  A theoretical analysis of electromagnetic forces on neutral particles in an
hollow waveguide is presented. We show that the effective scattering cross
section of a very small (Rayleigh) particle can be strongly modified inside a
waveguide. The coupling of the scattered dipolar field with the waveguide modes
induce a resonant enhanced backscattering state of the scatterer-guide system
close to the onset of new modes. The particle effective cross section can then
be as large as the wavelength even far from any transition resonance. As we
will show, a small particle can be strongly accelerated along the guide axis
while being highly confined in a narrow zone of the cross section of the guide.
