Georgia Institute of Technology College of Sciences

The Seiberg-Witten equations, introduced by Edward Witten in 1994, are a first-order semilinear geometric PDE that have led to manyimportant developments in low-dimensional topology. In this talk,we study these equations on cylindrical 4-manifolds with boundary, which we supplement with (Lagrangian) boundary conditions that have a natural Morse-Floer theoretic interpretation. These boundary conditions, however, are nonlinear and nonlocal, and so the resulting PDE is highlyunusual and nontrivial. After motivating and describing the underlying geometry for the Seiberg-Witten equations with Lagrangian boundary conditions, we discuss some of the intricate analysis involved in establishing elliptic regularity for these equations, including tools from the pseudodifferential analysis ofelliptic boundary value problems and nonlinear functional analysis.

The quest for a suitable geometric description of major analyticproperties of sets has largely motivated the development of GeometricMeasure Theory in the XXth theory. In particular, the 1880 Painlev\'eproblem and the closely related conjecture of Vitushkin remained amongthe central open questions in the field. As it turns out, their higherdimensional versions come down to the famous conjecture of G. Davidrelating the boundedness of the Riesz transform and rectifiability. Upto date, it remains unresolved in all dimensions higher than 2.However, we have recently showed with A. Volberg that boundedness ofthe square function associated to the Riesz transform indeed impliesrectifiability of the underlying set. Hence, in particular,boundedness of the singular operators obtained via truncations of theRiesz kernel is sufficient for rectifiability. I will discuss thisresult, the major methods involved, and the connections with the G.David conjecture.

We discuss a global weighted estimate for a class of divergence form elliptic operators with BMO coefficients on Reifenbergflat domains. Such an estimate implies new global regularity results in Morrey, Lorentz, and H\"older spaces for solutionsof certain nonlinear elliptic equations. Moreover, it can also be used to obtain a capacitary estimate to treat a measuredatum quasilinear Riccati type equations with nonstandard growth in the gradient.

The Schur-Agler class is a subclass of the bounded analytic functions on the polydisk with close ties to operator theory. We shall describe our recent investigations into the properties of rational inner functions in this class. Non-minimality of transfer function realization, necessary and sufficient conditions for membership (in special cases), and low degree examples are among the topics we will discuss.