  The T-matrix is a powerful tool that provides the complete description of the
linear interaction between the electromagnetic field and a given object. In
here, we generalize the usual monochromatic formalism to the case of
polychromatic field-matter interaction. The group of transformations of special
relativity provides the guidance for building the new formalism, which is
inherently polychromatic. The polychromatic T-matrix affords the direct
treatment of the interaction of electromagnetic pulses with objects, even when
the objects move at constant relativistic speeds.
