Linking forms, reciprocity for Gauss sums and invariants of 3-manifolds

We study invariants of -manifolds derived from finite abelian groups equipped with quadratic forms. These invariants arise in Turaev's theory of modular categories and generalize those of H. Murakami, T. Ohtsuki and M. Okada. The crucial algebraic tool is a new reciprocity formula for Gauss sums, generalizing classical formulas of Cauchy, Kronecker, Krazer and Siegel. We use this reciprocity formula to give an explicit formula for the invariants and to generalize them to higher dimensions.

     

The triplication formula for Gauss sums

A new proof of the triplication formula for Gauss sums is given. It mimics an old proof of the analogous result for gamma functions. The techniques are formal and rely upon the character properties of fields. A new character sum evaluation is given.     

Computing Turaev-Viro invariants for 3-manifolds

We give a simple surface interpretation for each summand in the evaluation of Turaev-Viro invariants, for the case of small (up to eighth) roots of unity. From this interpretation follows an efficient scheme to compute these invariants. Extensive tables relative to a rich variety of 3-manifolds are explicitly presented.     

Braids and invariants of 3-manifolds

Supported in part by a grant of the NSF and by the Sloan Foundation     

On the general Dedekind sums and its reciprocity formula

In this paper, we prove an interesting reciprocity formula for a certain case of a general Dedekind sums using analytic methods and the Fourier expansion of the Bernoulli polynomials.     

Categorical group invariants of 3-manifolds

For a given class \({\mathcal{G}}\) of groups, a 3-manifold M is of \({\mathcal{G}}\) -category \({\leq k}\) if it can be covered by k open subsets such that for each path-component W of the subsets the image of its fundamental group \({ \pi_1(W) \rightarrow \pi(M )}\) belongs to \({\mathcal{G}}\) . The smallest number k such that M admits such a covering is the \({\mathcal{G}}\) -category, \({cat_{\mathcal{G}}(M)}\) . If M is closed, it has \({\mathcal{G}}\) -category between 1 and 4. We characterize all closed 3-manifolds of \({\mathcal{G}}\) -category 1, 2, and 3 for various classes \({\mathcal{G}}\) .     

Hopf algebras and invariants of 3-manifolds

This paper studies invariants of 3-manifolds derived from finite dimensional Hopf algebras. The invariants are based on right integrals for the Hopf algebras. In fact, it is shown that the defining property of the right integral is an algebraic translation of a necessary condition for invariance under handle slides in the Kirby calculus. The resulting class of invariants is distinct from the class of Witten-Reshetikhin-Turaev invariants.     

The approximate functional formula for the theta function and Diophantine Gauss sums

We consider the polygonal lines in the complex plane whose -th vertex is defined by (with ), where the prime means that the first and last terms in the sum are halved. By introducing the discrete curvature of the polygonal line, and by exploiting the similarity of segments of the line, for small , to Cornu spirals (C-spirals), we prove the precise renormalization formula

where , the nearest integer to and . This formula, which sharpens Hardy and Littlewood's approximate functional formula for the theta function, generalizes to irrationals, as a Diophantine inequality, the well-known sum formula of Gauss. The geometrical meaning of the relation between the two limits is that the first sum is taken to a point of inflection of the corresponding C-spirals. The second sum replaces whole C-spirals of the first by unit vectors times scale and phase factors. The block renormalization procedure implied by this replacement is governed by the circle map

whose orbits are analyzed by expressing as an even continued fraction.

     

L 2-topological invariants of 3-manifolds

Summary We give results on theL ²-Betti numbers and Novikov-Shubin invariants of compact manifolds, especially 3-manifolds. We first study the Betti numbers and Novikov-Shubin invariants of a chain complex of Hilbert modules over a finite von Neumann algebra. We establish inequalities among the Novikov-Shubin invariants of the terms in a short exact sequence of chain complexes. Our algebraic results, along with some analytic results on geometric 3-manifolds, are used to compute theL ²-Betti numbers of compact 3-manifolds which satisfy a weak form of the geometrization conjecture, and to compute or estimate their Novikov-Shubin invariants.Oblatum 6-V-1993 & 20-VI-1994Partially supported by NSF-grant DMS 9101920Partially supported by NSF-grant DMS 9103327     

