*** NOTE: during daylight savings time, the clock for this seminar REMAINS standard, GMT ***
E.g. 16:30 GMT = 17:30 UK time.
Zoom ID: 884 0948 8227
The seminar will focus on various expansions of o-minimal structures, such as those with o-minimal open core, d-minimal structures, H-structures, lovely pairs, RCVFs, CODFs, distal and general NIP. We target talks on pure model theory and applications. The intention is to run the seminar once every two weeks. The exact times may slightly vary, so please check below.
Upcoming talks:
April 26, 2021 (Monday) - Time: 16:30 GMT
Kobi Peterzil - University of Haifa
Title: Interpretable fields in various valued fields
Abstract:
Difficulties in analyzing interpretable objects arise when we lack (a simple) elimination of imaginaries. It turns out that in several dp-minimal settings it is possible to circumvent this difficulty by focusing on one-dimensional subsets
and by reducing these to several relatively understandable sorts.
We consider an interpretable field F in either a real closed valued field K or T-convex expansions of K. In this case one can reduce the analysis to the four sorts K, k, the value group, and K/O (for O the valuation ring), then eliminate the last two sorts, and conclude that F is either definable in the field K or in k. As a result, F is definably isomorphic to K,K(i), k or k(i).
Similar analysis can be carried out in certain P-minimal structures (in particular, in p-adically closed fields), and probably more.
(part of a joint work with Y. Halevi and A. Hasson)
May 10, 2021 (Monday) - Time: 16:30 GMT
Deirdre Haskell - McMaster University
Title: TBA
Abstract: TBA
Past talks:
April 12, 2021 (Monday) - Time: 16:30 GMT
Alexi Block Gorman - University of Illinois at Urbana-Champaign
Title: Fractal Dimensions and Definability from Büchi Automata
Abstract: Büchi automata are the natural extension of finite automata, also called finite-state machines, to a "machine" that accepts infinite-length inputs. We say a subset X of the reals is r-regular if there is a Büchi automaton that accepts (one of) the base-r expansions of every element in X, and rejects the base-r expansions of each element in its complement. We can analogously define r-regular subsets of higher arities of the reals, and these sets often exhibit fractal-like behavior--e.g., the Cantor set is 3-regular. There are several known--and remarkable--connections in logic to Büchi automata, including the fact that the expansion of the real additive group by every r-regular subset of [0,1] (for some fixed positive integer r) interprets the monadic second-order theory of the natural numbers with successor. In this talk, I will focus on some of the geometric behavior of closed r-regular sets in terms of fractal dimensions, and discuss how closed r-regular subsets of [0,1] with and without integer Hausdorff dimension form a dichotomy in terms of first order definability in expansions of the real additive group by a predicate for a specific r-regular set.
➯ RECORDING
March 29, 2021 (Monday) - Time: 16:30 GMT
Vincenzo Mantova - University of Leeds
Title: A survey on exponential-algebraic closure
Abstract:
Zilber conjectured that complex exponentiation is quasiminimal in 1997 (if not before) and produced different quasiminimal structures. He later formulated the exponential-algebraic closedness conjecture (EAC), which would imply quasiminimality of complex exponentiation.
I will summarise what has been proved so far around EAC, including extensions to abelian exponentials, modular functions, the special case of raising to powers, and an odd spin-off with o-minimal open core.
➯ RECORDING
March 15, 2021 (Monday) - Time: 16:30 GMT
Rosario Mennuni - Universität Münster
Title: The domination monoid in o-minimal theories
Abstract:
The product of invariant types and domination-equivalence are not
always compatible but, when they are, they allow to define the
"domination monoid" associated to a monster model U of a first-order theory. In the superstable case, this object parameterises
"finitely generated saturated extensions of U" and how they can be
amalgamated independently. After recalling the basic definitions
and facts, I will talk about some results from my thesis,
concerning the study of this monoid in a different context, that of
o-minimal theories. This includes a reduction of the problem to
showing generation by classes of 1-types, and a proof that this
holds in RCF. I will then discuss the open problem of showing
generation by 1-types in general, and some possible lines of
attack.
➯ RECORDING
March 1, 2021 (Monday) - Time: 16:30 GMT
Vahagn Aslanyan
-
University of East Anglia
Title: Blurrings of the j-function
Abstract: I will define blurred variants of the j-function and its derivatives, where blurring is given by the action of a subgroup of GL2(ℂ). For a dense subgroup (in the complex topology) an Existential Closedness theorem holds which states that all systems of equations in terms of the corresponding blurred j with derivatives have complex solutions, except where there is a functional transcendence reason why they should not. The proof is based on the Ax-Schanuel theorem and Remmert's open mapping theorem from complex geometry. For the j-function without derivatives we prove a stronger theorem, namely, Existential Closedness for j blurred by the action of a subgroup which is dense in GL2+(ℝ), but not necessarily in GL2(ℂ). In this case apart from the Ax-Schanuel theorem and some basic complex geometry, o-minimality is also used in the proof (I will present the proof in this case). If time permits, I will also discuss some model theoretic properties of the blurred j-function such as stability and quasiminimality. This is a joint work with Jonathan Kirby.
