Thu, 02 Feb 2023
17:00
L3

Geometric Stability Theory and the Classification of Unstable Structures

Scott Mutchnik
(University of California, Berkeley)
Abstract

The equivalence of NSOP${}_1$ and NSOP${}_3$, two model-theoretic complexity properties, remains open, and both the classes NSOP${}_1$ and NSOP${}_3$ are more complex than even the simple unstable theories. And yet, it turns out that classical geometric stability theory, in particular the group configuration theorem of Hrushovski (1992), is capable of controlling classification theory on either side of the NSOP${}_1$-SOP${}_3$ dichotomy, via the expansion of stable theories by generic predicates and equivalence relations. This allows us to construct new examples of strictly NSOP${}_1$ theories. We introduce generic expansions corresponding, though universal axioms, to definable relations in the underlying theory, and discuss the existence of model companions for some of these expansions. In the case where the defining relation in the underlying theory $T$ is a ternary relation $R(x, y, z)$ coming from a surface in 3-space, we give a surprising application of the group configuration theorem to classifying the corresponding generic expansion $T^R$. Namely, when $T$ is weakly minimal and eliminates the quantifier $\exists^{\infty}$, $T^R$ is strictly NSOP${}_4$ and TP${}_2$ exactly when $R$ comes from the graph of a type-definable group operation; otherwise, depending on whether the expansion is by a generic predicate or a generic equivalence relation, it is simple or NSOP${}_1$.

Counting graphic sequences via integrated random walks
Balister, P Donderwinkel, S Groenland, C Johnston, T Scott, A (17 Jan 2023) http://arxiv.org/abs/2301.07022v2
Corrigendum to “Nonlinear matrix recovery using optimization on the Grassmann manifold” [Appl. Comput. Harmon. Anal. 62 (2023) 498–542]
Goyens, F Cartis, C Eftekhari, A Applied and Computational Harmonic Analysis volume 63 93 (01 Mar 2023)
The Ratios Conjecture and upper bounds for negative moments of L-functions over function fields
Bui, H Florea, A Keating, J Transactions of the American Mathematical Society volume 376 issue 6 4453-4510 (21 Mar 2023)
Decomposing random permutations into order-isomorphic subpermutations
Groenland, C Johnston, T Korandi, D Roberts, A Scott, A Tan, J SIAM Journal on Discrete Mathematics volume 37 issue 2 1252-1261 (22 Jun 2023)
Mon, 06 Feb 2023
16:30
L4

Singularities along the Lagrangian mean curvature flow of surfaces

Felix Schulze
(Warwick)
Abstract
It is an open question to determine which Hamiltonian isotopy classes of Lagrangians in a Calabi-Yau manifold have a special Lagrangian representative. One approach is to follow the steepest descent of area, i.e. the mean curvature flow, which preserves the Lagrangian condition. But in general such a flow will develop singularities in finite time, and it has been open how to continue the flow past singularities. We will give an introduction to the problem and explain recent advances where we show that in the simplest possible situation, i.e. the Lagrangian mean curvature flow of surfaces, when the singularity is the special Lagrangian union of two transverse planes, then the flow forms a “neck pinch”, and can be continued past the singularity. This is joint work with Jason Lotay and Gábor Székelyhidi.
Moments of moments of the characteristic polynomials of random orthogonal and symplectic matrices
Claeys, T Forkel, J Keating, J Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences volume 479 (22 Feb 2023)
Geometric analysis enables biological insight from complex non-identifiable models using simple surrogates
Browning, A Simpson, M PLoS Computational Biology volume 19 issue 1 (20 Jan 2023)
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