  We study the scattering of guided light from a multilevel cesium atom with
the transitions between the hyperfine levels $6S_{1/2}F=4$ and $6P_{3/2}F'=5$
of the $D_2$ line into the guided modes of a nanofiber. We show that the rate
of scattering of guided light from the atom in the steady-state regime into the
guided modes is asymmetric with respect to the forward and backward directions
and depends on the polarization of the probe field. The asymmetry between the
forward and backward scattering is a result of the complex transition structure
of the atom and the existence of a longitudinal component of the guided-mode
profile function. In the case of a two-level atom, the rates of spontaneous
emission (and consequently the rates of scattering) into the forward and
backward guided modes differ from each other when the atomic dipole
matrix-element vector is a complex vector in the plane that contains the fiber
axis and the atomic position.
