On ohtsuki’s invariants of integral homology 3-spheres

We provide some more explicit formulae to facilitate the computation of Ohtsuki’s rational invariants λ _n of integral homology 3-spheres extracted from Reshetikhin-TuraevSU(2) quantum invariants. Several interesting consequences will follow from our computation of λ₂. One of them says that λ₂ is always an integer divisible by 3. It seems interesting to compare this result with the fact shown by Murakami that λ₁ is 6 times the Casson invariant. Other consequences include some general criteria for distinguishing homology 3-spheres obtained from surgery on knots by using the Jones polynomial. The first author is supported in part by NSF and the second author is supported by an NSF Postdoctoral Fellowship.     

Trivial cocycles and invariants of homology 3-spheres

We study the relationship between trivial cocycles on the Torelli group and invariants of oriented integral homology 3-spheres. We apply this study to give a new purely algebraic construction of the Casson invariant. As a by-product we get a new 2-torsion cohomology class in the second integral cohomology of the Torelli group.     

A perturbative SU(3) Casson invariant

A perturbative SU(3) Casson invariant for integral homology 3-sphere is defined. Besides being fully perturbative, it has the nice properties: (1) is an integer. (2) It is preserved under orientation change. (3) A connect sum formula. Explicit calculations of the invariant for 1/k surgery of (2, q) torus knot are presented and compared with Boden-Herald‚s different SU(3) generalization of Casson‚s invariant. For those cases computed, the invariant defined here is a quadratic polynomial in k for k > 0 and a different quadratic polynomial for k < 0. Received: October 12, 2000     

Knot theory and the Casson invariant in Artin presentation theory

In Artin presentation theory, a smooth, compact four-manifold is determined by a certain type of presentation of the fundamental group of its boundary. Topological invariants of both three-and four-manifolds can be calculated solely in terms of functions of the discrete Artin presentation. González-Acuña proposed such a formula for the Rokhlin invariant of an integral homology three-sphere. This paper provides a formula for the Casson invariant of rational homology spheres. Thus, all 3D Seiberg-Witten invariants can be calculated by using methods of the theory of groups in Artin presentation theory. The Casson invariant is closely related to canonical knots determined by an Artin presentation. It is also shown that any knot in any three-manifold appears as a canonical knot in Artin presentation theory. An open problem is to determine 4D Seiberg-Witten and Donaldson invariants in Artin presentation theory.     

Lattice Points Inside Rational Simplices and the Casson Invariant of Brieskorn Spheres

We express the number of lattice points inside certain simplices with vertices in Q³ or Q⁴ in terms of Dedekind–Rademacher sums. This leads to an elementary proof of a formula relating the Euler characteristic of the Seiberg–Witten-Floer homology of a Brieskorn Z-homology sphere to the Casson invariant.     

Invariant sets and measures of nonexpansive group automorphisms

We write a formula for the LMO invariant of a rational homology sphere presented as a rational surgery on a link inS ³. Our main tool is a careful use of the Århus integral and the (now proven) “Wheels” and “Wheeling” conjectures of B-N, Garoufalidis, Rozansky and Thurston. As steps, side benefits and asides we give explicit formulas for the values of the Kontsevich integral on the Hopf link and on Hopf chains, and for the LMO invariant of lens spaces and Seifert fibered spaces. We find that the LMO invariant does not separate lens spaces, is far from separating general Seifert fibered spaces, but does separate Seifert fibered spaces which are integral homology spheres.     

Finite type 3-manifold invariants and the structure of the Torelli group. I

Using the recently developed theory of finite type invariants of integral homology 3-spheres we study the structure of the Torelli group of a closed surface. Explicitly, we construct (a) natural cocycles of the Torelli group (with coefficients in a space of trivalent graphs) and cohomology classes of the abelianized Torelli group; (b) group homomorphisms that detect (rationally) the nontriviality of the lower central series of the Torelli group. Our results are motivated by the appearance of trivalent graphs in topology and in representation theory and the dual role played by the Casson invariant in the theory of finite type invariants of integral homology 3-spheres and in Morita's study [Mo2, Mo3] of the structure of the Torelli group. Our results generalize those of S. Morita [Mo2, Mo3] and complement the recent calculation, due to R. Hain [Ha2], of the I-adic completion of the rational group ring of the Torelli group. We also give analogous results for two other subgroups of the mapping class group. Oblatum 19-IX-1996 & 13-V-1997     

