  We present a detailed comparison between theoretical predictions on electron
scattering processes in metallic single-walled carbon nanotubes with defects
and experimental data obtained by scanning tunneling spectroscopy of Ar$^+$
irradiated nanotubes. To this purpose we first develop a formalism for studying
quantum transport properties of defected nanotubes in presence of source and
drain contacts and an STM tip. The formalism is based on a field theoretical
approach describing low-energy electrons. We account for the lack of
translational invariance induced by defects within the so called extended kp
approximation. The theoretical model reproduces the features of the
particle-in-a-box-like states observed experimentally. Further, the comparison
between theoretical and experimental Fourier-transformed local density of state
maps yields clear signatures for inter- and intra-valley electron scattering
processes depending on the tube chirality.
