Narrow Results

In this talk we present results of a recent investigation of the topological vacuum structure in SU(2) lattice gauge theory with Wilson fermions. An effective action given by the hopping parameter expansion up to the 6-th order is used. To check the reliability of this approximation we compare it with the outcomes of an exact algorithm. The topological charge is measured according to a geometric prescription.

We compare different conjugate gradient–like matrix inversion methods (CG, BiCGstab1 and BiCGstab2) employing for this purpose the compact lattice quantum electrodynamics (QED) with Wilson fermions. The main goals of this investigation are the CPU time efficiency of the methods as well as the influence of machine precision on the reliability of (physical) results especially close to the 'critical' line κ_c (β).

We discuss application of Wigner–Weyl formalism to the lattice models of condensed matter physics and relativistic quantum field theory. For the noninteracting models our technique relates Wigner transformation of the fermionic Green’s function with the Weyl symbol $Q_W$ of lattice Dirac operator. We take as an example of the model defined on rectangular lattice the model of Wilson fermions. It represents the regularization of relativistic quantum field theory and, in addition, describes qualitatively certain topological materials in condensed matter physics. In this model we derive expression for $Q_W$ in the presence of the most general case of external $U(1)$ gauge field. Next, we solve the Groenewold equation to all orders in powers of the derivatives of $Q_W$.