Geometry of moduli stacks of Galois representations

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A central problem in number theory concerns solving polynomial equations in the whole numbers and closely related number systems. Solving these so-called Diophantine equations is typically very difficult, and this difficulty is a source of security for encryption algorithms that, for instance, guarantee private communication on the internet. Moreover, the richness of these Diophantine problems has profound connections to other branches of mathematics. One can fruitfully study the set of solutions to these equations through its geometry and dynamics, repackaging them as a Galois representation. In the 1970s, Robert Langlands made far-reaching predictions that connect Galois representations to mathematical physics and harmonic analysis. A p-adic version of Langlands' conjectures, which incorporates divisibility by powers of a prime, has led to exciting progress on Langlands' original conjectures and, consequently, a range of classical number-theoretic questions like Fermat's Last Theorem. Further analogues of Langlands' conjectures in other contexts have spurred activity in representation theory, algebraic geometry, and modern physics. More recently, a number of mathematicians have proposed a unifying categorical framework for these different versions of Langlands' conjectures. This project aims to study the p-adic version of Langlands' conjectures through the categorical framework by modelling the space of Galois representations. The geometry of the space of Galois representations is a new and fertile research direction that provides opportunities to train younger researchers and to connect communities in number theory and geometric representation theory. The PI also plans to recruit and train researchers through outreach, by disseminating accessible background material on number theory aimed at beginning graduate students, and by organizing local and regional seminars and conferences.The goal of this project is to investigate the hypothetical mod p and p-adic Langlands correspondences that relate Galois representations and modular and integral representations of p-adic reductive groups. This correspondence is conjecturally mediated by sheaves on stacks of Galois representations. The Principal Investigator will construct local models for stacks of Galois representations to analyze these conjectural sheaves and answer questions around modularity lifting, the Breuil-Mezard conjecture, the weight part of Serre's conjecture, and the mod p cohomology of locally symmetric spaces using the Taylor-Wiles method. These investigations will allow for applications to and from modular and geometric representation theory. This project gives undergraduate and graduate students the opportunity to probe local models via combinatorial methods and computer algebra packages.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.