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We investigate the critical behavior at θ = π of the two-dimensional 0(3) nonlinear sigma model with topological term on the lattice. Our method is based on numerical simulations at imaginary values of θ, and on scaling transformations which allow a controlled analytic continuation to real values of θ. Our results are compatible with a second-order phase transition, with the critical exponent of the SU(2)1 Wess-Zumino-Novikov-Witten model, for sufficiently small values of the coupling. [ABSTRACT FROM AUTHOR]

A new approach to perform numerical simulations of systems with a θ-vacuum term is proposed, tested, and applied to CP3. The main new ingredient of this approach is the method used to compute the probability distribution function of the topological charge at θ = 0. We comment also on the possibility of applying this approach to QCD at finite baryon density. [Copyright &y& Elsevier]

Recently it has been found that in a noncompact formulation of the SU(2) gauge theory on a lattice the physical volume is larger than in the Wilson theory with the same number of sites. In its original formulation such noncompact regularization is directly applicable to U(N) theories for any N and to SU(N) theories for N=2 only. In this work we extend it to SU(N) for any N and investigate some of its properties. [Copyright &y& Elsevier]

Using the approach developed by V. Azcoiti et al. [Phys. Lett. B 563, 117 (2003)], we are able to reconstruct the behavior of the massive one-flavor Schwinger model with a θ term and a quantized topological charge. We calculate the full dependence of the order parameter with θ. Our results at θ=π are compatible with Coleman's conjecture on the phase diagram of this model. [ABSTRACT FROM AUTHOR]