Carmona, J. M.Cruz, A.Fernández Pérez, Luis AntonioJiménez, S.Martín Mayor, VíctorMuñoz Sudupe, AntonioPech, J.Ruiz Lorenzo, J. J.Tarancón, A.Téllez, P.2023-06-202023-06-202003-05-080370-269310.1016/S0370-2693(03)00382-4https://hdl.handle.net/20.500.14352/51932© 2003 Elsevier Science B.V. We thank very particularly José Luis Alonso for pointing this problem to us, for his encouragement and for many discussions. It is also a pleasure to thank Francisco Guinea for discussions. The simulations were performed in the Pentium IV cluster RTN3 at the Universidad de Zaragoza. We thank the Spanish MCyT for financial support through research contracts FPA2001-1813, FPA2000-0956, BFM2001-0718 and PB98-0842. V.M.-M. is a Ramón y Cajal research fellow (MCyT).It is shown that a bosonic formulation of the double-exchange model, one of the classical models for magnetism, generates dynamically a gauge-invariant phase in a finite region of the phase diagram. We use analytical methods, Monte Carlo simulations and finite-size scaling analysis. We study the transition line between that region and the paramagnetic phase. The numerical results show that this transition line belongs to the universality class of the antiferromagnetic RP^(2) model. The fact that one can define a universality class for the antiferromagnetic RP^(2) model, different from the one of the O(N) models, is puzzling and somehow contradicts naive expectations about universality.engjournal articlehttp://doi.org/10.1016/S0370-2693(03)00382-4http://www.sciencedirect.com/open access5351-73Antiferromagnetic RP(2) modelClassical spin systemRenormalization-groupCompeting superexchangePhase-transitions3 dimensionsOrderExponentsMagnets.Física (Física)Física-Modelos matemáticos22 Física