University of Sheffield

Wednesday, July 11th 2001

This will be a working meeting. There will therefore be
the usual time for participant discussion.
Talks will take place in Room J11, on the sixth floor
of the Hicks Building.

- 11.00 am: Coffee in I15

- 11.30 am: Andy Baker (Glasgow)

``Artin-Schreier extensions and the Adams spectral sequence for elliptic cohomology.'' - 2.30 pm: Jorge Devoto (Buenos Aires)

``Level 1 equivariant elliptic cohomology'' - 3.30 pm: Tea in I15

- 4.00 pm: Taras Panov (Manchester) ``Combinatorics, topology and homotopy theory of toric spaces''

Given a simplicial polytope K, or a more general combinatorial object such as a fan or a simplicial complex, one may produce several different types of spaces acted on by a torus out of it. The common feature of these toric spaces is that their orbit structure is determined by the combinatorics of K. Examples include toric varieties, (quasi)toric manifolds, coordinate subspace arrangement complements and universal "moment" manifolds and complexes. Both ordinary and equivariant cohomology of these toric spaces usually can be described combinatorially, which opens the way to topological treatment of combinatorial invariants of K. Another interesting phenomenon appearing in the equivariant topology of toric spaces is that the corresponding Borel constructions and spaces themselves admit a regular categorical description as the colimits of diagrams over face category of K in different categories. For instance, the Borel constructions associated to all above listed toric spaces are homotopy equivalent to the colimit of the diagram of classifying spaces of tori. The cohomology of the latter colimit space is the Stanley-Reisner face ring of K appearing in the commutative algebra of simplicial complexes. It turns out that for some nice K (namely, when K is a flag complex) the above colimit of classifying spaces is itself the classifying space for the so-called rotation group corresponding to K, which is a continuous analogue of the right-angle Coxeter group W(K). This implies, that in the case of flag complex colimits of the diagrams of tori and classifying spaces for tori determined by K agree (in the sence that the classifying space for the colimit group is the colimit space). If K is not a flag complex, then two colimits no longer agree, and the obstructions are determined by higher Whitehead and Samelson products. Finally, in the case of general K the inconsistence between the diagram of groups and the diagram of classifying spaces can be remedied by replacing colimits with homotopy colimits.

Anyone who wishes to participate is welcome: we shall operate the
usual arrangements for assistance with travel expenses. We expect
to assemble for tea and coffee in I15, Floor 5,
from 11.00 am until the first talk.
Each lecture will take place in Room J11 of the Hicks Building,
Hounsfield Road, Sheffield.

Tea and Coffee will be served in
the common room I15.

For further information email
John Greenlees
j.greenlees@sheffield.ac.uk,
(or John Hunton
jrh7@mcs.le.ac.uk or
Nige Ray
nige@ma.man.ac.uk) if you are interested, so we can make
approximately the right amount of tea and coffee.

The meeting is partially supported by a Scheme 3 grant from the London Mathematical Society.

To TTT29

To TTT31