Geometry and Topology

Speaker: Alex Suciu (Northeastern University)

"Hyperplane arrangements and Milnor fibrations"

Time: 15:30

Room: MC 107

Much of the fascination with arrangements of complex hyperplanes comes from the rich interplay between the combinatorics of the intersection lattice and the algebraic topology of the complement. A key bridge between the two is provided by the resonance varieties of the cohomology ring and by the characteristic varieties of the fundamental group. This approach helps explain how certain homological invariants associated to the Milnor fibration of the complement can be computed in terms of multinets supported by the underlying matroid.

Noncommutative Geometry

Speaker:

"Noncommutative Geometry Workshop at Western University"

Time: 08:30

Room:

This two-days workshop will consist of research talks by experts on three aspects of the subject:

I) Spectral invariants of noncommutative spaces and the spectral action principle,

II) Applications to the standard model of particle physics,

III) Cyclic cohomology and Hopf algebras.

For more information visit:

http://www-home.math.uwo.ca/~masoud/NCGUWO-2015/index.html

Noncommutative Geometry

Speaker:

"Noncommutative Geometry Workshop at Western University"

Time: 08:30

Room:

This two-days workshop will consist of research talks by experts on three aspects of the subject:

I) Spectral invariants of noncommutative spaces and the spectral action principle,

II) Applications to the standard model of particle physics,

III) Cyclic cohomology and Hopf algebras.

For more information visit:

http://www-home.math.uwo.ca/~masoud/NCGUWO-2015/index.html

Noncommutative Geometry

Speaker: Bruno Iochum (Aix-Marseille University)

"Spectral triples and modular extensions"

Time: 14:30

Room: MC 108

Given a spectral triple $(A,H,D)$ and a $C^*$-dynamical system $(\bA, G, \alpha)$ where $A$ is dense in $\bA$ and $G$ is a locally compact group, we extend the triple to a triplet $(\algA,\caH,\DD)$ on the crossed product $G \ltimes_{\alpha, \red} \bA$ which can be promoted to a modular-type twisted spectral triple within a general procedure exemplified by two cases: the $C^*$-algebra of the affine group and the conformal group acting on a complete Riemannian spin manifold.

Dept Oral Exam

Speaker: Baran Serajelahi (Western)

"Quantization of two types of multisymplectic manifold"

Time: 13:30

Room: MC 107

We will be interested in quantization in a setting where the algebraic structure on $C^{\infty}(M)$ is given by an m-ary bracket $\{.,\dots,.\}:\otimes^m C^{\infty}(M)\rightarrow C^{\infty}(M)$. Quantization in this context is the same as in the symplectic case, where we have a bracket of just two functions except that now we are interested in a correspondence $\{.,\dots,.\}\rightarrow [.,\dots,.]$, between an m-ary bracket and a generalizeation of the commutator. In particular we will be interested in two situations where the m-ary bracket comes from an $(m-1)$-plectic form defined on M (i.e. a closed non-degenerate $m$-form), $\Omega$, for $m\ge 1$. The case $m=1$ is when $\Omega$ is symplectic. Let $(M,\omega)$ be a compact connected integral K\"ahler manifold of complex dimension $n$. In both of the cases that we will be looking into, the $(m-1)$-plectic form $\Omega$ on $(M,\omega)$ is constructed from a K\"ahler form (or forms):

(I) $m=2n$, $\Omega = \frac{\omega^n}{n!}$

(II) $M$ is, moreover, hyperk\"ahler, $m=4$, $$ \Omega = \omega_1\wedge \omega_1 + \omega_2\wedge \omega_2 + \omega_3\wedge \omega_3 $$ where $\omega_1, \omega_2, \omega_3$ are the three K\"ahler forms on $M$ given by the hyperk\"ahler structure.

It is well-known (and easy to prove) that a volume form on an oriented $N$-dimensional manifold is an $(N-1)$-plectic form, and that the $4$-form above is a $3$-plectic form on a hyperk\"ahler manifold.

It is intuitively clear that in these two cases the classical multisymplectic system is essentially built from Hamiltonian system(s) and it should be possible to quantize $(M,\Omega)$ using the (Berezin-Toeplitz) quantization of $(M,\omega)$.