On denominators of the Kontsevich integral and the universal perturbative invariant of 3-manifolds

 The integrality of the Kontsevich integral and perturbative invariants is discussed. It is shown that the denominator of the degree n part of the Kontsevich integral of any knot or link is a divisor of (2!3!…n!)⁴(n+1)!. We prove this by establishing the existence of a Drinfeld's associator in the space of chord diagrams with special denominators. We also show that the denominator of the degree n part of the universal perturbative invariant of homology 3-spheres is not divisible by any prime greater than 2n+1. Oblatum 20-VI-1997 & 28-IV-1998 / Published online: 12 November 1998     

The Chern-Simons invariants of cone-manifolds with Whitehead link singular set

In the present article, we obtain some explicit integral formulas for the generalized Chern-Simons function I(W(α,β)) for Whitehead link cone-manifolds in the hyperbolic and spherical cases. We also give the Chern-Simons invariant for the Whitehead link orbifolds. We find a formula for the Chern-Simons invariant of n-fold coverings of the three-sphere branched over the Whitehead link.     

Une nouvelle définition de l'invariant de CassonA new definition of the Casson invariant

In [4], following [2], we have defined an invariant $\text{Δ(f)∈}\text{Q}$, for any $\text{f∈}\text{M}{}_{\mathrm{g,1}}$, the mapping class group of a compact, connected, oriented surface with connected boundary, genus g. For $\text{f∈}\text{T}{}_{\mathrm{g,1}}$ (a certain subgroup of the Torelli group), we have shown in [4], using Casson surgery formula, that Δ(f) co??ncides with the Casson invariant [1] of the homology sphere M_f, obtained by gluing two handlebodies along f. The purpose of this Note is to prove directly (i.e., without reference to Casson) that Δ(f), for $\text{f∈}\text{T}{}_{\mathrm{g,1}}$, depends only on M_f. The surgery formula, which is a difficult point in Casson version, follows almost immediatly from the definition of Δ(f). To cite this article: B. Perron, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 199–204.     

Encomplexed Brown invariant of real algebraic surfaces in ℝP 3

We construct an invariant of parametrized generic real algebraic surfaces in ?P ³ which generalizes the Brown invariant of immersed surfaces from smooth topology. The invariant is constructed using self-intersections, which are real algebraic curves with points of three local characters: the intersection of two real sheets, the intersection of two complex conjugate sheets or a Whitney umbrella. In Kirby and Melvin (Local surgery formulas for quantum invariants and the Arf invariant, in Proceedings of the Casson Fest, Geom. Topol. Monogr. 7, pp. 213–233, Geom. Topol. Publ., Coventry, 2004) the Brown invariant was expressed through a self-linking number of the self-intersection. We extend the definition of this self-linking number to the case of parametrized generic real algebraic surfaces.     

Convergence of the Newton--Kantorovich Method for Calculating Invariant Subspaces

We propose a version of the Newton--Kantorovich method which, given a nondegenerate square n X n matrix and a number m<n, allows us to calculate the invariant subspace corresponding to its smallest (in modulus) eigenvalues. We obtain estimates of the rate of convergence via an integral criterion for circular dichotomy.     

Vector Hamiltonians in Nambu Mechanics

We give a generalization of the Nambu mechanics based on vector Hamiltonians theory. It is shown that any divergence-free phase flow in ? ⁿ can be represented as a generalized Nambu mechanics with n ? 1 integral invariants. For the case when the phase flow in ? ⁿ has n ? 3 or less first integrals, we introduce the Cartan concept of mechanics. As an example we give the fifth integral invariant of Euler top.     

