Equivalence of higher torsion invariants

We show that the smooth torsion of bundles of manifolds constructed by Dwyer, Weiss, and Williams satisfies the axioms for higher torsion developed by Igusa. As a consequence we obtain that the smooth Dwyer–Weiss–Williams torsion is proportional to the higher torsion of Igusa and Klein.     

Equivalence invariants for submanifolds of homogeneous spaces

Mathematische Annalen -     

Milnor link invariants and quantum 3-manifold invariants

Let be the 3-manifold invariant of Le, Murakami and Ohtsuki. We show that , where denotes terms of degree , if M is a homology 3-sphere obtained from by surgery on an n-component Brunnian link whose Milnor -invariants of length vanish.?We prove a realization theorem which is a partial converse to the above theorem.?Using the Milnor filtration on links, we define a new bifiltration on the vector space with basis the set of oriented diffeomorphism classes of homology 3-spheres. This includes the Milnor level 2 filtration defined by Ohtsuki. We show that the Milnor level 2 and level 3 filtrations coincide after reindexing. Received: October 23, 1998.     

Differential invariants

This paper summarizes recent results on the number and characterization of differential invariants of transformation groups. Generalizations of theorems due to Ovsiannikov and to M. Green are presented, as well as a new approach to finding bounds on the number of independent differential invariants.Supported in part by NSF Grants DMS 91-16672 and DMS 92-04192.     

Design invariants

This paper generalizes the results of Kohler concerning the construction of t-(v, k, ) designs having a group action. Difference families are defined for arbitrary groups and arbitrary design parameters. Furthermore, the results of Brand and Huffman concerning topological invariants of t=2 designs are generalized to arbitrary values of t.The research in this paper was partially supported by an NTSU Faculty Research Grant (# 35524).     

Finite-order invariants of ornaments

Anornament is a collection of oriented closed curves in a plane, no three of which intersect at the same point. We consider homotopy invariants of ornaments. Thefinite-order invariants of ornaments are a natural analog of the Vassiliev invariants of links. The calculation of them is based on the homological study of the corresponding space of singular objects. We perform the “local” part of these calculations and a part of the “global” one, which allows us to estimate the dimensions of the spaces of invariants of any order. We also construct explicity two large series of such invariants and establish some new algebraic structures in the space of invariants. Translated from Itogi Nauki i Tekhniki, Seriya Sovremennaya Matematika i Ee Prilozheniya. Tematicheskie Obzory. Vol. 35, Algebraicheskaya Geometriya-6, 1996.     

Projective invariants of CR-hypersurfaces

We study the equivalence problem under projective transformation for CR-hypersurfaces of complex projective space. A complete set of projective differential invariants for analytic hypersurfaces is given. The self-dual strongly ?-linearly convex hypersurfaces are characterized.     

Computable Legendrian invariants

We establish tools to facilitate the computation and application of the Chekanov-Eliashberg differential graded algebra (DGA), a Legendrian-isotopy invariant of Legendrian knots and links in standard contact three space. More specifically, we reformulate the DGA in terms of front projections, and introduce the characteristic algebra, a new invariant derived from the DGA. We use our techniques to distinguish between several previously indistinguishable Legendrian knots and links.     

Typical separating invariants

It is shown that a trivial version of polarization is sufficient to produce separating systems of polynomial invariants: If two points in the direct sum of the G-modules W and m copies of V can be separated by polynomial invariants, then they can be separated by invariants depending only on variables of type V; when G is reductive, invariants depending only on variables suffice. A similar result is valid for rational invariants. Explicit bounds on the number of type V variables in a complete system of typical separating invariants are given for the binary polyhedral groups, and this is applied to the invariant theory of binary forms.     

Isomorphisms preserving invariants

Let V and W be finite dimensional real vector spaces and let G ì GL(V){G \subset {\rm GL}(V)} and H ì GL(W){H \subset {\rm GL}(W)} be finite subgroups. Assume for simplicity that the actions contain no reflections. Let Y and Z denote the real algebraic varieties corresponding to \mathbbR[V]^G{\mathbb{R}[V]^G} and \mathbbR[W]^H{\mathbb{R}[W]^H}, respectively. If V and W are quasi-isomorphic, i.e., if there is a linear isomorphism L : V → W such that L sends G-orbits to H-orbits and L ⁻¹ sends H-orbits to G-orbits, then L induces an isomorphism of Y and Z. Conversely, suppose that f : Y → Z is a germ of a diffeomorphism sending the origin of Y to the origin of Z. Then we show that V and W are quasi-isomorphic, This result is closely related to a theorem of Strub [8], for which we give a new proof. We also give a new proof of a result of Kriegl et al. [3] on lifting of biholomorphisms of quotient spaces.     

Ideal Turaev-Viro invariants

Turaev-Viro invariants are defined via state sum polynomials associated to a special spine or a triangulation of a compact 3-manifold. By evaluation of the state sum at any solution of the so-called Biedenharn-Elliott equations, one obtains a homeomorphism invariant of the manifold (“numerical Turaev-Viro invariant”). The Biedenharn-Elliott equations define a polynomial ideal. The key observation of this paper is that the coset of the state sum polynomial with respect to that ideal is a homeomorphism invariant of the manifold (“ideal Turaev-Viro invariant”), stronger than the numerical Turaev-Viro invariants. Using computer algebra, we obtain computational results on several examples of ideal Turaev-Viro invariants, for all closed orientable irreducible manifolds of complexity at most 9.     

Covering Sato-Levine invariants

Two covering versions of the Sato-Levine invariant are constructed which provide obstructions to certain two-component oriented links in the 3-sphere being link concordant to boundary links. These covering invariants are rational functions one of which detects both nonamphicheirality and noninvertibility of oriented links.

     

Connected monomial invariants

We define the monomial invariants of a projective variety Z; they are invariants coming from the generic initial ideal of Z.We prove that, under suitable hypotheses, a variety of codimension at least two has connected monomial invariants; as a corollary, we generalize a result of Cook [C]: if Z is an integral variety of codimension two, satisfying the hypothesis s_Z=s, then its monomial invariants are connected.The authors are members of CNR–GNSAGA (Italy).During the preparation of this paper the authors were partially supported by National Research Project Geometria sulle varietà algebriche COFIN 2002 of MIUR–Italy.Mathematics Subject Classification (2001): 14M07Acknowledgement The authors had fruitful discussions–either in person or via e-mail–on the topics of this paper with many people, among them Matsumi Amasaki, Iustin Coanda, Wolfram Decker, Mark Green, Francesco Russo, Enrico Sbarra, Enrico Schlesinger, Frank Schreyer; their help is gratefully acknowleged. Last, but by no means least, one of the referees pointed out that our original result, Corollary 2.7, could be significantly enlarged in its scope, thus giving Theorem 2.4.     

Generalized Dickson invariants

The action of the Steenrod Algebra on the Dickson invariants is studied in a certain ‘localized’ context. In this context one can define a completed version of the Steenrod Algebra which acts on the local Dickson invariants in a manner which extends the action of the Steenrod Algebra on the usual invariants. One can also construct an infinite Dickson Algebra which carries a left and a right action of the completed Steenrod Algebra and a nondegenerate bilinear form which makes those actions dual. Supported in part by the Alfred P. Sloan Foundation and the Edmund Landau Center for Research in Mathematical Analysis, sponsored by the Minerva Foundation (Germany).