arXiv subjects

Masahiro Shiota

Publications and source records attributed to Masahiro Shiota.

17 recordsLinked to original sources

arXiv2024

Unstability problem of real analytic maps

As well-known, the $C^\infty$ stability of proper $C^\infty$ maps is characterized by the infinitesimal $C^\infty$ stability. In the present paper we study the counterpart in real analytic context. In particular, we show that the infinitesimal $C^ω$ stability does not imply $C^ω$ stability; for instance, a Whitney umbrella $\mathbb{R}^2 \to \mathbb{R}^3$ is not $C^ω$ stable. A main tool for the proof is a relative version of Whitney's Analytic Approximation Theorem which is shown by using H. Cartan's Theorems A and B.

math.AG↗

arXiv2017

Semialgebraic metric spcaes and resolution of singularities of definable sets

Consider the semialgebraic structure over the real field. More generally, let an ominimal structure be over a real closed field. We show that a definable metric space X with a definable metric d is embedded into a Euclidean space so that its closure is compact and the metric on the image induced by d is extended to a definable metric on the closure if and only if the limit of d(r(t);r(t)) is 0 as t converges to 0 for any definable continuous curve r from (0, 1] to X (Theorem 1). We also find two compact semialgebraic metric spaces over the real field which are isometric but not semialgebraically isometric (Theorem 2). A version of blow up is the key to the proof of Theorem 1. Using it in the same way, we prove a resolution of singularities of definable sets (Theorem 3). We prove the theorems by a constructive procedure.

math.AG↗

arXiv2017

$C^1$-triangulations of semialgebraic sets

We show that every semialgebraic set admits a semialgebraic triangulation such that each closed simplex is $C^1$ differentiable. As an application, we give a straightforward definition of the integration $\int_X ω$ over a compact semialgebraic subset $X$ of a differential form $ω$ on an ambient algebraic manifold, that provides a significant simplification of the theory of semialgebraic singular chains and integrations. Our results hold over every (possibly non-archimedian) real closed field.

math.AG↗

arXiv2016

O-minimal Hauptvermutung for polyhedra II

Hilbert initiated the standpoint in foundations of mathematics. From this standpoint, we allow only a finite number of repetitions of elementary operations when we construct objects and morphisms. When we start from a subset of a Euclidean space. Then we assume that any element of the line has only a finite number of connected components. We call the set tame if the assumption is satisfied, and define a tame morphism in the same way. In this paper we will show that a tame topological manifold is carried by a tame homeomorphism to the interior of a compact piecewise linear manifolds possibly with boundary and such a piecewise linear manifold possibly with boundary is unique up to piecewise linear homeomorphisms in the sense that if two manifolds are such PL manifolds possibly with boundary then they are the same as piecewise linear manifolds. We modify this to Theorem 2 so that argument of model theory works, and we prove it. We also consider the differentiable case.

math.GT↗

arXiv2015

Artin approximation compatible with a change of variables

We propose a version of the classical Artin approximation which allows to perturb the variables of the approximated solution. Namely, it is possible to approximate a formal solution of a Nash equation by a Nash solution in a compatible way with a given Nash change of variables. This results is closely related to the so-called nested Artin approximation and becomes false in the analytic setting. We provide local and global version of this approximation in real and complex geometry together with an application to the Right-Left equivalence of Nash maps.

math.AG↗

arXiv2014

Measuring definable sets in o-minimal fields

We introduce a non real-valued measure on the definable sets contained in the finite part of a cartesian power of an o-minimal field $R$. The measure takes values in an ordered semiring, the Dedekind completion of a quotient of $R$. We show that every measurable subset of $R^n$ with non-empty interior has positive measure, and that the measure is preserved by definable $C^1$-diffeomorphisms with Jacobian determinant equal to $\pm 1$.

math.LO↗

arXiv2014

Real Milnor Fibres and Puiseux Series

Given a real polynomial function and a point in its zero locus, we defined a set consisting of algebraic real Puiseux series naturally attached to these data. We prove that this set determines the topology and the geometry of the real Milnor fibre of the function at this point. To achieve this goal, we balance between the tameness properties of this set of Puiseux series, considered as a real algebraic object over the field of algebraic Puiseux series, and its behaviour as an infinite dimensional object over the real numbers.

math.AG↗

arXiv2013

Continuous mappings between spaces of arcs

A blow-analytic homeomorphism is an arc-analytic subanalytic homeomorphism, and therefore it induces a bijective mapping between spaces of analytic arcs. We tackle the question of the continuity of this induced mapping between the spaces of arcs, giving a positive and a negative answer depending of the topology involved. We generalise the result to spaces of definable arcs in the context of o-minimal structures, obtaining notably a uniform continuity property.

