Role of symmetry and dimension in pseudogap phenomena

The attractive Hubbard model in d = 2 Ts studied through Monte Carlo simulations at intermediate coupling. There is a crossover temperature T-X where a pseudogap appears with concomitant precursors of Bogoliubov quasiparticles that are not local pairs. The pseudogap in A(k(F), omega) occurs in the renormalized classical regime when the correlation length is larger than the direction-dependent thermal de Broglie wavelength, xi(th) = (h) over bar nu(F)(k)/k(B)T. The ratio T-X/T-c for the pseudogap may be made arbitrarily large when the system is close to a point where the order parameter has SO(n) symmetry with n > 2. This is relevant in the context of SO(5) theories of high T-c but has more general applicability.