L4

Given a hypersurface, the Bernstein-Sato polynomial gives deep information about its singularities.  It is defined by a D-module (the algebraic formalism of differential equations) closely related to analytic continuation of the gamma function. On the other hand, given a hypersurface (in a Calabi-Yau variety) one can also consider the Hamiltonian flow by divergence-free vector fields, which also defines a D-module considered by Etingof and myself. I will explain how, in the case of quasihomogeneous hypersurfaces with isolated singularities, the two actually coincide. As a consequence I affirmatively answer a folklore question (to which M. Saito recently found a counterexample in the non-quasihomogeneous case): if c$ is a root of the b-function, is the D-module D f^c / D f^{c+1} nonzero? We also compute this D-module, and for c=-1 its length is one more than the genus (conjecturally in the non-quasihomogenous case), matching an analogous D-module in characteristic p. This is joint work with Bitoun.
 

STAR-Vote is voting system that results from a collaboration between a number of
academics and the Travis County, Texas elections office, which currently uses a
DRE voting system and previously used an optical scan voting system. STAR-Vote
represents a rare opportunity for a variety of sophisticated technologies, such
as end-to-end cryptography and risk limiting audits, to be designed into a new
voting system, from scratch, with a variety of real world constraints, such as
election-day vote centers that must support thousands of ballot styles and run
all day in the event of a power failure.
We present and motivate the design of the STAR-Vote system, the benefits that we
expect from it, and its current status.

This is based on joint work with Josh Benaloh, Mike Byrne, Philip Kortum,
Neal McBurnett, Ron Rivest, Philip Stark, Dan Wallach
and the Office of the Travis County Clerk

Milnor has shown that three-dimensional Lie groups with left invariant Riemannian metrics furnish examples of 3-manifolds with principal Ricci curvatures of fixed signature --- except for the signatures (-,+,+), (0,+,-), and (0,+,+).  We examine these three cases on a Riemannian 3-manifold, and prove global obstructions in certain cases.  For example, if the manifold is closed, then the signature (-,+,+) is not globally possible if it is of the form -µ,f,f, with µ a positive constant and f a smooth function that never takes the values 0,-µ (this generalizes a result by Yamato '91).  Similar obstructions for the other cases will also be discussed.  Our methods of proof rely upon frame techniques inspired by the Newman-Penrose formalism.  Thus, we will close by turning our attention to four dimensions and Lorentzian geometry, to uncover a relation between null vector fields and exact symplectic forms, with relations to Weinstein structures. 

I will discuss theta-stability, a framework for analyzing moduli problems in algebraic geometry by finding a special kind of stratification called a theta-stratification, a notion which generalizes the Kempf-Ness stratification in geometric invariant theory and the Harder-Narasimhan-Shatz stratification of the moduli of vector bundles on a Riemann surface.

Our work (which is joint with Simon Smith) began as a study of the structure of infinite permutation groups $G$ in which point stabilisers are finite and all infinite normal subgroups are transitive. That led to two variations.
 

One is the generalisation in which point stabilisers are merely assumed to satisfy min-{\sc N}, the minimal condition on normal subgroups. The groups $G$ are then of two kinds. Either they have a maximal finite normal subgroup, modulo which they have either one or two minimal non-trivial normal subgroups, or they have a regular normal subgroup $M$ which is a divisible abelian $p$-group of finite rank. In the latter case the point stabilisers are finite and act irreducibly on the socle of~$M$. This leads to our second variation, which is a study of the finite linear groups that can arise.

Our work (which is joint with Simon Smith) began as a study of the structure of infinite permutation groups $G$ in which point stabilisers are finite and all infinite normal subgroups are transitive. That led to two variations. One is the generalisation in which point stabilisers are merely assumed to satisfy min-{\sc N}, the minimal condition on normal subgroups. The groups $G$ are then of two kinds. Either they have a maximal finite normal subgroup, modulo which they have either one or two minimal non-trivial normal subgroups, or they have a regular normal subgroup $M$ which is a divisible abelian $p$-group of finite rank. In the latter case the point stabilisers are finite and act irreducibly on the socle of~$M$. This leads to our second variation, which is a study of the finite linear groups that can arise.

Quantum computers derive their computational power from the ability to manipulate superposition states of quantum registers. The generic quantum attack against a symmetric encryption scheme with key length n using Grover's algorithm has O(2^(n/2)) time complexity. For this kind of attack, an adversary only needs classical access to an encryption oracle. In this talk I discuss adversaries with quantum superposition access to encryption and decryption oracles. First I review and extend work by Kuwakado and Morii showing that a quantum computer with superposition access to an encryption oracle can break the Even-Mansour block cipher with key length n using only O(n) queries. Then, improving on recent work by Boneh and Zhandry, I discuss indistinguishability notions in chosen plaintext and chosen ciphertext attacks by a quantum adversary with superposition oracle access and give constructions that achieve these security notions.

Quiver varieties, as introduced by Nakaijma, play a key role in representation theory. They give a very large class of symplectic singularities and, in many cases, their symplectic resolutions too. However, there seems to be no general criterion in the literature for when a quiver variety admits a symplectic resolution. In this talk I will give necessary and sufficient conditions for a quiver variety to admit a symplectic resolution.  This result is based on work of Crawley-Bouvey and of Kaledin, Lehn and Sorger. The talk is based on joint work with T. Schedler.