  Chiral surface states in topological insulators are robust against
interactions, non-magnetic disorder and localization, yet topology does not
yield protection in transport. This work presents a theory of interacting
topological insulators in an external electric field, starting from the quantum
Liouville equation for the many-body density matrix. Out of equilibrium,
topological insulators acquire a current-induced spin polarization.
Electron-electron interactions renormalize the non-equilibrium spin
polarization and charge conductivity, and disorder in turn enhances this
renormalization by a factor of two. Topological insulator phenomenology remains
intact in the presence of interactions out of equilibrium, and an exact
correspondence exists between the mathematical frameworks necessary for the
understanding of the interacting and non-interacting problems.
