The isogeny-based cryptographic protocol CSIDH is based on the group action of the class group of a particular imaginary quadratic order on certain elliptic curves. The efficiency and security of CSIDH has inspired variant protocols, such as SCALLOP and OSIDH. Such protocols are based on the vectorization problem: Given elliptic curves E, E', find the ideal class whose action on E yields E'. In this work, we provide a general understanding of this question in the context of orientations and level structure on elliptic curves.
In particular, we study a large family of generalized class groups of imaginary quadratic orders O and prove that they act freely and (essentially) transitively on the set of primitively O-oriented elliptic curves over a field k (assuming this set is non-empty) equipped with appropriate level structure. This is joint work with Wouter Castryck, Jonathan Komada Eriksen, Gioella Lorenzon, and Frederik Vercauteren.
Generalized class group actions on oriented elliptic curves with level structure
Mar. 11, 2025 12:10pm (MATH …
Kempner
Edmund Harriss (University of Arkansas)
X
Euclid's elements is regarded as an early example of proof and axiomatic methods but it also has a tradition within carpentry and construction. The straight line and circle can just as easily be regarded as abstract representations of the action of straight edge and compass just as easily as the other way round. Today we have many machines that can play the same role creating a bridge between the abstract and the physical. What potentials do they provide for realising mathematical concepts in physical space and creating manufacturing techniques?
In this talk I will look at several examples of machines with mathematical models, including affine spaces, ruled and developable surfaces and the gradient present in the grain of wood.
Mathematical Manufacturing since Euclid
Mar. 11, 2025 1:15pm (MATH 3…
PDE/Analysis
Tristan Léger (Yale University)
X
In this talk I will discuss recent and upcoming results on the boundedness of spectral projectors. The seminal work of C. Sogge gives the optimal result on any Riemannian manifold with bounded geometry for spectral windows of size 1. However when the width is smaller, the spectral projector bounds become sensitive to the global geometry of the underlying manifold. I will focus on the case of hyperbolic surfaces of infinite area, and present new estimates that hold universally in that setting. This is joint work with Jean-Philippe Anker and Pierre Germain.
Spectral projector bounds on hyperbolic surfaces of infinite area Sponsored by the Meyer Fund
Generalized class group actions on oriented elliptic curves with level structure