arXiv subjects

Jens Lieberum

Publications and source records attributed to Jens Lieberum.

6 recordsLinked to original sources

arXiv2002

The Drinfeld associator of gl(1|1)

We determine explicitly a rational even Drinfeld associator Q in a completion of the universal enveloping algebra of the Lie superalgebra gl(1|1)^3. More generally, we define a new algebra of trivalent diagrams that has a unique even horizontal group-like Drinfeld associator P. The associator P is mapped to Q by a weight system. As a result of independent interest, we show how O. Viro's generalization Delta^1 of the multi-variable Alexander polynomial can be obtained from the universal Vassiliev invariant of trivalent graphs. We determine P by using the invariant Delta^1(T) of a planar tetrahedron T.

math.QA↗

arXiv2001

Universal Vassiliev invariants of links in coverings of 3-manifolds

We study Vassiliev invariants of links in a 3-manifold $M$ by using chord diagrams labeled by elements of the fundamental group of $M$. We construct universal Vassiliev invariants of links in $M$, where $M=P^2\times [0,1]$ is a cylinder over the real projective plane $P^2$, $M=Σ\times [0,1]$ is a cylinder over a surface $Σ$ with boundary, and $M=S^1\times S^2$. A finite covering $p:N\longrightarrow M$ induces a map $π_1(p)^*$ between labeled chord diagrams that corresponds to taking the preimage $p^{-1}(L)\subset N$ of a link $L\subset M$. The maps $p^{-1}$ and $π_1(p)^*$ intertwine the constructed universal Vassiliev invariants.

math.QA↗

arXiv2000

Skein modules of links in cylinders over surfaces

We define the Conway skein module C(M) of ordered based links in a 3-manifold M. This module gives rise to C(M)-valued invariants of usual links in M. We determine a basis of the Z[z]-module C(F x [0,1])/Tor(C(F x [0,1])) where F is the real projective plane or a surface with boundary. For cylinders over the Moebius strip or the projective plane we derive special properties of the Conway skein module, including a refinement of a theorem of Kawauchi and Hartley about the Conway polynomial of strongly positive amphicheiral knots in S^3. We also determine the Homfly and Kauffman skein modules of F x [0,1] where F is an oriented surface with boundary.

math.QA↗

arXiv2000

The LMO-invariant of 3-manifolds of rank one and the Alexander polynomial

We prove that the LMO-invariant of a 3-manifold of rank one is determined by the Alexander polynomial of the manifold, and conversely, that the Alexander polynomial is determined by the LMO-invariant. Furthermore, we show that the Alexander polynomial of a null-homologous knot in a rational homology 3-sphere can be obtained by composing the weight system of the Alexander polynomial with the Aarhus invariant of knots.

math.QA↗

arXiv2000

On Vassiliev Invariants not Coming from Semisimple Lie Algebras

We prove a refinement of Vogel's statement that the Vassiliev invariants of knots coming from semisimple Lie algebras do not generate all Vassiliev invariants. This refinement takes into account the second grading on Vassiliev invariants induced by cabling of knots. As an application we get an amelioration of the actually known lower bounds for the dimensions of the space of Vassiliev invariants.

q-alg↗

arXiv1997

Chromatic weight systems and the corresponding knot invariants

This paper contains a proof that chromatic weight systems, introduced by Chmutov, Duzhin and Lando, can be expressed in terms of weight systems associated with direct sums of the Lie algebras gl_n and so_n. As a consequence the Vassiliev invariants of knots corresponding to the chromatic weight systems distinguish exactly the same knots as a one variable specialisation Y of the Homfly and Kauffman polynomial.

q-alg↗