P. Moretti et A. Agresti, CAN THE KLEIN-GORDON EQUATION DESCRIBE SUPERLUMINAL PROCESSES, Nuovo cimento della Societa italiana di fisica. B, Relativity, classical and statistical physics, 110(8), 1995, pp. 905-912
The possibility of a superluminal (namely, faster than c) propagation
of quantum particles is discussed in the context of the Klein-Gordon e
quation. It is found that physical conditions exist, univocally fixing
the integration path in the inverse Fourier transform representing th
e wave packet. This path excludes at all superluminal components.