Gauge-invariant Mass Terms and Wave Functions

We outline a method of relating the quantum effective action and the ground state wave function of a field theory. This method, along with a gauge-invariant mass term and the previously obtained vacuum wave function, is used to arrive at the leading terms of the 3d-covariant quantum effective action for the Yang-Mills theory in three (or 2+1) dimensions. Some features of this effective action are also discussed.Comment: 10 pages, Invited talk at the International Workshop on QCD Green's functions, Confinement and Phenomenology, QCD-TNT II, September 201

Quantum mechanics on the noncommutative plane and sphere

We consider the quantum mechanics of a particle on a noncommutative plane. The case of a charged particle in a magnetic field (the Landau problem) with a harmonic oscillator potential is solved. There is a critical point, where the density of states becomes infinite, for the value of the magnetic field equal to the inverse of the noncommutativity parameter. The Landau problem on the noncommutative two-sphere is also solved and compared to the plane problem.Comment: 12 pages, no figures; references adde