511 research outputs found
Some Definability Results in Abstract Kummer Theory
Let be a semiabelian variety over an algebraically closed field, and let
be an irreducible subvariety not contained in a coset of a proper algebraic
subgroup of . We show that the number of irreducible components of
is bounded uniformly in , and moreover that the bound is
uniform in families .
We prove this by purely Galois-theoretic methods. This proof applies in the
more general context of divisible abelian groups of finite Morley rank. In this
latter context, we deduce a definability result under the assumption of the
Definable Multiplicity Property (DMP). We give sufficient conditions for finite
Morley rank groups to have the DMP, and hence give examples where our
definability result holds.Comment: 21 pages; minor notational fixe
Generic Automorphisms and Green Fields
We show that the generic automorphism is axiomatisable in the green field of
Poizat (once Morleyised) as well as in the bad fields which are obtained by
collapsing this green field to finite Morley rank. As a corollary, we obtain
"bad pseudofinite fields" in characteristic 0. In both cases, we give geometric
axioms. In fact, a general framework is presented allowing this kind of
axiomatisation. We deduce from various constructibility results for algebraic
varieties in characteristic 0 that the green and bad fields fall into this
framework. Finally, we give similar results for other theories obtained by
Hrushovski amalgamation, e.g. the free fusion of two strongly minimal theories
having the definable multiplicity property. We also close a gap in the
construction of the bad field, showing that the codes may be chosen to be
families of strongly minimal sets.Comment: Some minor changes; new: a result of the paper (Cor 4.8) closes a gap
in the construction of the bad fiel
Model theory of special subvarieties and Schanuel-type conjectures
We use the language and tools available in model theory to redefine and
clarify the rather involved notion of a {\em special subvariety} known from the
theory of Shimura varieties (mixed and pure)
Involutive automorphisms of groups of finite Morley rank
We classify a large class of small groups of finite Morley rank:
-groups which are the infinite analogues of Thompson's
-groups. More precisely, we constrain the -structure of groups of finite
Morley rank containing a definable, normal, non-soluble,
-subgroup
Chai's Conjecture and Fubini properties of dimensional motivic integration
We prove that a conjecture of Chai on the additivity of the base change
conductor for semi-abelian varieties over a discretely valued field is
equivalent to a Fubini property for the dimensions of certain motivic
integrals. We prove this Fubini property when the valued field has
characteristic zero.Comment: 22 page
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