  We show that guiding of optical signals in chains of metal nanoparticles is
subject to a surprisingly complex dispersion relation. Retardation causes the
dispersion relation to split in two anticrossing branches, as common for
polaritons. While huge radiation losses occur above the light line, just below
the light line the micron-sized loss lengths are much longer than expected. The
anticrossing allows to create highly localized energy distributions in finite
arrays that can be tuned via the illumination wavelength. Our results apply to
all linear chains of coupled resonant scatterers.