Algebra Seminar

Speaker: Chuluun Bekh-Ochir (National University of Mongolia)

"On some $T$-space problems of A. V. Grishin and V. V. Shchigolev"

Time: 11:00

Room: MC 108

V. V. Shchigolev has proved that over any infinite field $k$ of characteristic $p>2$, in the free associative $k$-algebra on a countable number of generators $\{x_n \mid n \ge 1 \}$, the $T$-space generated by $G=\{ x_n^p \mid n \ge 1 \}$ is finitely based, thus answering a question raised by A. V. Grishin. Shchigolev then conjectured that every infinite subset of $G$ generates a finitely based $T$-space. We prove Shchigolev's conjecture is correct over any field of characteristic $p>2$. We also give an upper bound for the size of a minimal generating set for such a $T$-space.

Dept Oral Exam

Speaker: Mayada Shahada (Western)

"Combinatorial polynomial identity theory"

Time: 13:30

Room: MC 107

Algebras with polynomial identities generalize commutative and finite-dimensional algebras. This talk will consist of two parts. Part I examines certain Burnside-type conditions on the multiplicative and the adjoint semigroups associated with an associative algebra $A$. A semigroup $S$ is called $n$-collapsing if, for every $s_1,\ldots,s_n$ in $S$, there exist functions $f\neq g$ (depending on $s_1,\ldots, s_n$), such that

$$s_{f(1)}\cdots s_{f(n)} = s_{g(1)}\cdots s_{g(n)}.$$

More specifically, $S$ is called $n$-rewritable if $f$ and $g$ can be taken to be permutations. Semple and Shalev extended Zelmanov's solution of the Restricted Burnside Problem by proving that every finitely generated residually finite collapsing group is virtually nilpotent. In Part I of this talk, we will consider when the multiplicative semigroup of an associative algebra is collapsing; in particular, we prove the following conditions are equivalent, for all unital algebras $A$ over an infinite field: the multiplicative semigroup of $A$ is collapsing, $A$ satisfies a multiplicative semigroup identity, and $A$ satisfies an Engel identity. Furthermore, we will see that, if the multiplicative semigroup of $A$ is rewritable, then $A$ must be commutative.

In Part II of this talk, we will consider algebraic analogues to well-known problems of Philip Hall on verbal and marginal subgroups of a group. Consider the canonical descending and ascending central series of ideals of an associative algebra $A$:

$$A=A^{(1)}\supseteq A^{(2)}\supseteq \cdots \supseteq A^{(n)}\supseteq \cdots\supseteq 0\quad\text {and}$$ $$0=F^{(0)}(A)\subseteq F^{(1)}(A)\subseteq\cdots \subseteq F^{(n)}(A) \subseteq \cdots \subseteq A.$$

Jennings proved that $A^{(n+1)}=0$ precisely when $A=F^{(n)}(A)$. First we will prove that, if $A/F^{(n)}(A)$ is finite-dimensional, then so is $A^{(n+1)}$. This result is an analogue of a group-theoretic result of Baer, which was proved first by Schur in the case when $n=1$. We also will see that the converse holds whenever $A$ is finitely generated. While this is not true for arbitrary algebras $A$, we do show that, if $A^{(n+1)}$ is finite-dimensional, then at least the quotient $A/F^{(3n-1)}(A)$ is finite-dimensional. These two partial converses are analogues of group-theoretic results due to Hall, albeit with a different bound in the second result. Our main technique is to first describe the ideals $A^{(n+1)}$ and $F^{(n)}(A)$ as the verbal and marginal subspaces of $A$ corresponding to a certain polynomial $g_n$ and then apply Stewart’s result in the algebraic analogue of Hall’s First Problem. Moreover, we will consider algebraic analogues to the other Hall’s Problems and will support them positively in some cases.

Comprehensive Exam Presentation

Speaker: Armin Jamshidpey (Western)

"Rationality Problem for Algebraic Tori"

Time: 15:00

Room: MC 107

In this session I will talk about rationality of algebraic tori. We will first define the notion of rational algebraic variety and then some relaxed notions of rationality. Algebraic tori are important objects in studying algebraic groups.

The rationality problem for an arbitrary group is difficult. Hence it makes sense to study the problem for algebraic groups which have a simple structure.

In order to talk about rationality of algebraic tori we will take a look at the duality between the category of split algebraic tori and the category of G-lattices. We will end the session with the main results about birational classification of tori in small dimensions.