30 research outputs found
Definable and invariant types in enrichments of NIP theories
Let T be an NIP L-theory and T' be an enrichment. We give a sufficient
condition on T' for the underlying L-type of any definable (respectively
invariant) type over a model of T' to be definable (respectively invariant) as
an L-type. Besides, we generalise work of Simon and Starchenko on the density
of definable types among non forking types to this relative setting. These
results are then applied to Scanlon's model completion of valued differential
fields.Comment: 9 pages. An error was pointed out in section 2 of the previous
version so that section was removed. So was Proposition 3.8 that depended on
i
Valued fields, Metastable groups
We introduce a class of theories called metastable, including the theory of
algebraically closed valued fields (ACVF) as a motivating example. The key
local notion is that of definable types dominated by their stable part. A
theory is metastable (over a sort ) if every type over a sufficiently
rich base structure can be viewed as part of a -parametrized family of
stably dominated types. We initiate a study of definable groups in metastable
theories of finite rank. Groups with a stably dominated generic type are shown
to have a canonical stable quotient. Abelian groups are shown to be
decomposable into a part coming from , and a definable direct limit
system of groups with stably dominated generic. In the case of ACVF, among
definable subgroups of affine algebraic groups, we characterize the groups with
stably dominated generics in terms of group schemes over the valuation ring.
Finally, we classify all fields definable in ACVF.Comment: 48 pages. Minor corrections and improvements following a referee
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Imaginaries in separably closed valued fields
We show that separably closed valued fields of finite imperfection degree
(either with lambda-functions or commuting Hasse derivations) eliminate
imaginaries in the geometric language. We then use this classification of
interpretable sets to study stably dominated types in those structures. We show
that separably closed valued fields of finite imperfection degree are
metastable and that the space of stably dominated types is strict
pro-definable
Definable equivalence relations and zeta functions of groups
We prove that the theory of the -adics admits elimination
of imaginaries provided we add a sort for for each . We also prove that the elimination of
imaginaries is uniform in . Using -adic and motivic integration, we
deduce the uniform rationality of certain formal zeta functions arising from
definable equivalence relations. This also yields analogous results for
definable equivalence relations over local fields of positive characteristic.
The appendix contains an alternative proof, using cell decomposition, of the
rationality (for fixed ) of these formal zeta functions that extends to the
subanalytic context.
As an application, we prove rationality and uniformity results for zeta
functions obtained by counting twist isomorphism classes of irreducible
representations of finitely generated nilpotent groups; these are analogous to
similar results of Grunewald, Segal and Smith and of du Sautoy and Grunewald
for subgroup zeta functions of finitely generated nilpotent groups.Comment: 89 pages. Various corrections and changes. To appear in J. Eur. Math.
So
Games and Strategies as Event Structures.
In 2011, Rideau and Winskel introduced concurrent games and strategies as
event structures, generalizing prior work on causal formulations of games. In this paper we give a detailed, self-contained and slightly-updated account of the results of Rideau and Winskel: a notion of pre-strategy based on event structures; a characterisation of those pre-strategies (deemed strategies) which are preserved by composition with a copycat strategy; and the construction of a bicategory of these strategies. Furthermore, we prove
that the corresponding category has a compact closed structure, and hence forms the basis for the semantics of concurrent higher-order computation
Imaginaries, invariant types and pseudo p-adically closed fields
In this paper, we give a general criterion for elimination of imaginaries using an abstract independence relation. We also study germs of definable functions at certain well-behaved invariant types. Finally we apply these results to prove the elimination of imaginaries in bounded pseudop-adically closed fields.ValCoMo/[ANR-13-BS01-0006]//UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigaciones en Matemáticas Puras y Aplicadas (CIMPA
Hensel minimality
We present Hensel minimality, a new notion for non-archimedean tame geometry
in Henselian valued fields. This notion resembles o-minimality for the field of
reals, both in the way it is defined (though extra care for parameters of unary
definable sets is needed) and in its consequences. In particular, it implies
many geometric results that were previously known only under stronger
assumptions like analyticity. As an application we show that Hensel minimality
implies the existence of t-stratifications, as defined previously by the second
author. Moreover, we obtain Taylor approximation results which lay the ground
for analogues of point counting results by Pila and Wilkie, for analogues of
Yomdin's -parameterizations of definable sets, and for -adic and
motivic integration.Comment: 90 page
Definable equivalence relations and zeta functions of groups
The authors wish to thank Thomas Rohwer, Deirdre Haskell, Dugald Macpherson and Elisabeth Bouscaren for their comments on earlier drafts of this work, Martin Hils for suggesting that the proof could be adapted to finite extensions and Zo´e Chatzidakis for pointing out an error in how constants were handled in earlier versions. The second author is grateful to Jamshid Derakhshan, Marcus du Sautoy, Andrei Jaikin-Zapirain, Angus Macintyre, Dugald Macpherson, Mark Ryten, Christopher Voll and Michele Zordan for helpful conversations. We are grateful to Alex Lubotzky for suggesting studying representation growth; several of the ideas in Section 8 are due to him. The first author was supported by the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013) / ERC Grant agreement no. 291111/ MODAG, the second author was supported by a Golda Meir Postdoctoral Fellowship at the Hebrew University of Jerusalem and the third author was partly supported by ANR MODIG (ANR-09-BLAN-0047) Model Theory and Interactions with Geometry. The author of the appendix would like to thank M. du Sautoy, C. Voll, and Kien Huu Nguyen for interesting discussions on this and related subjects. He was partially supported by the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013) with ERC Grant Agreement nr. 615722 MOTMELSUM and he thanks the Labex CEMPI (ANR-11-LABX-0007-01). We are grateful to the referee for their careful reading of the paper and for their many comments, corrections and suggestions for improving the exposition. In memory of Fritz Grunewald.Peer reviewedPostprin