Differential and Integral Operators on Riemann Surfaces and the Geometry and Algebra of Sewing

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This proposal involves complex analysis, Riemann surfaces and Teichmuller theory, and conformal field theory.    Complex analysis is the study of the calculus of complex numbers. It is an indispensable tool in mathematics, engineering, and physics, among other fields. Riemann surfaces are the primary objects of complex analysis, which are two--dimensional shapes with enough structure to define angles, and maps between them which preserve angles on a very fine scale. Riemann surfaces arise naturally when considering certain kinds of differential equations, and have applications to cryptography and theoretical physics. Teichmuller theory is the systematic study of deformations of Riemann surfaces, as well as the geometry of the collection of Riemann surfaces as a whole.    Conformal field theory is the study of physical systems which are invariant under small--scale re-scalings and rotations. It has applications to statistical mechanics and quantum field theory. The mathematical study of conformal field theory involves both the problem of making a rigorous physical model, as well as exploring the rich mathematical consequences of the physical ideas of the theory.    My research involves nested surfaces, where the edges of the inner surfaces are very rough curves called quasicircles. These are inevitable in the theory of Riemann surfaces, and occur naturally in certain kinds of random processes; for example, percolation and random walks. Many fractals are examples of quasicircles. The long--term aim of the research is to understand and relate the geometry, algebra, and analysis of these nested surfaces. The surfaces themselves have geometric properties, as does the entire infinite-dimensional collection of surfaces. The algebraic structure comes from a procedure called sewing, in which surfaces are joined along their edges; this structure arises both in physics and Teichmuller theory. The seams are, in general, quasicircles. The analysis arises in the study of spaces of complex analytic or harmonic maps and operators on these spaces. All three aspects interact: the geometry manifests itself in invariants, which are quantities unchanged under algebraic operations arising from sewing; the invariants can be written analytically in terms of the operators on function spaces; and the algebraic operations can be expressed analytically in terms of their action on the function spaces and operators. More technically speaking, the goals include index theorems for conformal invariants and construction of global analytic quantities such as a Kahler potential on Teichmuller space, period matrices, and determinant line bundles.   The results obtained will be used by researchers in the global analysis and geometry of Riemann surfaces, Teichmüller theory, boundary value problems in complex analysis, and conformal field theory.  The establishment of fundamental connections between these fields will stimulate new research and unexpected insights in the long term.