Noncommutative Gauge Theory beyond the Canonical Case
  In this thesis noncommutative gauge theory is extended beyond the canonical case, i.e. to structures where the commutator no longer is a constant. In the first part noncommutative spaces created by star-products are studied. We are able to identify differential operators that still have an undeformed Leibniz rule and can therefore be gauged much in the same way as in the canonical case. By linking these derivations to frames (vielbeins) of a curved manifold, it is possible to formulate noncommutative gauge theories that admit nonconstant noncommutativity and go to gauge theory on curved spacetime in the commutative limit. We are also able to express the dependence of the noncommutative quantities on their corresponding commutative counterparts by using Seiberg-Witten maps. In the second part we study noncommutative gauge theory in the matrix theory approach. There, the noncommutative space is a finite dimensional matrix algebra (fuzzy space) which emerges as the ground state of a matrix action, the fluctuations around this ground state creating the gauge theory. This gauge theory is finite, goes to gauge theory on a 4-dimensional manifold in the commutative limit and can also be used to regularize the noncommutative gauge theory of the canonical case. In particular, we are able to match parts of the known instanton sector of the canonical case with the instantons of the finite theory. 
Wolfgang Behr