The 2-loop polynomial of a knot is a polynomial characterizing the 2-loop part of the Kontsevich invariant of the knot. An aim of this paper is to give a methodology to calculate the 2-loop polynomial. We introduce Gaussian diagrams to calculate the rational version of the Aarhus integral explicitly, which constructs the 2-loop polynomial, and we develop methodology of calculating Gaussian diagrams showing many basic formulas of them. As a consequence, we obtain an explicit presentation of the 2-loop polynomial for knots of genus 1 in terms of derivatives of the Jones polynomial of the knots.Corresponding to quantum and related invariants of 3-manifolds, we can formulate equivariant invariants of the infinite cyclic covers of knots complements. Among such equivariant invariants, we can regard the 2-loop polynomial of a knot as an "equivariant Casson invariant" of the infinite cyclic cover of the knot complement. As an aspect of an equivariant Casson invariant, we show that the 2-loop polynomial of a knot is presented by using finite type invariants of degree Ä 3 of a spine of a Seifert surface of the knot. By calculating this presentation concretely, we show that the degree of the 2-loop polynomial of a knot is bounded by twice the genus of the knot. This estimate of genus is effective, in particular, for knots with trivial Alexander polynomial, such as the Kinoshita-Terasaka knot and the Conway knot.
57M27; 57M25Dedicated to Professor Yukio Matsumoto on the occasion of his 60th birthday
IntroductionThe Kontsevich invariant is a very strong invariant of knots, which dominates all quantum invariants and all Vassiliev invariants, and it is expected that the Kontsevich invariant classifies knots. A problem when we study the Kontsevich invariant is that it is difficult to calculate the Kontsevich invariant for any knot concretely. That is, the value of the Kontsevich invariant is presented by an infinite linear sum of Jacobi diagrams (a certain kind of uni-trivalent graphs), and it is not known so far how to calculate all terms of such a linear sum at the same time for an arbitrarily given knot. Geometry & Topology, Volume 11 (2007) On the 2-loop polynomial of knots
1359by the equivariant linking number (Kojima and Yamasaki [17]) and equivariant finite type invariants of degree Ä 3, while a surgery formula for the Alexander polynomial is given by the equivariant linking number. Another aspect of an equivariant Casson invariant is that the 2-loop polynomial of a knot is presented by using finite type invariants of degree Ä 3 of a spine of a Seifert surface of the knot (Theorem 4.4), while the Alexander polynomial of a knot is presented by using finite type invariants of degree 1, ie, the Seifert form, of a spine of a Seifert surface of the knot.By constructing the 2-loop polynomial using Gaussian diagrams along the latter aspect, in Theorem 4.7, we show the following estimate, which was conjectured by Rozansky [40], that the degree of the 2-loop polynomial of a knot Ä 2 the genus of the knot ;where the genus of a kno...