One of the weekly highlights during my times at Queens was the joint seminar with Jamie Mingo on free probability and random matrices. This seminar was of course going on after I left Queen’s, and I also installed different versions of that seminar in Saarbrucken, but at least for me it did not feel the same anymore. So I am happy that we decided now to join forces again and revive our joint seminar in online form. For now it is running on Thursdays at 10 am Eastern time, which is 4 pm German time. You can find the program on the seminar page. If you are interested, write to Jamie to be put on the mailing list.

# Category Archives: online seminar

# Talk by Moritz Weber in the Wales MPPM Zoom Seminar

The next Wales MPPM Zoom Seminar will given by **Moritz Weber (Saarland)** on **Tuesday, 23rd November** at **4.30 pm UK time and UTC**.

The title and abstract are:

**Easy quantum groups and quantum permutations**

Within Woronowicz’s framework of compact quantum groups, there are natural quantum analogs of the symmetric group, the orthogonal group and the unitary group, amongst others. They have in common that their representation theory may be expressed in terms of diagrams. This has been systematically formalized by Banica and Speicher in 2009 within the class of so called “easy” quantum groups.We give an introduction to “easy” quantum groups, their diagrammatic representation theory and we mention some links with Deligne’s interpolation categories. Moreover, we highlight the role of quantum permutations within the theory of quantum automorphism groups of graphs. This also links with nonlocal games in quantum information theory, as we will point out.

Further details, including the programme of upcoming talks, are available on the Wales MPPM Zoom Seminar web page (https://davidemrysevans.wordpress.com/wales-mppm-zoom-seminar/), and some previous talks appear on the Wales MPPM YouTube channel.

# Announcement of two talks on free probability at the Technion … and of some more talks

**update (from Jan 27):** the recordings of the talks of Tobias and mine have been uploaded to youtube, here are the direct links:

I will give a colloquium talk at the Math Department of the Technion, Israel on next Monday, January 25 – online, of course. They have the nice option of a pre-colloquium talk, which provides students with some background for the material appearing in the colloquium talk. Tobias agreed to give such a preparation for my talk. So he will give tomorrow (on Thursday, January 21) an introduction to free probability and its relation with random matrices. Surely a great opportunity for everyone to learn (more) about the subject.

My talk will, of course, have such material in the background, but I tried to prepare it in such a way that even without knowing about free probability one should be able to get the main ideas. So, it might help to know what free semi-circulars are, but it is not necessary (and not assumed) for my talk.

Below are the titles and abstracts of our talks; and here is a link to the Technion page with access information:

Colloquium

**update**: actually, next week seems to be a busy week for talks around free probability; don’t forget that the UC Berkeley Probabilistic Operator Algebra Seminar will be starting again, on Monday, January 25, with a talk of Friedrich Goetze; and then there will also be a talk by Serban Belinschi on “The Christoffel-Darboux kernel in noncommutative probability” at the Probability Seminar at Warsaw University of Technology, on Tuesday, January 26.

**Tobias Mai: What actually is free probability theory?** (Thursday, January 21, 2021)

In my talk, I want to answer this question by giving an introduction to the underlying ideas, basic concepts, and fundamental results of free probability theory. In particular, I will highlight the deep connections of this field with random matrix theory.

**Roland Speicher: Singularity of matrices in non-commuting variables and free probability** (Monday, January 25, 2021)

The Edmonds’ problem asks to decide about the singularity of a given matrix with linear polynomials in commuting variables as entries, or more general to compute the rank of such a matrix over the field of rational functions. This problem has no known deterministic polynomial time algorithm and it relates to fundamental questions in complexity theory.

Recently, there has been much interest in analyzing a non-commutative variant of the Edmonds’ problem, where the entries are linear polynomials in non-commuting variables and the rank is over the field of non-commutative rational functions (aka free skew field). Garg, Gurvits, Oliveira, and Wigderson showed that for this non-commutative Edmonds’ problem there exists a deterministic polynomial time algorithm. This problem has a remarkable number of diverse origins and motivations and I will present in my talk another such manifestation of the problem, arising from the relation with free probability and random matrix theory. In particular, this approach results also in another, quite analytic, algorithm for calculating the non-commutative rank.

This talk is based on joint work with Johannes Hoffmann, Tobias Mai, and Sheng Yin.

# Another online seminar: Wales MPPM Zoom Seminar

At the moment there are many online activities going on …. and here is another one: the Wales Mathematical Physics Zoom Seminar, organized by Edwin Beggs, David Evans, Gwion Evans,Rolf Gohm, Tim Porter.

Why do I mention in particular this one; there are at least two reasons. Today there is a talk by Mikael Rordam around the Connes embedding problem, and next week I will give a talk, on my joint work with Tobias Mai and Sheng Yin of the last years around rational functions of random matrices and operators.

If you are interested in any of this, here is the website of the seminar, where you can find more information.

**Update**: The talks are usually recorded and posted on a youtube channel. There you can find my talk on “Random Matrices and Their Limits”.

# Berkeley’s Probabilistic Operator Algebra Seminar (Hosted by Voiculescu) is Now Online

Due to the current conditions, Voiculescu’s seminar on free probability and operator algebras is now being held online via the platform Zoom. Members of the community worldwide are welcome to join.

Announcements and the Zoom link for each talk will be shared via a mailing list. If you would like to be added to this list, please send an email to: jgarzavargas@berkeley.edu

In this webpage you can find the titles, abstracts and dates for** **past and future talks: https://math.berkeley.edu/~jgarzav/seminar.html

Sincerely,

Jorge Garza Vargas