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# 2011 Kemeny Lecture Series

## Vaughan Jones

## Flatland, a great place to do algebra

### Monday, April 11, 2011

### 7-8:00PM

### Filene Auditorium, Moore Hall

**Abstract: **
Edwin Abbott, an English non-mathematician of
the Victorian era, wrote a book called "Flatland"
about life in a two dimensional world, and its
hero's travels to other dimensions.
I will use this dimensional voyage to relate one
of my own which will go from one dimension to
infinitely many, then settle solidly in two
dimensions. The quantum world in two
dimensions is even more bizarre than in three
dimensions and the algebra we will encounter is
being used in an attempt to build a quantum
computer based on these very peculiarities.

**Note:** This talk will be accessible to undergraduates.

**NB:** A PDF version of this announcement
(suitable for posting) is also available.

## The Onset of Wildness

### Monday, April 11, 2011

### 4-5:00PM

### 008 Kemeny Hall

**Abstract: **
There are many instances in mathematics of some phenomenon, depending on a parameter, which is
well behaved for a while but at a certain value of the parameter, becomes wild. The onset of turbulence
is a well known example but there are examples in algebra such as Gabriel's quiver theory.

Subfactors are objects that, among other things, extend the notion of finite groups, their representations and permutation actions. The "size" of a subfactor is measured by a number called its index and one might expect an onset of wildness phenomenon as the index grows. Indeed since the mid 1980's it has been known that there is an A-D-E Coxeter graph classification of subfactors of index less than or equal to four. But Bisch and Haagerup showed that at index 6 the situation is "wild". This is because free product of Z/2Z and Z/3Z is almost a free group. But in subfactor land there is a subfactor of index approximately 2.6 so it is possible that wildness begins at about 5.2. There is thus a hope of a complete enumeration of subfactors between index 4 and 5.2. This enumeration begins with Haagerup's subfactor of index and other exotic objects whose existence is only known by combinatorial and planar methods.

## Random matrices, von Neumann algebras and (2+1)-dimensional topological quantum ﬁeld theories.

### Tuesday, April 12, 2011

### 4-5:00PM

### 008 Kemeny Hall

**Abstract: **
Voiculescu used the large N limit of random matrices to define a trace on
the algebra of noncommutative polynomials. A few years ago, Guionnet,
Shlyakhetnko and I discovered how to extend the Voiculescu trace to more
general graded algebras coming from planar algebras. These
(non-commutative) graded algebras have a formal resemblance to the
canonical ring of an algebraic variety. Among the constructions arising in
this work was a notion of matrix model where the number of matrices is non
integral. Planar ideas lead to the consideration of potentials in matrix
models which allow enumeration of various planar structures. In more
recent work Curran and Shlyakhtenko have used the ideas to give a
“visible” construction of the quantum double of a subfactor.