The vanishing Euler characteristic of an isolated determinantal singularity

Let (X, 0) be a complex analytic isolated determinantal singularity. We will define the vanishing Euler characteristic of (X, 0) and the Milnor number of a holomorphic function germ with an isolated singularity on X, f: (X, 0) → ?.     

Milnor open books and Milnor fillable contact 3-manifolds

We say that an oriented contact manifold (M,ξ) is Milnor fillable if it is contactomorphic to the contact boundary of an isolated complex-analytic singularity (X,x). In this article we prove that any three-dimensional oriented manifold admits at most one Milnor fillable contact structure up to contactomorphism. The proof is based on Milnor open books: we associate an open book decomposition of M with any holomorphic function f:(X,x)→(C,0), with isolated singularity at x and we verify that all these open books carry the contact structure ξ of (M,ξ)—generalizing results of Milnor and Giroux.     

Sur le nombre de Milnor d'une singularité semi-quasi-homogèneAbout the Milnor number of a semi-quasi-homogeneous singularity

Let f=(f₁,…,f_p) be a semi-quasi-homogeneous family of holomorphic functions in a neighborhood of the origin in $\text{C}{}^{\mathrm{n}}$. We prove that f defines an isolated complete intersection singularity, and we express the Milnor number of this singularity as the colength of an ideal naturally associated to f. This generalizes a formula due to G.M. Greuel. To cite this article: J. Briançon, H. Maynadier-Gervais, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 317–320.     

Limits of tangents and minimality of complex links

We show that the complex link of a large class of space germs (X,x₀) is characterized by its “simplicity”, among the Milnor fibres of functions with isolated singularity on X. This amounts to the minimality of the Milnor number, whenever this number is defined. Such a phenomenon has been first pointed out in case (X,x₀) is an isolated hypersurface singularity, by Teissier (Cycles évanescents, sections planes et conditions de Whitney, in: Singularités à Cargèse 1972, Asterisque, Nos. 7 et 8, Soc. Math. France, Paris, 1973, pp. 285-362).     

The Euler obstruction of a function on a determinantal variety and on a curve

Given an analytic function germ f: (X, 0) → C on an isolated determinantal singularity or on a reduced curve, we present formulas relating the local Euler obstruction of f to the vanishing Euler characteristic of the fiber X ∩ f^-1(0) and to the Milnor number of f. Restricting ourselves to the case where X is a complete intersection, we obtain an easy way to calculate the local Euler obstruction of f as the difference between the dimension of two algebras.     

A bound for the Milnor number of plane curve singularities

Let f = 0 be a plane algebraic curve of degree d > 1 with an isolated singular point at 0 ∈ ?². We show that the Milnor number μ₀(f) is less than or equal to (d?1)² ? [d/2], unless f = 0 is a set of d concurrent lines passing through 0, and characterize the curves f = 0 for which μ₀(f) = (d?1)² ? [d/2].     

The boundary of the Milnor fibre of certain non-isolated singularities

Let \( \Phi : (\mathbb {C}^2, 0) \rightarrow ( \mathbb {C}^3, 0) \) be a finitely determined complex analytic germ and let \((\{f=0\},0)\) be the reduced equation of its image, a non-isolated hypersurface singularity. We provide the plumbing graph of the boundary of the Milnor fibre of f from the double-point-geometry of \(\Phi \).     

Real Milnor Fibrations and (C)-Regularity

In this paper we study Milnor fibrations associated to real isolated singularities defined by map-germs f: (^m,0)(²,0). The main result relates the existence of the Milnor fibration with the (C)-regularity of the family of hypersurfaces with isolated singularity obtained by projecting f into the family L_– of all lines through the origin in the plane ².     

Motivic Milnor fibers of a rational function

Let P and Q be two complex polynomials and f be the induced rational function. In this Note we define a motivic Milnor fiber of the germ of f at an indeterminacy point x for a value a, a motivic Milnor fiber of f for a value a and finally motivic bifurcation sets.     

Picard-Lefschetz monodromy of products

Let f and g be reduced homogeneous polynomials in separate sets of variables. We establish a simple formula that relates the eigenspace decomposition of the monodromy operator on the Milnor fiber cohomology of fg to that of f and g separately. We use a relation between local systems and Milnor fiber cohomology that has been established by D. Cohen and A. Suciu.     

Non-trivial simple poles at negative integers and mass concentration at singularity

Let (X,0) be the germ of a normal space of dimension n+1 and let f be the germ at 0 of a holomorphic function on X. Assume both X and f have an isolated singularity at 0. Denote by J the image of the restriction map , where F is the Milnor fibre of f at 0. We prove that the canonical Hermitian form on , given by poles of order at in the meromorphic extension of , passes to the quotient by J and is non-degenerate on . We show that any non-zero element in J produces a “mass concentration” at the singularity which is related to a simple pole concentrated at for (in a non-na?ve sense). We conclude with an application to the asymptotic expansion of oscillatory integrals , for , when . Received: 28 May 2001 / Published online: 26 April 2002     

The Milnor number of a function on a space curve germ

Given a finite function germ f:(X, 0) (, 0) on a reduced spacecurve singularity (X, 0), we show that µ(f) = µ(X,0) + deg(f) – 1. Here, µ(f) and µ(X, 0) denotethe Milnor numbers of the function and the curve, respectively,and deg(f) is the degree of f. We use this formula to obtainseveral consequences related to the topological triviality andWhitney equisingularity of families of curves and families offunctions on curves.     

