The International Congresses of Mathematicians (ICMs) take place every four years at different locations around the globe, and are the largest regular gatherings of mathematicians from all nations. However, as much as the assembled mathematicians may like to pretend that these gatherings transcend politics, they have always been coloured by world events: the congresses prior to the Second World War saw friction between French and German mathematicians, for example, whilst Cold War political tensions likewise shaped the conduct of later congresses.
Predictions for Roads
Abstract
Road travel is taking longer each year in the UK. This has been true for the last four years. Travel times have increased by 4% in the last two years. Applying the principle finding of the Eddington Report 2006, this change over the last two years will cost the UK economy an additional £2bn per year going forward even without further deterioration. Additional travel times are matched by a greater unreliability of travel times.
Knowing demand and road capacity, can we predict travel times?
We will look briefly at previous partial solutions and the abundance of motorway data in the UK. Can we make a breakthrough to achieve real-time predictions?
Stable twisted cohomology via scanning
Abstract
The technique of scanning, or the parameterised Pontrjagin--Thom construction, has been extraordinarily successful in calculating the cohomology of configuration spaces (McDuff), moduli spaces of Riemann surfaces (Madsen, Tillmann, Weiss), moduli spaces of graphs (Galatius), and moduli spaces of manifolds of higher dimension (Galatius, R-W, Botvinnik, Perlmutter), with constant coefficients. In each case the method also works to study the cohomology of moduli spaces of objects equipped with a "tangential structure". I will explain how choosing an auxiliary highly-symmetric tangential structure often lets one calculate the cohomology of these moduli spaces with large families of twisted coefficients, by exploiting the symmetries of the tangential structure and using a little representation theory.
Operad groups and the homology of the Higman-Thompson groups
Abstract
Markus Szymik and I computed the homology of the Higman-Thompson groups by first showing that they stabilize (with slope 0), and then computing the stable homology. I will in this talk give a new point of view on the computation of the stable homology using Thumann's "operad groups". I will also give an idea of how scanning methods can enter the picture. (This is partially joint work with Søren Galatius.)
Homotopical properties of the diffeomorphism group of a smooth homotopy sphere
Abstract
It is hard to detect the exotic nature of an exotic n-sphere M
in homotopical features of the diffeomorphism group Diff(M). The well
known reason is that Diff(M) contains a big topological subgroup H which
is identified with the group of diffeomorphisms rel boundary of the
n-disk, with a small coset space Diff(M)/H which is invariably homotopy
equivalent to O(n+1). Therefore it seems that our only chance to detect
the exotic nature of M in homotopical features of Diff(M) is to see
something in this extension. (To make sense of "homotopical features of
Diff(M)" one should think of Diff(M) as a space with a multiplication
acting on an n-sphere.) I am planning to report on PhD work of O Sommer
and calculations due to myself and Sommer which, if all goes well, would
show that Diff(M) has some exotic homotopical properties in the case
where M is the 7-dimensional exotic sphere of Kervaire-Milnor fame which
bounds a compact smooth framed 8-manifold of signature 8. The
theoretical work is based on classical smoothing theory and the
calculations would be based on ever-ongoing (>30 years) joint work
Weiss-Williams, and might give me and Williams another valuable
incentive to finish it.
Diffeomorphism-equivariant configuration spaces with twisted summable labels
Abstract
We construct the diffeomorphism-equivariant “scanning map” associated to the configuration spaces of manifolds with twisted summable labels. The scanning map is also functorial with respect to embeddings of manifolds. To adapt P. Salvatore's idea of non-commutative summation into twisted setting, we define a bundle of Fulton-MacPherson operads over a manifold M whose fibres are built within tangent spaces of M.
Surgery on manifolds: the early days
Abstract
In 1956 Milnor published a paper proving that there are manifolds homeomorphic to the 7-sphere but not diffeomorphic to it. Seeking to generalise this example, he was led in around 1960 to introduce a construction for killing homotopy groups of manifolds. When this was generalised to killing relative homotopy groups it became a general and powerful method of construction. An obstruction arises to killing the last group, and the analysis of this obstruction in general leads to a new theory.
15:45
From moduli spaces of manifolds to K-theory
Abstract
For mapping class groups of surfaces it is well-understood that their homology stability is closely related to the fact that they give rise to an infinite loop space. Indeed, they define an operad whose algebras group complete to infinite loop spaces.
In recent work with Basterra, Bobkova, Ponto and Yaekel we define operads with homology stability (OHS) more generally and prove that they are infinite loop space operads in the above sense. The strong homology stability results of Galatius and Randal-Williams for moduli spaces of manifolds can be used to construct examples of OHSs. As a consequence the map to K-theory defined by the action of the diffeomorphisms on the middle dimensional homology can be shown to be a map of infinite loop spaces.
Symmetry-breaking and nonlocal reaction-diffusion mechanisms in bioactive porous media, or "How not to model porous media"
Holographic renormalization and supersymmetry
Abstract
Localization and holography are powerful approaches to the computation of supersymmetric observables. The computations may, however, include divergences. Therefore, one needs renormalization schemes preserving supersymmetry. I will consider minimal gauged supergravity in five dimensions to demonstrate that the standard holographic renormalization scheme breaks supersymmetry, and propose a set of non-standard boundary counterterms that restore supersymmetry. I will then show that for a certain class of solutions the improved on-shell action correctly reproduces an intrinsic observable of four-dimensional SCFTs, the supersymmetric Casimir energy.