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Documents  Pichon, Anne | enregistrements trouvés : 11

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Algebraic and Complex Geometry

Let $(V,p)$ be a complex isolated complete intersection singularity germ (an ICIS). It is well-known that its Milnor number $\mu$ can be expressed as the difference:
$$\mu = (-1)^n ({\rm Ind}_{GSV}(v;V) - {\rm Ind}_{rad}(v;V)) \;,$$
where $v$ is a continuous vector field on $V$ with an isolated singularity at $p$, the first of these indices is the GSV index and the latter is the Schwartz (or radial) index. This is independent of the choice of $v$.
In this talk we will review how this formula extends to compact varieties with non-isolated singularities. This depends on two different ways of extending the notion of Chern classes to singular varieties. On elf these are the Fulton-Johnson classes, whose 0-degree term coincides with the total GSV-Index, while the others are the Schwartz-McPherson classes, whose 0-degree term is the total radial index, and it coincides with the Euler characteristic. This yields to the well known notion of Milnor classes, which extend the Milnor number. We will discuss some geometric facts about the Milnor classes.
Let $(V,p)$ be a complex isolated complete intersection singularity germ (an ICIS). It is well-known that its Milnor number $\mu$ can be expressed as the difference:
$$\mu = (-1)^n ({\rm Ind}_{GSV}(v;V) - {\rm Ind}_{rad}(v;V)) \;,$$
where $v$ is a continuous vector field on $V$ with an isolated singularity at $p$, the first of these indices is the GSV index and the latter is the Schwartz (or radial) index. This is independent of the choice ...

32S65 ; 14B05 ; 57R20

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Algebraic and Complex Geometry

We review basic results on determinantal varieties and show how to apply methods of singularity theory of matrices to study their invariants and geometry. The Nash transformation and the Euler obstruction of Essentially Isolated Determinantal Singularities (EIDS) are discussed. To illustrate the results we compute the Euler obstruction of corank one EIDS with non isolated singularities.

14B05 ; 32S05

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- 1065 p.
ISBN 978-981-270410-8

Localisation : Colloque 1er étage (MARS)

classe caractéristique # désingularisation # singularités de courbes planes # polytope # forme symplectique singulière # résolution de singularités # fibre de Milnor # surface singulière # variété torique

14-06 ; 32-06 ; 58-06 ; 00B25 ; 32Sxx

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Algebraic and Complex Geometry

Let $(X,0)$ be an ICIS of dimension $2$ and let $f :(X,0)\to\mathbb{C} ^2$ be a map germ with an isolated instability. Given $F : (\mathcal{X} , 0) \to (\mathbb{C} \times \mathbb{C}^2, 0)$ a stable unfolding of $f$, we look to the invariants related to the family $f_s$ and we find relations between them. We obtain necessary and sufficient conditions for $F$ to be Whitney equisingular. (Joint work with B. Orfice-Okamoto and J. N. Tomazella)

32S30 ; 58K15 ; 58K40 ; 32S05

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Algebraic and Complex Geometry

Pham and Teissier showed in the late 60’s that any two plane curve germs with the same outer Lipschitz geometry have equivalent embeddings into $\mathbb{C}^2$. We consider to what extent the same holds in higher dimensions, giving examples of normal surface singularities which have the same topology and outer Lipschitz geometry but whose embeddings into $\mathbb{C}^3$ are topologically inequivalent. Joint work with Anne Pichon.

Keywords: bilipschitz - Lipschitz geometry - normal surface singularity - Zariski equisingularity - Lipschitz equisingularity
Pham and Teissier showed in the late 60’s that any two plane curve germs with the same outer Lipschitz geometry have equivalent embeddings into $\mathbb{C}^2$. We consider to what extent the same holds in higher dimensions, giving examples of normal surface singularities which have the same topology and outer Lipschitz geometry but whose embeddings into $\mathbb{C}^3$ are topologically inequivalent. Joint work with Anne Pichon.

Keywords: ...

14B05 ; 32S25 ; 32S05 ; 57Mxx

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Algebraic and Complex Geometry

This talk will describe ongoing joint work with Paul Cadman and Duco van Straten, based on the PhD thesis of the former. Givental and Varchenko used the period mapping to pull back the intersection form on the Milnor fibre of an irreducible plane curve singularity $C$, and thereby define a symplectic structure on the base space of a miniversal deformation. We show how to combine this with a symmetric basis for the module of vector fields tangent to the discriminant, to produce involutive ideals $I_k$ which define the strata of parameter values $u$ such that $\delta(C_u)\leq k$. In the process we find an unexpected Lie algebra and a still mysterious canonical deformation of the module structure of the critical space over the discriminant. Much of this work is experimental - a crucial gap in understanding still needs bridging. This talk will describe ongoing joint work with Paul Cadman and Duco van Straten, based on the PhD thesis of the former. Givental and Varchenko used the period mapping to pull back the intersection form on the Milnor fibre of an irreducible plane curve singularity $C$, and thereby define a symplectic structure on the base space of a miniversal deformation. We show how to combine this with a symmetric basis for the module of vector fields tangent ...

