CAREER: Polynomials, Geometry, and Dynamics

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Dynamical systems are all around us: they govern the motion of the planets, the weather, the stock market, the ecosystems in which we live. These systems depend on a variety of parameters, and as these parameters change, the corresponding system is affected. Understanding how dynamical systems change with different parameters is a very complicated and delicate question which is not even completely understood in the simplest of mathematical models. The research outlined in this proposal explores connections between different perspectives on parameter spaces associated to particular dynamical systems. For example, one of the most intriguing ways to view these parameter spaces is algebraically; that is, these parameters spaces are intimately related of roots of polynomials, an area of mathematics that, a priori, has no obvious connection to dynamics. Investigating these mysterious and somewhat surprising connections is one of the main research goals outlined in this proposal. This proposal also contains a substantial outreach component to share mathematics with high school students through mathematical fieldtrips to the Mathematics Department at the University of Michigan, and to give graduate students and postdocs opportunities to learn from each other through a series of workshops, which will be followed by companion conferences at the University of Michigan. A major goal in the field of complex dynamics is to understand dynamical moduli spaces. The most successful endeavor in this regard has been the study of the moduli space of quadratic polynomials where the Mandelbrot set lives; the Mandelbrot set is a universal object in complex dynamics. Much of the structure of the Mandelbrot set can actually be revealed through algebraic data; that is, there are distinguished algebraic integers in the Mandelbrot set (ie, roots of a certain collection of polynomials with integer coefficients), and these points are dense in the boundary. In the first part of this proposal, we consider collections of algebraic integers (or roots of collections of polynomials) arising naturally in the parameter space of an iterated function system. We take the topological closure of these roots and (following some work of others) develop a dynamical theory of the iterated function system to better understand the structure of this set. Much of the discussion unfolds in a way parallel to that for quadratic polynomials except there are some surprising differences and still many interesting questions to explore which link geometry, dynamics, algebra, and Galois theory. The second part of this proposal is centered around algebraic data and Thurston's Topological Characterization of Rational Maps, one of the most important theorems in complex dynamics. Associated to a postcritically finite rational map on the Riemann sphere, are three different kinds of linear operators. These operators naturally arise in the setting of Thurston's theorem, each acting on a finite-dimensional vector space. The characteristic polynomials of these operators have rational coefficients, so the corresponding eigenvalues are algebraic. This proposal explores possible connections that these operators (and their eigenvalues) have with each other, and connections that these operators (and their eigenvalues) have with the geometry and dynamics of the original rational map.