# Events for 10/15/2021 from all calendars

## Mathematical Physics and Harmonic Analysis Seminar

**Time: ** 1:50PM - 2:40PM

**Location: ** BLO306&Zoom

**Speaker: **Amir Sagiv, Columbia University

**Title: ***Floquet Hamiltonians - effective gaps and resonant decay*

**Abstract: **Floquet topological insulators are an emerging category of materials whose properties are transformed by time-periodic forcing. Can their properties be understood from their first-principles continuum models, i.e., from a driven Schrodinger equation?
First, we study the transformation of graphene from a conductor into an insulator under a time-periodic magnetic potential. We show that the dynamics of certain wave-packets are governed by a Dirac equation, which has a spectral gap property. This gap is then carried back to the original Schrodinger equation in the form of an “effective gap” - a new and physically-relevant relaxation of a spectral gap.
Next, we consider periodic media with a localized defect, and ask whether edge/defect modes remain stable under forcing. In a model of planar waveguides, we see how such modes decay and disappear due to resonant coupling with the radiation modes.

## Algebra and Combinatorics Seminar

**Time: ** 3:00PM - 4:00PM

**Location: ** BLOC 302

**Speaker: **Eric Rowell, TAMU

**Title: ***Zesting Braided Fusion Categories*

**Abstract: **I will describe a construction of new fusion categories from a given G-graded braided fusion category known as zesting. Zesting fits into the general theory of G-graded extensions and so are subject to the cohomological yin and yang of obstructions and parameterization torsors. On the other hand, zesting has several computational advantages. To name a few: the fusion rules are immediately available, we may easily explore braiding and pivotal structures, and when the resulting category is modular the data can be expressed succinctly in terms of the original data. These ideas will be illustrated with examples.