Comment on The single-wall carbon nanotube waveguides and excitation of their sigma plus pi plasmons by an electron beam [Phys. Plasmas 16, 022108 (2009)]

In a recent article [M. Nejati, C. Javaherian, B. Shokri, and B. Jazi, Phys. Plasmas 16, 022108 (2009)], Nejati studied the propagation of plasma wave in the single-wall carbon nanotubes in the presence of the electron beam and showed that the frequency of the sigma+pi plasma wave strongly depends on the nanotube radius in the short-wavelength region. Here we derive the correct form of the dispersion relation for the transverse magnetic wave in the system and show that the frequency of the plasma wave is quite sensitive to the radius of the tube in the long-wavelength limit.