exceeds unity. These results confirm that the difficulties in quantization first discovered by Johnson and Sudarshan are a reflection of the indefiniteness of the norm which appears already at the c-number level, and suggest that the nature of the energy spectrum (whether or not complex values are present) in the presence of very large magnetic fields would provide a quick means of predicting whether such difficulties would arise in quantization.