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Series: Geometry Topology Seminar

In a recent conjecture by Tian Yang and Qingtao Chen, it has been observedthat the log of Turaev-Viro invariants of 3-manifolds at a special root ofunity grow proportionnally to the level times hyperbolic volume of themanifold, as in the usual volume conjecture for the colored Jonespolynomial.In the case of link complements, we derive a formula to expressTuraev-Viro invariants as a sum of values of colored Jones polynomial, andget a proof of Yang and Chen's conjecture for a few link complements. Theformula also raises new questions about the asymptotics of colored Jonespolynomials. Joint with Effie Kalfagianni and Tian Yang.

Series: Geometry Topology Seminar

The point-pushing subgroup of the mapping class group of a surface with a marked point can be considered topologically as the subgroup
that pushes the marked point about loops in the surface. Birman demonstrated that this subgroup is abstractly isomorphic to the fundamental
group of the surface, \pi_1(S). We can characterize this point-pushing subgroup algebraically as the only normal subgroup inside of the mapping
class group isomorphic to \pi_1(S). This uniqueness allows us to recover a description of the outer automorphism group of the mapping class group.

Series: Geometry Topology Seminar

Series: Geometry Topology Seminar

Dehn surgery is a fundamental tool for constructing oriented 3-Manifolds. If we fix a knot K in an oriented 3-manifold Y and do surgeries with distinct slopes r and s, we can ask under which conditions the resulting oriented manifold Y(r) and Y(s) might be orientation preserving homeomorphic. The cosmetic surgery conjecture state that if the knot exterior is boundary irreducible then this can't happen. My talk will be about the case where Y is an homology sphere and K is an hyperbolic knot.

Series: Geometry Topology Seminar

The Grothendieck group K_0 of a commutative ring is well-known to be a \lambda-ring: although the exterior powers are non-additive, they induce maps on K_0 satisfying various universal identities. The \lambda-operations are known to give homomorphisms on higher K-groups. In joint work in progress with Barwick, Glasman, and Nikolaus, we give a general framework for such operations. Namely, we show that the K-theory space is naturally functorial with respect to polynomial functors, and describe a universal property of the extended K-theory functor. This extends an earlier algebraic result of Dold for K_0.

Series: Geometry Topology Seminar

The Drinfeld double of a finite dimensional Hopf algebra is a
quasi-triangular Hopf algebra with the canonical element as the universal R
matrix, and we obtain a ribbon Hopf algebra by adding the ribbon element.
The universal quantum invariant is an invariant of framed links, and is
constructed diagrammatically using a ribbon Hopf algebra. In that
construction, a copy of the universal R matrix is attached to each positive
crossing, and invariance under the Reidemeister III move is shown by the
quantum Yang-Baxter equation of the universal R matrix.
On the other hand, R. Kashaev showed that the Heisenberg double has the
canonical element (the universal S matrix) satisfying the pentagon
relation. In this talk we reconstruct the universal quantum invariant using
Heisenberg double, and extend it to an invariant of colored ideal
triangulations of the complement. In this construction, a copy of the
universal S matrix is attached to each tetrahedron and the invariance under
the colored Pachner (2,3) move is shown by the pentagon equation of the
universal S matrix

Series: Geometry Topology Seminar

The Homfly skein algebra of a surface is defined using links in
thickened surfaces modulo local "skein" relations. It was shown by
Turaev that this quantizes the Goldman symplectic structure on the
character varieties of the surface. In this talk we give a complete
description of this algebra for the torus. We also show it is
isomorphic to the elliptic Hall algebra of Burban and Schiffmann,
which is an algebra whose elements are (formal sums of) sheaves on an
elliptic curve, with multiplication defined by counting extensions of
such sheaves. (Joint work with H. Morton.)

Series: Geometry Topology Seminar

We are going to discuss one of the open problems of geometric tomography about projections. Along with partial previous results, the proof of the problem below will be investigated.Let $2\le k\le d-1$ and let $P$ and $Q$ be two convex polytopes in ${\mathbb E^d}$. Assume that their projections, $P|H$, $Q|H$, onto every $k$-dimensional subspace $H$, are congruent. We will show that $P$ and $Q$ or $P$ and $-Q$ are translates of each other. If the time permits, we also will discuss an analogous result for sections by showing that $P=Q$ or $P=-Q$, provided the polytopes contain the origin in their interior and their sections, $P \cap H$, $Q \cap H$, by every $k$-dimensional subspace $H$, are congruent.

Series: Geometry Topology Seminar

We discuss a few applications of Pin(2)-monopole Floer homology to problems in homology cobordism. Our main protagonists are (connected sums of) homology spheres obtained by surgery on alternating and L-space knots with Arf invariant zero.

Series: Geometry Topology Seminar

Khovanov homology is a powerful and computable homology theory for links which extends to tangles and tangle cobordisms. It is closely, but perhaps mysteriously, related to many flavors of Floer homology. Szabó has constructed a combinatorial spectral sequence from Khovanov homology which (conjecturally) converges to a Heegaard Floer-theoretic object. We will discuss work in progress to extend Szabó’s construction to an invariant of tangles and surfaces in the four-sphere.