Phase diagram of a one-dimensional spin-orbital model

We study a one-dimensional spin-orbital model using both analytical and num erical methods. Renormalization group calculations are performed in the vic inity of a special integrable point in the phase diagram with SU(4) symmetr y. These indicate the existence of a gapless phase in an extended region of the phase diagram, missed in previous studies. This phase is SU(4) invaria nt at low energies apart from the presence of different velocities for spin and orbital degrees of freedom. The phase transition into a gapped dimeriz ed phase is in a generalized Kosterlitz-Thouless universality class. The ph ase diagram of this model is sketched using the density matrix renormalizat ion group technique.