  We consider the effects of Coulomb interactions on single-wall carbon
nanotubes using an on-site Hubbard interaction, u. For the (N,N) armchair tubes
the low energy theory is shown to be identical to a 2-chain Hubbard model at
half-filling, with an effective interaction u_N = u/N. Umklapp scattering leads
to gaps in the spectrum of charge and spin excitations which are exponentially
small for large N. Above the gaps the intrinsic nanotube resistivity due to
these scattering processes is linear in temperature, as observed
experimentally. The presence of "d-wave" superconductivity in the 2-chain
Hubbard model away from half-filling suggests that doped armchair nanotubes
might exhibit superconductity with a purely electronic mechanism.
