arXiv subjects

Nigel Pynn-Coates

Publications and source records attributed to Nigel Pynn-Coates.

8 recordsLinked to original sources

arXiv2025

Dimension and topology in transserial tame pairs

Every maximal Hardy field has a proper elementary differential subfield that is Dedekind complete in the maximal Hardy field. This pair of Hardy fields is a transserial tame pair, shown to have a complete and model complete elementary theory in arXiv:2408.07033. This paper introduces a dimension in transserial tame pairs and shows that it equals the (naive) dimension coming from the order topology. In particular, the dimension is definable in a certain sense, and is the unique definable dimension in a transserial tame pair. Further, transserial tame pairs are locally o-minimal and d-minimal. These properties and the dimension are used to establish topological properties of definable sets in transserial tame pairs, including a definable Baire category theorem.

math.LO↗

arXiv2025

Dimension theory for the asymptotic couple of the field of logarithmic transseries

In this paper we completely characterize all dimension functions on all models of the theory $T_{\log}$ of the asymptotic couple of the field of logarithmic transseries (Dimension Theorem). This is done by characterizing the "small" $1$-variable definable sets (Small Sets Theorem). As a byproduct, we show that $T_{\log}$ is d-minimal and does not eliminate imaginaries. Separately, we provide an abstract criterion for d-minimality, which we use to observe some new examples of d-minimal expansions of valued fields.

math.LO↗

arXiv2024

Tame pairs of transseries fields

This paper concerns pairs of models of the theory of the differential field of logarithmic-exponential transseries that are tame as a pair of real closed fields. That is, the smaller model is bounded inside the larger model and there exists a standard part map. This covers for instance the differential fields of hyperseries or surreal numbers or maximal Hardy fields equipped with suitable enlargements of the differential field of transseries. The theory of such pairs is complete and model complete in a natural language and it has quantifier elimination in the same language expanded by two predicates and a standard part map. Additionally, the smaller model is purely stably embedded in the pair, and hence so is the constant field. More generally, we study differential-Hensel-Liouville closed pre-$H$-fields, i.e., pre-$H$-fields that are differential-henselian, real closed, and closed under exponential integration, equipped with lifts of their differential residue fields, and establish similar results in that setting relative to the differential residue field.

math.LO↗

arXiv2023

Monotone $T$-convex $T$-differential fields

Let $T$ be a complete, model complete o-minimal theory extending the theory of real closed ordered fields and assume that $T$ is power bounded. Let $K$ be a model of $T$ equipped with a $T$-convex valuation ring $\mathcal{O}$ and a $T$-derivation $\partial$ such that $\partial$ is monotone, i.e., weakly contractive with respect to the valuation induced by $\mathcal{O}$. We show that the theory of monotone $T$-convex $T$-differential fields, i.e., the common theory of such $K$, has a model completion, which is complete and distal. Among the axioms of this model completion, we isolate an analogue of henselianity that we call $T^{\partial}$-henselianity. We establish an Ax--Kochen/Ershov theorem and further results for monotone $T$-convex $T$-differential fields that are $T^{\partial}$-henselian.

math.LO↗

arXiv2020

On the uniqueness of maximal immediate extensions of valued differential fields

So far there exist just a few results about the uniqueness of maximal immediate valued differential field extensions and about the relationship between differential-algebraic maximality and differential-henselianity; see arXiv:1509.02588, Chapter 7. We remove here the assumption of monotonicity in these results but replace it with the assumption that the value group is the union of its convex subgroups of finite (archimedean) rank. We also show the existence and uniqueness of differential-henselizations of asymptotic fields with such a value group.

math.AC↗

arXiv2020

Newtonian valued differential fields with arbitrary value group

The notion of newtonianity is central to the study of the ordered differential field of logarithmic-exponential transseries done by Aschenbrenner, van den Dries, and van der Hoeven; see Chapter 14 of arxiv:1509.02588. We remove the assumption of divisible value group from two of their results concerning newtonianity, namely the newtonization construction and the equivalence of newtonianity with asymptotic differential-algebraic maximality. We deduce the uniqueness of immediate differentially algebraic extensions that are asymptotically differential-algebraically maximal.

math.AC↗

arXiv2020

Differential-henselianity and maximality of asymptotic valued differential fields

We show that asymptotic (valued differential) fields have unique maximal immediate extensions. Connecting this to differential-henselianity, we prove that any differential-henselian asymptotic field is differential-algebraically maximal, removing the assumption of monotonicity from a theorem of Aschenbrenner, van den Dries, and van der Hoeven (arXiv:1509.02588, Theorem 7.0.3). Finally, we use this result to show the existence and uniqueness of differential-henselizations of asymptotic fields.

math.AC↗

arXiv2019

Model theory of differential-henselian pre-$H$-fields

Pre-$H$-fields are ordered valued differential fields satisfying some basic axioms coming from transseries and Hardy fields. We study pre-$H$-fields that are differential-Hensel-Liouville closed, that is, differential-henselian, real closed, and closed under exponential integration, establishing an Ax--Kochen/Ershov theorem for such structures: the theory of a differential-Hensel-Liouville closed pre-$H$-field is determined by the theory of its ordered differential residue field; this result fails if the assumption of closure under exponential integration is dropped. In a two-sorted setting with one sort for a differential-Hensel-Liouville closed pre-$H$-field and one sort for its ordered differential residue field, we eliminate quantifiers from the pre-$H$-field sort, from which we deduce that the ordered differential residue field is stably embedded and if it has NIP, then so does the two-sorted structure. Similarly, the one-sorted theory of differential-Hensel-Liouville closed pre-$H$-fields with closed ordered differential residue field has quantifier elimination, is the model completion of the theory of pre-$H$-fields with gap~$0$, and is complete, distal, and locally o-minimal.

math.LO↗