Topology Seminar

Mon, 20/05 15:45	Yang Su (Beijing)	Topology Seminar	L3
	Fibering 5-manifolds with fundamental group Z over the circle
	In this talk I will introduce my joint work with Kreck on a classification of certain 5-manifolds with fundamental group Z. This result can be interpreted as a generalization of the classical Browder-Levine's fibering theorem to dimension 5.

Mon, 03/06 15:45	Sarah Whitehouse (Sheffield)	Topology Seminar	L3
	Derived A-infinity algebras from the point of view of operads
	A-infinity algebras arise whenever one has a multiplication which is "associative up to homotopy". There is an important theory of minimal models which involves studying differential graded algebras via A-infinity structures on their homology algebras. However, this only works well over a ground field. Recently Sagave introduced the more general notion of a derived A-infinity algebra in order to extend the theory of minimal models to a general commutative ground ring. Operads provide a very nice way of saying what A-infinity algebras are - they are described by a kind of free resolution of a strictly associative structure. I will explain the analogous result for derived A_infinity algebras - these are obtained in the same manner from a strictly associative structure with an extra differential. This is joint work with Muriel Livernet and Constanze Roitzheim.

Mon, 10/06 15:45	Derek Holt (Southampton)	Topology Seminar	L3
	On Sofic Groups
	The class of sofic groups was introduced by Gromov in 1999. It includes all residually finite and all amenable groups. In fact, no group has been proved not to be sofic, so it remains possible that all groups are sofic. Their defining property is that, roughly speaking, for any finite subset F of the group G, there is a map from G to a finite symmetric group, which is approximates to an injective homomorphism on F. The widespread interest in these group results partly from their connections with other branches of mathematics, including dynamical systems. In the talk, we will concentrate on their definition and algebraic properties.

Forthcoming Seminars