➯ RECORDING
February 15, 2021 (Monday) - Time: 16:30 GMT
Elliot Kaplan -
University of Illinois Urbana-Champaign
Title: Generic derivations on o-minimal structures
Abstract: Let T be a model complete o-minimal theory which extends the theory of real closed ordered fields (RCF). We introduce T-derivations: derivations on models of T which cooperate with T-definable functions. The theory of models of T expanded by a T-derivation has a model completion. If T = RCF, then this model completion is the theory of closed ordered differential fields (CODF) as introduced by Singer. We can recover many of the known facts about CODF (open core, distality) in our setting. This is joint work with Antongiulio Fornasiero.
➯ RECORDING
February 1, 2021 (Monday) - Time: 16:30 GMT
Itay Kaplan - Hebrew University of Jerusalem
Title: Compressible types in NIP theories
Abstract: I will present some work in progress joint with Martin Bays and Pierre Simon. I will discuss compressible types and relate them to uniform definability of types over finite sets (UDTFS), and to uniformity of honest definitions. All notions will be defined during the talk.
➯ RECORDING
January 18, 2021 (Monday) - Time: 16:30 GMT
Tingxiang Zou - Universität Münster
Title: Geometric random graphs
Abstract: Geometric random graphs are graphs on a countable dense set of some underlying metric space such that locally in any ball of radius one, it is a random graph. The geometric random graphs on R^n and on circles have been studied by probabilists and graph theorists. In this talk we will present some model theoretic views. In particular, we will show that under some mild assumptions, the geometric random graphs based on a fixed metric space will have the same theory. We will also talk about some geometric properties of the underlying metric space that can be recovered from the graphs. This is a work in progress joint with Omer Ben-Neria and Itay Kaplan.
➯ RECORDING
January 4, 2021 (Monday) - Time: 16:30 GMT
Chris Miller - Ohio State University
Title: Connectedness in structures on the real numbers
Abstract: We consider structures on the set of real numbers having the property that connected components of definable sets are definable. Our main analytic-geometric result is that any such expansion of the real additive group by boolean combinations of closed sets (of any arities) is either o-minimal (with respect the usual order) or undecidable, and if the set of integers is definable, then so is integer multiplication. It is known that all o-minimal structures on the real line have the property, as do all expansions of the real field that define the integers (easy modulo some basic descriptive set theory). We show that fusions of the real ordered additive group with expansions of the ring of integers are also examples. All results hold with "connected component" replaced by "path component" or "quasicomponent". (Joint with A. Dolich, A. Savatovsky and A. Thamrongthanyalak. Preprint available on MODNET and arXiv.)
➯ RECORDING
December 21, 2020 (Monday) - Time: 16:30 GMT
Christian d'Elbée - Hebrew University of Jerusalem
Title: Generic expansions by a reduct
Abstract: Consider the expansion TS of a theory T by a predicate for a submodel of a reduct T0 of T. This generalizes the generic predicate construction and some theories of lovely pairs. We present a setup in which this expansion admits a model companion TS. We show that the nice features of the theory T transfer to TS. In particular, by studying independence relations, we find conditions for which this expansion preserves the NSOP1, simplicity or stability of the starting theory T. We will also give concrete examples of new model-companion obtained by this process, among them new NSOP1 theories such as the expansion of an algebraically closed field of positive characteristic by an additive subgroup (ACFG) and the expansion of an algebraically closed field of any characteristic by a generic multiplicative subgroup. This construction also gives some very wild expansions of fields, such as the expansion of an algebraically closed valued field of positive characteristic by a generic additive subgroup, which has TP1 and TP2.
➯ RECORDING
December 7, 2020 (Monday) - Time: 16:30 GMT
Artem Chernikov - University of California, Los Angeles
Title: Distality in valued fields and related structures
Abstract:
In this talk we discuss distality, a model-theoretic notion of tameness generalizing o-minimality, in valued fields and related structures. In particular, we characterize distality in certain ordered abelian groups, provide an Ax-Kochen-Ershov style characterization for henselian valued fields, and demonstrate that certain expansions of fields, e.g. the valued differential field of logarithmic-exponential transseries, are distal. This relies in particular on a general quantifier elimination result for pure short exact sequences of abelian groups. Joint work with Matthias Aschenbrenner, Allen Gehret and Martin Ziegler.
➯ RECORDING
November 23, 2020 (Monday) - Time: 16:30 GMT
Alexander Berenstein - Universidad de Los Andes
Title: A review of expansions by predicates and some preservation theorems
Abstract: We say that a theory is geometric if the algebraic closure satisfies the exchange property and eliminates the quantifier exists infinitely.
Examples include dense o-minimal theories, strongly minimal theories and SU-rank one theories. In this talk we will introduce geometric theories, review
some of its expansions by predicates and the structural properties (stability, simplicity, NIP, NTP2) that these expansions preserve.
➯ RECORDING
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