CAREER: Multiple Dirichlet Series, Automorphic Forms, and Combinatorial Representation Theory

In this proposal, Principal Investigator Brubaker intends to study automorphic forms on finite covers of split, reductive algebraic groups known as metaplectic forms. More precisely, he will investigate the Fourier-Whittaker coefficients of metaplectic Eisenstein series induced from parabolic subgroups. When the degree of the cover is trivial, this reduces to the case of Eisenstein series on linear algebraic groups as studied by Langlands, Shahidi, and others, which have been instrumental in formulating and proving portions of the Langlands program. By studying metaplectic forms in families ranging over all finite covers (including the trivial one), surprising new structure emerges. Brubaker and his collaborators have demonstrated that the resulting Fourier-Whittaker coefficients contain Dirichlet series in several complex variables (so-called ``multiple Dirichlet series'') whose coefficients are described in terms of crystal graphs. These crystal graphs encode information about representations of quantum groups, which are deformations of the universal enveloping algebra of a Lie algebra. In this situation, the relevant Lie algebra is associated to the Langlands dual group of the group on which one builds the Eisenstein series. The proposal seeks to develop this theory more completely and explore the novel connections it suggests between number theory, quantum groups and combinatorial representation theory.

Langlands' program was initially conceived as a stunning collection of conjectures relating functions with interesting arithmetic properties (e.g., counting the number of integer solutions to an equation) to functions with good analytic properties (e.g., having symmetries and being the solution of a natural differential equation). But similar kinds of duality have been observed in geometry and mathematical physics, leading to geometric and quantum versions of the Langlands programs, respectively. In short, these dualities have become a lens through which a large portion of modern mathematics and mathematical physics can be organized and understood. However, the explicit underlying mechanisms which relate, for example, arithmetic functions to analytic functions remain largely a mystery. In these projects, Principal Investigator Brubaker with his collaborators and students will use the data provided by the above special examples to attempt to find such a mechanism and attempt to better understand the relationships between various incarnations of the Langlands program in arithmetic, geometry, and physics. An equally important component of the projects is the training of students at all levels by creating a tiered system of mentoring. To bolster these efforts, a set of course materials will be developed to reflect the changing emphasis in modern number theory on analytic techniques, focusing on computational approaches and example-based learning to reinforce concepts