  We study nonlinear transport for two coupled one-dimensional quantum wires or
carbon nanotubes described by Luttinger liquid theory. Transport properties are
shown to crucially depend on the contact length $L_c$. For a special
interaction strength, the problem can be solved analytically for arbitrary
$L_c$. For point-like contacts and strong interactions, a qualitatively
different picture compared to a Fermi liquid emerges, characterized by
zero-bias anomalies and strong dependence on the applied cross voltage. In
addition, pronounced Coulomb drag phenomena are important for extended
contacts.