Transversality for equivariant exact 1-forms and gauge theory on 3-manifolds

An equivariant jet transversality framework is developed for the study of critical sets of invariant functions on G manifolds. Techniques are developed to extend transversality results to the infinite dimensional Fredholm setting. As an application, the generic structure of the SU(4) perturbed flat moduli space of an integral homology three-sphere is described, as well as the generic structure of the parameterized moduli space for a path of perturbations. A similar analysis of the U(3) moduli space for rational homology three-spheres is also carried out.     

The Alexander polynomial and finite type 3-manifold invariants

Using elementary counting methods, we calculate a universal perturbative invariant (also known as the LMO invariant) of a 3-manifold M, satisfying , in terms of the Alexander polynomial of M. We show that +1 surgery on a knot in the 3-sphere induces an injective map from finite type invariants of integral homology 3-spheres to finite type invariants of knots. We also show that weight systems of degree 2m on knots, obtained by applying finite type 3m invariants of integral homology 3-spheres, lie in the algebra of Alexander-Conway weight systems, thus answering the questions raised in [Ga]. Received: 27 April 1998 / in final form: 8 August 1999     

The Euler-Jacobi-Lie integrability theorem

This paper addresses a class of problems associated with the conditions for exact integrability of systems of ordinary differential equations expressed in terms of the properties of tensor invariants. The general theorem of integrability of the system of n differential equations is proved, which admits n ? 2 independent symmetry fields and an invariant volume n-form (integral invariant). General results are applied to the study of steady motions of a continuum with infinite conductivity.     

Khovanov homology of torus links

In this paper we show that there is a cut-off in the Khovanov homology of (2k,2kn)-torus links, namely that the maximal homological degree of non-zero homology groups of (2k,2kn)-torus links is 2k²n. Furthermore, we calculate explicitly the homology group in homological degree 2k²n and prove that it coincides with the center of the ring Hk of crossingless matchings, introduced by M. Khovanov in [M. Khovanov, A functor-valued invariant for tangles, Algebr. Geom. Topol. 2 (2002) 665-741, arXiv:math.QA/0103190]. This gives the proof of part of a conjecture by M. Khovanov and L. Rozansky in [M. Khovanov, L. Rozansky, A homology theory for links in S²×S¹, in preparation]. Also we give an explicit formula for the ranks of the homology groups of (3,n)-torus knots for every n∈N.     

Three-manifold invariants associated with restricted quantum groups

We show a simple relation between Witten–Reshetikhin–Turaev SU(2) invariant and the Hennings invariant associated with the restricted quantum ${{\mathfrak{sl}_{2}}}$ . These invariants are defined in very different methods: the former uses the representation theory of quantum ${{\mathfrak{sl}_{2}}}$ while the latter uses the integral of the Hopf algebra. But they turn out to be the same for most rational homology 3-spheres up to a sign. This relation can be used to prove the integrality of the former invariant.     

On the existence of invariant tori in nearly-integrable Hamiltonian systems with finitely differentiable perturbations

We prove the existence of invariant tori in Hamiltonian systems, which are analytic and integrable except a 2n-times continuously differentiable perturbation (n denotes the number of the degrees of freedom), provided that the moduli of continuity of the 2n-th partial derivatives of the perturbation satisfy a condition of finiteness (condition on an integral), which is more general than a Hölder condition. So far the existence of invariant tori could be proven only under the condition that the 2n-th partial derivatives of the perturbation are Hölder continuous.     

Torsion in the matching complex and chessboard complex

Topological properties of the matching complex were first studied by Bouc in connection with Quillen complexes, and topological properties of the chessboard complex were first studied by Garst in connection with Tits coset complexes. Björner, Lovász, Vre?ica and ?ivaljevi? established bounds on the connectivity of these complexes and conjectured that these bounds are sharp. In this paper we show that the conjecture is true by establishing the nonvanishing of integral homology in the degrees given by these bounds. Moreover, we show that for sufficiently large n, the bottom nonvanishing homology of the matching complex Mn is an elementary 3-group, improving a result of Bouc, and that the bottom nonvanishing homology of the chessboard complex Mn,n is a 3-group of exponent at most 9. When , the bottom nonvanishing homology of Mn,n is shown to be Z₃. Our proofs rely on computer calculations, long exact sequences, representation theory, and tableau combinatorics.