a1 School of Mathematics, University of Wales–Cardiff, Senghennydd Road, Cardiff CF2 4YH, U.K.
The norm of an integral operator occurring in the partial wave decomposition of an operator B introduced by Brown and Ravenhall in a model for relativistic one-electron atoms is determined. The result implies that B is non-negative and has no eigenvalue at 0 when the nuclear charge does not exceed a specified critical value.
(Received March 06 1997)
(Revised November 03 1997)