Kaluza-Klein reduction of 11-dimensional supergravity on $G_2$ manifolds yields a 4-dimensional effective field theory (EFT) with $N=1$ supersymmetry. $G_2$ manifolds are therefore the analog of Calabi-Yau (CY) threefolds in heterotic string theory. Since 2017 machine-learning techniques have been applied extensively to study CY manifolds but until 2024 no similar work had been carried out on $G_2$ manifolds. We first show how topological properties of these manifolds can be learnt using simple neural networks. We then discuss how one may try to learn Ricci-flat $G_2$ metrics with machine-learning.

Special Lagrangians form an important class of minimal submanifolds in Calabi-Yau manifolds. In this talk, we will consider the Calabi-Yau 3-folds with a K3-fibration and the size of the K3-fibres are small. Motivated by tropical geometry, Donaldson-Scaduto conjectured that special Lagrangian collapse to “gradient cycles” when the K3-fibres collapse. This phenomenon is similar to holomorphic curves in Calabi-Yau manifolds with collapsing special Lagrangian fibrations converging to tropical curves. Similar to the realization problem in tropical geometry, one might expect to reconstruct special Lagrangians from gradient cycles. In this talk, I will report the first theorem of this kind based on a joint work with Shih-Kai Chiu.

This talk explores fully nonlinear dead-core systems coupled with strong absorption terms. Our investigation reveals a chain reaction mechanism, utilizing the properties of an equation within the system to achieve higher sharp regularity across the free boundary. Furthermore, we establish geometric measure estimates and derive coincidence property for the free boundaries. We also obtain Liouville-type results for entire solutions. Notably, these findings are novel even when applied to linear systems. This is a joint work with Rafayel Teymurazyan (KAUST, Saudi Arabia, and Universidade de Coimbra, Portugal).

Weak linearisation was defined years ago through a static characterisation of the intuitive notion of virtual redex, based on (legal) paths computed from the (syntactical) term tree. Weak-linear terms impose a linearity condition only on functions that are applied (consumed by reduction) and functions that are not applied (therefore persist in the term along any reduction) can be non-linear. This class of terms was shown to be strongly normalising with deciding typability in polynomial time. We revisit this notion through non-idempotent intersection types (also called quantitative types). By using an effective characterisation of minimal typings, based on the notion of tightness, we are able to distinguish between “consumed” and “persistent” term constructors, which allows us to define an expansion relation, between general lambda-terms and weak-linear lambda-terms, whilst preserving normal forms by reduction.

A crucial problem in geometric quantization is to understand the relationship among quantum spaces associated to different polarizations. Two types of polarizations on toric varieties, Kähler and real, have been studied extensively. This talk will focus on the quantum spaces associated with mixed polarizations and explore their relationships with those associated with Kähler polarizations on toric varieties.

A Ferrers diagram is a graphical way of representing an integer partition. A q-series is a series in which the ratio of the nth term to the next is a rational function of q^{n}. With reference to the origins of the subject in the work of Sylvester, I will present a short introduction to the use of Ferrers diagrams in giving combinatorial interpretations of q-series identities. I will then move on to more recent developments involving a sort of generalized partition, called an overpartition. Finally, I will describe some further generalizations and related open problems.

3d mirror symmetry is a mysterious duality for certain pairs of hyperkähler manifolds, or more generally complex symplectic manifolds/stacks. In this talk, we will describe its relationships with 2d mirror symmetry. This could be regarded as a 3d analog of the paper Mirror Symmetry is T-Duality by Strominger, Yau and Zaslow which described 2d mirror symmetry via 1d dualities.

I will discuss some recent results obtained in collaboration with A. Figalli, S. Kim and H. Shahgholian. We consider minimizers of the Dirichlet energy among maps constrained to take values outside a smooth domain $O$ in $\mathbb{R}^m$. These minimizers can be thought of either as solutions of a vectorial obstacle problem, or as harmonic maps into the manifold-with-boundary given by the complement of $O$. I will discuss results concerning the regularity of the minimizers, the location of their singularities, and the structure of the free boundary.