14H20 ; 14H50 ; 32S30

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Algebraic and Complex Geometry

The Jacobian algebra, obtained from the ring of germs of functions modulo the partial derivatives of a function $f$ with an isolated singularity, has a non-degenerate bilinear form, Grothendieck Residue, for which multiplication by $f$ is a symmetric nilpotent operator. The vanishing cohomology of the Milnor Fibre has a bilinear form induced by cup product for which the nilpotent operator $N$, the logarithm of the unipotent part of the monodromy, is antisymmetric. Using the nilpotent operators we obtain primitive parts of the bilinear form and we compare both bilinear forms. In particular, over $\mathbb{R}$, we obtain signatures of these primitive forms, that we compare. The Jacobian algebra, obtained from the ring of germs of functions modulo the partial derivatives of a function $f$ with an isolated singularity, has a non-degenerate bilinear form, Grothendieck Residue, for which multiplication by $f$ is a symmetric nilpotent operator. The vanishing cohomology of the Milnor Fibre has a bilinear form induced by cup product for which the nilpotent operator $N$, the logarithm of the unipotent part of the ...

14B05 ; 32S65 ; 32S55

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Algebraic and Complex Geometry

We study germs of singular varieties in a symplectic space. We introduce the algebraic restrictions of differential forms to singular varieties and prove the generalization of Darboux-Givental' theorem from smooth submanifolds to arbitrary quasi-homogeneous varieties in a symplectic space. Using algebraic restrictions we introduce new symplectic invariants and explain their geometric meaning. We show that a quasi-homogeneous variety $N$ is contained in a non-singular Lagrangian submanifold if and only if the algebraic restriction of the symplectic form to $N$ vanishes. The method of algebraic restriction is a powerful tool for various classification problems in a symplectic space. We illustrate this by the construction of a complete system of invariants in the problem of classifying singularities of immersed $k$-dimensional submanifolds of a symplectic 2n-manifold at a generic double point.

Keywords: symplectic manifolds - symplectic multiplicity and other invariants - Darboux-Givental's theorem - quasi-homogeneous singularities - singularities of planar curves
We study germs of singular varieties in a symplectic space. We introduce the algebraic restrictions of differential forms to singular varieties and prove the generalization of Darboux-Givental' theorem from smooth submanifolds to arbitrary quasi-homogeneous varieties in a symplectic space. Using algebraic restrictions we introduce new symplectic invariants and explain their geometric meaning. We show that a quasi-homogeneous variety $N$ is ...

58K55 ; 32S25 ; 53D05

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Algebraic and Complex Geometry

Let $f$ be a homogeneous polynomial, defining a principal Zariski open set $D(f)$ in some complex projective space $\mathbb{P}^n$ and a Milnor fiber $F(f)$ in the affine space $\mathbb{C}^{n+1}$. Let $f_0, . . . , f_n$ denote the partial derivatives of $f$ with respect to $x_0, . . . , x_n$ and consider syzygies $a_0f_0 + a_1f1 + a_nf_n = 0$, where $a_j$ are homogeneous polynomials of the same degree $k$.
Using the mixed Hodge structure on $D(f)$ and $F(f)$, one can obtain information on the possible values of $k$.
Let $f$ be a homogeneous polynomial, defining a principal Zariski open set $D(f)$ in some complex projective space $\mathbb{P}^n$ and a Milnor fiber $F(f)$ in the affine space $\mathbb{C}^{n+1}$. Let $f_0, . . . , f_n$ denote the partial derivatives of $f$ with respect to $x_0, . . . , x_n$ and consider syzygies $a_0f_0 + a_1f1 + a_nf_n = 0$, where $a_j$ are homogeneous polynomials of the same degree $k$.
Using the mixed Hodge structure on ...

14B05 ; 13D02 ; 32S35

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Algebraic and Complex Geometry

Cohomology jump loci of local systems generalize the Milnor monodromy eigenvalues. We address recent progress on the local and global structure of cohomology jump loci. More generally, given an object with a notion of cohomology theory, how can one describe all its deformations subject to cohomology constraints? We give an answer in terms of differential graded Lie algebra pairs. This is joint work with Botong Wang.

14B05 ; 14F05

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- 134 p.

Localisation : Ouvrage RdC (PICH)

difféomorphisme quasi-périodique de surface # espace analytique # fibration de Milnor # fibration sur le cercle # graphe # plusieurs variables complexes # structure géométrique # théorie des noeuds # topologie de dimension faible # variété de Waldhausen reliée # variété de dimension inférieure

32Sxx ; 55M50 ; 57N10

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