Next Meeting
The 15th SEEMOD meeting will be held at Keble College, Oxford on June 13th 2023. Participants can register here.| 12:00-13:00 | Lunch |
| 13:00-14:00 | Benedikt Stock (Oxford) Title: On Fields Elementarily Characterised by their Absolute Galois Groups Abstract: Galois groups contain a lot of arithmetic information about their base fields. In this talk, I will report on fields that are elementarily completely characterised by their absolute Galois groups. We will also hint at some recent attempts and approaches to eliminate certain edge cases that appear in the classification of these fields. |
| 14:00-15:00 | Luka Ilic (Queen Mary University of London) Title: Internal Reasoning for Difference Tannakian Duality Abstract: The idea of this talk is to give a comprehensive introduction into internal logic for difference structures and illustrate its usefulness via the example of Tannakian duality. To achieve this, we will go over notions from categorical logic and explain what we mean by internal logic inside the topos of difference sets and what use it has for studying difference structures. We will talk about how to view difference fields, rings and modules and their properties in this way and finish by explaining a resulting version of Tannakian duality. |
| 15:00-15:30 | Coffee, Tea & Biscuits |
| 15:30-16:30 | Paolo Marimon (Imperial) Title: Measures in ternary homogeneous structures Abstract: We study invariant Keisler measures and MS-measurability in the context of ternary homogeneous structures. We prove that the universal homogeneous two-graph has a unique invariant Keisler measure in spite of not having any invariant type. This is related to Jahel's result that this structure is uniquely ergodic. Moreover, we prove that the generic tetrahedron-free 3-hypergraph is not MS-measurable (i.e. it does not have a dimension and a set of measures satisfying various desirable properties, such as a version of Fubini's theorem). We wanted a better understanding of the interactions between measures and higher amalgamation properties for (simple) \(\omega\)-categorical structures. Our result on the universal homogeneous two-graph implies that the measures of higher amalgamations are less well-behaved than those of 3-amalgamations, which can be studied using results of Hrushovski. In spite of these negative results, we can still obtain equations which must be satisfied by the measures of higher amalgamations in an \(\omega\)-categorical MS-measurable context. With these, we show that the generic tetrahedron-free 3-hypergraph is not MS-measurable. This is the first known example of a supersimple \(\omega\)-categorical one-based structure which is not MS-measurable. |
| 16:30-17:30 | Sylvy Anscombe (Université Paris Cité) Title: Interpretations of fragments of theories of fields Abstract: In previous work with Fehm, and then Dittmann and Fehm, we found that the existential theory of an equicharacteristic henselian valued field is axiomatised using the existential theory of its residue field, conditionally, similar to an earlier theorem of Denef and Schoutens -- giving a transfer of decidability for existential theories. In this talk I’ll describe parts of ongoing work with Fehm (in the main different to those discussed recently at CIRM) in which we use an "abstract" framework for interpreting families of incomplete theories in others in order to find transfers of decidability in various settings. I will discuss consequences for theories of PAC fields and parts of the universal-existential theory of equicharacteristic henselian valued fields. |
| 18:00-20:00 | Dinner at the Giggling Squid |
Directions to Keble College:
Via train: take the train to Oxford, then either- Walk ~20 minutes to the main entrance of Keble College.
- Take the S3 gold to the Royal Oak/Radcliffe Observatory Quarter, then walk ~5 minutes to the main entrance.
Via bus: Keble is ~10 minutes walk from Gloucester Green Bus station.
Via car: please be advised there is a zero emissions zone in place in the city centre, though this should not affect your travel to and from Keble via main roads. Beside Keble, there is pay & display parking available for max 2 hours; nearby there is an underground car park ~10 minutes walk from the main entrance of Keble. Finally, see here for Park & Ride options.
Once at Keble: Please let the porters in the lodge know you are here for SEEMOD in the Pusey Room, booked by Brian Tyrrell.
Previous meetings
The 14th SEEMOD meeting was held at the University of Buckingham on March 28th 2023.
| 12:00-13:00 | Lunch |
| 13:00-14:00 | Mark Kamsma (Imperial) Title: Categorical Neostability Abstract: Neostability focuses on developing the powerful tools and ideas for stable theories in broader, less well-behaved, classes of theories. This has been hugely successful in simple theories and more recently in NSOP1 theories. A central notion in this context is that of an independence relation, which in stable and simple theories comes from forking and in NSOP1 theories it comes from Kim-forking. There are many mathematically interesting structures that cannot be studied in the classical framework of first-order logic, but where ideas from neostability, such as independence, apply. For this reason, neostability has been developed in more general logical frameworks, such as continuous logic, positive logic and a very general category-theoretic approach that subsumes all these frameworks. In this talk I will focus on the categorical approach to independence relations, and how even in this general setting we get canonicity theorems that are surprisingly close to those we know from first-order logic. I will finish with recent examples of where the categorical framework can be applied. |
| 14:00-15:00 | Soinbhe Nic Dhonncha (Manchester) Title: Notions of flatness Abstract: Flatness of an R-module is typically defined in relation to exactness of tensor products. There are many equivalent characterisations, however, whose generalisations may not always agree. One characterisation is in terms of pure epimorphisms and positive primitive formulae. Using these as our basis, we will explore flatness in categories whose objects can be seen as certain chains of R-modules. |
| 15:00-15:30 | Coffee Break |
| 15:30-16:30 | Chieu-Minh Tran (National University of Singapore) Title: Measure doubling of small sets in \(\mathrm{SO}(3,\mathbb{R})\) Abstract: Let \(\mathrm{SO}(3,\mathbb{R})\) be the 3D-rotation group equipped with the real-manifold topology and the normalized Haar measure \(\mu\). Confirming a conjecture by Emmanuel Breuillard and Ben Green, we show that if \(A \subseteq \mathrm{SO}(3,\mathbb{R})\) is open and has sufficiently small measure, then $$ \mu(A^2) > 3.99 \mu(A).$$ We also show a more general result for the product of two sets, which can be seen as a Brunn-Minkowski-type inequality for sets with small measure in \(\mathrm{SO}(3,\mathbb{R})\). (Joint with Yifan Jing and Ruixiang Zhang) |
| 16:00-17:00 | Charlotte Kestner (Imperial) Title: Generalised measurability and bilinear forms Abstract: In this talk I will briefly go over measurable and generalised measurable structures, giving examples and non-examples. I will then go on to consider the two sorted structure (V,F,β) where V is an infinite dimensional vector space over F an infinite field, and \beta a bilinear form on this vector space. In particular I will consider the interaction of different notions of independence when this structure is pseudo finite. I will finish with some questions around generalised measurable structures. |
| 18:00-20:00 | Pub and dinner |