Large-n critical behavior of O(n) x O(m) spin models

lWe consider the Landau-Ginzburg-Wilson Hamiltonian with O(n) x O(m) symmetry and compute the critical exponents at all fixed points to O(n(-2)) and to O(epsilon (3)) in a epsilon = 4 - d expansion. We also consider the corresponding non-linear or-model and determine the fixed points and the critical exponents to O(<(<epsilon>)over tilde>(2)) in the <(<epsilon>)over tilde> = d - 2 expansion. Using these results, we draw quite general conclusions on the fixed-point structure of models with O(n) x O(m) symmetry for n large and all 2 less than or equal to d less than or equal to 4. (C) 2001 Elsevier Science B.V. All rights reserved.