math.AG↗

arXiv2012

Virtual Poincaré polynomial of the link of a real algebraic variety

The Euler characteristic of the link of a real algebraic variety is an interesting topological invariant in order to discuss local topological properties. We prove in the paper that an invariant stronger than the Euler Characteristic is well defined for the link of an algebraic variety: its virtual Poincaré polynomial.

math.AG↗

arXiv2010

On almost Blow-analytic equivalence

Approximation of real analytic functions by Nash functions is a classical topic in real geometry. In this paper, we focus on the Nash approximation of an analytic desingularization of a Nash function germ obtained by a sequence of blowings-up along smooth analytic centers. We apply the result to prove that Nash function germs that are analytically equivalent after analytic desingularizations are Nash equivalent after Nash desingularizations. Results are based on a precise Euclidean description of a sequence of blowings-up combined with Néron Desingularization.

math.AG↗

arXiv2010

Triangulations of non-proper semialgebraic Thom maps

In [5] I solved the Thom's conjecture that a proper Thom map is triangulable. In this paper I drop the properness condition in the semialgebraic case and, moreover, in the definable case in an o-minimal structure.

math.GT↗

arXiv2010

Analytic and Nash equivalence relations of Nash maps

Let $M$ and $N$ be Nash manifolds, and $f$ and $g$ Nash maps from $M$ to $N$. If $M$ and $N$ are compact and if $f$ and $g$ are analytically R-L equivalent, then they are Nash R-L equivalent. In the local case, $C^infty$ R-L equivalence of two Nash map germs implies Nash R-L equivalence. This shows a difference of Nash map germs and analytic map germs. Indeed, there are two analytic map germs from $(R^2,0)$ to $(R^4,0)$ which are $C^infty$ R-L equivalent but not analytically R-L equivalent.

math.GT↗

arXiv2010

Triangulation of the map of a $G$-manifold to its orbit space

Let $G$ be a Lie group and $M$ a smooth proper $G$-manifold. Let $pi:Mto M/G$ denote the natural map to the orbit space. Then there exist a PL manifold $P$, a polyhedron $L$ and homeomorphisms $tau:Pto M$ and $σ:M/Gto L$ such that $σ\circpi\circτ$ is PL. If $M$ and the $G$-action are of analytic class, we can choose subanalytic $τ$ and then unique $P$ and $L$.

math.GT↗

arXiv2010

Directional properties of sets definable in o-minimal structures

In a former paper the first and third authors introduced the notion of direction set for a subset of R^n, and showed that the dimension of the common direction set of two subanalytic subsets, called directional dimension, is preserved by a bi-Lipschitz homeomorphism, provided that their images are also subanalytic. In this paper we give a generalisation of the above result to sets definable in an o-minimal structure on an arbitrary real closed field. More precisely, we first prove our main theorem and discuss in detail directional properties in the case of an Archimedean real closed field, and then we give a proof in the case of a general real closed field. In addition, related to our main result, we show the existence of special polyhedra in some Euclidean space, illustrating that the bi-Lipschitz equivalence does not always imply the existence of a definable one.

math.AG↗

arXiv2010

PL and differential topology in o-minimal structure

Arguments on PL,(=piecewise linear) topology work over any ordered field in the same way as over the real field, and those on differential topology do over a real closed field R in an o-minimal structure that expands (R,<,0,1,+,cdot). One of the most fundamental properties of definable sets is that a compact definable set in R^n is definably homeomorphic to a polyhedron (see [v]). We show uniqueness of the polyhedron up to PL homeomorphisms (o-minimal Hauptvermutung). Hence a compact definable topological manifold admits uniquely a PL manifold structure and is, so to say, tame. We also see that many problems on PL and differential topology over R can be translated to those over the real field.

math.LO↗

arXiv2009

Analytic equivalence of normal crossing functions on a real analytic manifold

By Hironaka Desingularization Theorem, any real analytic function has only normal crossing singularities after a suitable modification. We focus on the analytic equivalence of such functions with only normal crossing singularities. We prove that for such functions $C^{\infty}$ right equivalence implies analytic equivalence. We prove moreover that the cardinality of the set of equivalence classes is zero or countable.

math.AG↗

arXiv2007

On the first integral conjecture of Rene Thom

More that half a century ago R. Thom asserted in an unpublished manuscript that, generically, vector fields on compact connected smooth manifolds without boundary can admit only trivial continuous first integrals. Though somehow unprecise for what concerns the interpretation of the word \textquotedblleft generically\textquotedblright, this statement is ostensibly true and is nowadays commonly accepted. On the other hand, the (few) known formal proofs of Thom's conjecture are all relying to the classical Sard theorem and are thus requiring the technical assumption that first integrals should be of class $C^{k}$ with $k\geq d,$ where $d$ is the dimension of the manifold. In this work, using a recent nonsmooth extension of Sard theorem we establish the validity of Thom's conjecture for locally Lipschitz first integrals, interpreting genericity in the $C^{1}$ sense.

math.DS↗