Ninety Third Meeting of the
Transpennine Topology Triangle

School of Mathematics and Statistics

University of Leicester

Wednesday 12th November 2014

Supported by the London Mathematical Society 

Everyone who wishes to participate is welcome, particularly postgraduate students. We'll operate the usual criteria for assistance with travel expenses. Beneficiaries will need to complete the standard forms, available from the TTT Homepage.


11:15 – 12:00
College House Ground Floor Study Area

Tea, Coffee and Biscuits

12:00 – 13:00 


James Griffin

Moduli spaces of labelled graphs

Although Aut(Fr) has a finite simplicial set as a classifying space, its homology is extremely difficult to calculate and the problem just gets worse as the rank r increases.  However by a result of Hatcher and Vogtmann the homology is known to be stable, and Galatius computed this stable homology to be that of the sphere spectrum.  More generally Hatcher and Wahl conjectured that automorphism groups Aut(H*G*...*G) of free products of groups are homologically stable. I'll prove this via a moduli space of labelled graphs and a little category theory.

14:30 – 15:30 


(note room change)

Sarah Whitehouse
(note change of speaker)

Binomial rings in topology

A binomial ring is a torsion-free commutative ring that is closed under the binomial operations r(r-1)...(r-n+1)/n! for all positive integers n. They were first introduced by Hall around 1969 and they are related to integer-valued polynomials, Witt vectors and lambda-rings. I will discuss properties of these rings and explain how some interesting examples arise in topology.

(This is a last minute change to the programme.)

15:30 – 16:00

Bennett Foyer

Tea, Coffee and Biscuits
16:00 –17:00

Jeff Giansiracusa
Variations on a theme - ribbon graphs, topological conformal field theories and Hochschild homology

Costello used a ribbon graph model of the moduli space of Riemann surfaces to show that open topological conformal field theories are equivalent to A-infinity categories, and that such a theory has a universal extension to an open-closed theory whose closed state space is the Hochschild chains on the open part.  I will explain how this picture generalizes to unoriented surfaces, and surfaces equipped with principle G-bundles, among other structures.  In the unoriented case, this is joint work with Ramses Fernandez Valencia; Mobius graphs and an involutive variant of Hochschild homology appear.

There are various places for lunch - follow a group of locals if in doubt.

A group is likely to be going for drinks and an early dinner after the last talk - all are welcome to join.