The Lê varieties,I

Summary For a complex polynomial,f:( ⁿ⁺¹ ,0) (, 0), with a singular set of complex, dimensions at the origin, we define a sequence of varieties—the Lê varieties, _f ^(k) , off at 0. The multiplicities of these varieties, _f ^(k) , generalize the Milnor number for an isolated singularity. In particular, we show that ifsn-2, the Milnor, fibre off is obtained fromB ²ⁿ by successively attaching _f ^{(n – k)} k-handles, wheren-skn Ifs=n-1, the Milnor fibre off is obtained from a2n-manifold with the homotopy type of a bouquet of _f ^{(n – 1)} circles by successively attaching _f ^{(n – k)} k-handles, where 2kn.The author is a National Science Foundation, Postdoctoral Research Fellow supported by grant # DMS-8807216     

Finite determinacy and Whitney equisingularity of map germs from {\mathbb{C}^n} to {\mathbb{C}^{2n-1}}

We show that a holomorphic map germ ${f : (\mathbb{C}^n,0)\to(\mathbb{C}^{2n-1},0)}$ is finitely determined if and only if the double point scheme D(f) is a reduced curve. If n ≥ 3, we have that μ(D ²(f)) = 2μ(D ²(f)/S ₂)+C(f)?1, where D ²(f) is the lifting of the double point curve in ${(\mathbb{C}^n\times \mathbb{C}^n,0)}$ , μ(X) denotes the Milnor number of X and C(f) is the number of cross-caps that appear in a stable deformation of f. Moreover, we consider an unfolding F(t, x) = (t, f _t (x)) of f and show that if F is μ-constant, then it is excellent in the sense of Gaffney. Finally, we find a minimal set of invariants whose constancy in the family f _t is equivalent to the Whitney equisingularity of F. We also give an example of an unfolding which is topologically trivial, but it is not Whitney equisingular.     

On nonisolated hypersurface singularities

We study germs of holomorphic functions whose singular sets are hypersurfaces with isolated singularity in the cases where the transversal singularity is A ₁. For these singularities, we completely describe the homotopy structure of the Milnor fibers. Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 59, Algebra and Geometry, 2008.     

Localisation des résidus de Baum-Bott, courbes généralisées et K-théorie (I: feuilletages dans \Bbb C2 {\Bbb C}^2 )

Let v be a holomorphic vector field in a neighborhood of a point m ₀ in , which is a non dicritical isolated singularity. Let f = 0 be a reduced equation of the maximal separatrix V through m ₀, v _f the vector field , and the union of separatrices and pseudo-separatrices (i.e. the set of points where v and v _f are colinear). Assuming the foliations defined by v and v _f to be distinct, we prove that the Baum-Bott residue BB(c ₁ ² , v) of v at m ₀, as well as the difference PH(v) - μ between the Poincaré-Hopf index and the Milnor number of V at m ₀, are "localised" near the separatrices and pseudo-separatrices. (The particular case of generalized curves has already been studied in details in [CLS] and [Br]). We also interpret in K-theory the difference PH - μ as well as the GSV index of Gomez Mont-Seade-Verjovski, and we give a caracterisation of generalized curves in this framework, which will enable us to extend this concept in higher dimension. Received: August 25, 2000     

On the duality theorem on an analytic variety

The duality theorem for Coleff–Herrera products on a complex manifold says that if f =  (f ₁, . . . , f _p ) defines a complete intersection, then the annihilator of the Coleff–Herrera product μ ^f equals (locally) the ideal generated by f. This does not hold unrestrictedly on an analytic variety Z. We give necessary, and in many cases sufficient conditions for when the duality theorem holds. These conditions are related to how the zero set of f intersects certain singularity subvarieties of the sheaf ${\mathcal O_Z}$ .     

On splice quotients of the form {zn = f(x,y)}

The splice quotients, defined by W. D. Neumann and J. Wahl, are an interesting class of normal surface singularities with rational homology sphere links. In general, it is difficult to determine whether or not a singularity is analytically isomorphic to a splice quotient, although there are certain necessary topological conditions. Let {zⁿ = f(x, y)} define a surface X_{f, n} with an isolated singularity at the origin in $\mathbb {C}^3$. We show that for irreducible f, if (X_{f, n}, 0) satisfies the necessary topological conditions, then there exists a splice quotient of the form (X_{g, n}, 0), where the plane curve singularity defined by g = 0 has the same topological type as the one defined by f = 0. We also present an example of an (X_{f, n}, 0) that is not a splice quotient, but for which the universal abelian cover is a complete intersection of splice type together with a non‐diagonal action of the discriminant group. © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

On Trajectories of Analytic Gradient Vector Fields

Let f:Rⁿ,0→R,0 be an analytic function defined in a neighbourhood of the origin, having a critical point at 0. We show that the set of non-trivial trajectories of the equation xdot;=∇f(x) attracted by the origin has the same ?ech-Alexander cohomology groups as the real Milnor fibre of f.