Pre-Bloch invariants of 3-manifolds with boundary

Let M be an oriented hyperbolic 3-manifold with finite volume. In [W.D. Neumann, J. Yang, Bloch invariants of hyperbolic 3-manifolds, Duke Math. J. 96 (1999) 29-59. [9]], Neumann and Yang defined an element β(M) of Bloch group B(C) for M. For this β(M), volume and Chern-Simons invariant of M is represented by a transcendental function. In this paper, we define β(M,ρ,C,o)∈P(C) for an oriented 3-manifold M with boundary, a representation of its fundamental group , a pants decomposition C of ∂M and an orientation o on simple closed curves of C. Unlike in the case of finite volume, we construct an element of pre-Bloch group P(C), and we need essentially the pants decomposition on the boundary. The volume makes sense for β(M,ρ,C,o) and we can describe the variation of volume on the deformation space.     

A reciprocity formula for quadratic forms

LetQ(x) denote a quadratic form over the rational integers in four variables (x=(x₁,...,x₄)). ThenQ is representable as a symmetric matrix. Assume this matrix to be non-singular modp(p≠2 prime); then the “inverse” quadratic formQ ^?1 modp can be defined. Letf:?⁴→? be defined such that the Fourier transformf exists and the sum $$\sum\limits_{x \in \mathbb{Z}^4 } {f(c x), c \in \mathbb{R}, c \ne 0} $$ is convergent. Furthermore, letm=p ₁...p _k be the product ofk distinct primes withm>1, 2×m; let $$\varepsilon = \prod\limits_{i = 1}^k {\left( {\frac{{\det Q}}{{p_i }}} \right)} \ne 0$$ for the Legendre symbol $$\left( {\frac{ \cdot }{p}} \right)$$ ; define $$B_i (Q,x) = \left\{ {\begin{array}{*{20}c} {1 for Q(x) \equiv 0\bmod p_i } \\ , \\ {0 for Q(x)\not \equiv 0\bmod p_i } \\ \end{array} } \right.$$ and forr∈?,r>0, $$F(Q,f,r) = \sum\limits_{x \in \mathbb{Z}^4 } {\left( {\prod\limits_{i = 1}^k {\left( {B_i (Q,x) - \frac{1}{{p_i }}} \right)} } \right)f(r^{ - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} x)} $$ Then we have $$F(Q,f,m) = \varepsilon F(Q^{ - 1} ,\hat f,m)$$      

Strong integrality of quantum invariants of 3-manifolds

We prove that the quantum -invariant of an arbitrary 3-manifold is always an algebraic integer if the order of the quantum parameter is co-prime with the order of the torsion part of . An even stronger integrality, known as cyclotomic integrality, was established by Habiro for integral homology 3-spheres. Here we also generalize Habiro's result to all rational homology 3-spheres.

     

A formula on Heegaard genus of self-amalgamated 3-manifolds

Let M be an orientable compact irreducible and ∂-irreducible 3-manifold, and suppose ∂M consists of two boundary components F₁ and F₂ with g(F₁)=g(F₂)>1. Let Mf be the closed orientable 3-manifold obtained by identifying F₁ and F₂ via a homeomorphism f:F₁→F₂. With the assumption that M is small or g(M,F₁)=g(M)+g(F₁), we show that if f is sufficiently complicated, then g(Mf)=g(M,∂M)+1.     

Equidistribution of Gauss sums and Kloosterman sums

Let m be a positive integer. Fix a nontrivial additive character for each finite field F_q. To state the first result of this paper, we also fix r distinct multiplicative characters ₁,...,_r for each finite field F_q with more than r elements. We shall prove that when varies over multiplicative characters of F_q other than the m-th roots of the r-tuples of angles of Gauss sums are asymptotically equidistributed on the r-dimensional torus (S¹)^r as q goes to infinity.The n-dimensional Kloosterman sum over F_q at a F_q^× is One can define the angle (q,a) of Kl_n(q,a) in a suitable way. We shall prove that when a varies over nonzero elements of F_q, the q–1 angles (q,a^m) of Kloosterman sums are asymptotically equidistributed as q goes to infinity.Mathematics Subject Classification (2000) 11L05, 14F20