Title: Interacting N-vector order parameters with O(N) symmetry
Authors: A.Pelissetto (Dip. Fisica dell'Università di Roma ``La Sapienza'' and INFN, P.le Moro 2, I-00185 Roma, Italy) , E.Vicari (Dip. Fisica dell'Università di Pisa and INFN, V. Buonarroti 2, I-56127 Pisa, Italy)

We consider the critical behavior of the most general system of two N-vector order parameters that is O(N) invariant. We show that it may have a multicritical transition with enlarged symmetry controlled by the chiral O(2) \otimes O(N) fixed point. For N=2,3,4, if the system is also invariant under the exchange of the two order parameters and under independent parity transformations, one may observe a critical transition controlled by a fixed point belonging to the mn model. Also in this case there is a symmetry enlargement at the transition, the symmetry being [SO(N)⊕ SO(N)] \otimes C₂, where C₂ is the symmetry group of the square.

Key words: N-vector model, O(N) symmetry, multicritical transitions
PACS: 05.70.Jk, 64.60.Fr, 75.10.Hk