  Disorder effects on the density of states and electronic conduction in
metallic carbon nanotubes are analyzed by a tight binding model with Gaussian
bond disorder. Metallic armchair and zigzag nanotubes are considered. We obtain
a conductance which becomes smaller by the factor 1/2 ~ 1/3 from that of the
clean nanotube. This decrease mainly comes from lattice fluctuations of the
width which is comparable to thermal fluctuations. We also find that
suppression of electronic conductance around the Fermi energy due to disorder
is smaller than that of the inner valence (and conduction) band states. This is
a consequence of the extended nature of electronic states around the Fermi
energy between the valence and conduction bands, and is a property typical of
the electronic structures of metallic carbon nanotubes.
