In Born-Infeld theory and other nonlinear electrodynamics, the presence of a
magnetostatic field modifies the dispersion relation and the energy velocity of
waves propagating in a hollow waveguide. As a consequence, the transmitted
power along a waveguide suffers slight changes when a magnetostatic field is
switched on and off. This tiny effect could be better tested by operating the
waveguide at a frequency close to the cutoff frequency.Comment: 5 pages. Version to appear in Journal of Physics
