#### Upcoming talks:

6 V | Tristan Bice (Institute of Mathematics of the Czech Academy of Sciences) Étale Groupoids and their C*-Algebras Show abstract We give a general introduction to C*-algebras with a
particular emphasis on those arising from étale groupoids. These
include C*-algebras arising from topological dynamical systems and
various other combinatorial objects like directed graphs. Indeed,
étale groupoids provide a natural lens through which to examine
various combinatorial/dynamical properties and their C*-algebraic
counterparts (e.g. minimality vs simplicity). Time permitting we will
also outline our recent noncommutative extension of the classic
Gelfand duality which unifies classic work of Dauns and Hofmann on
C*-bundles with the more recent Weyl groupoid construction of Kumjian
and Renault. |

6 V | Michal Doucha (Institute of Mathematics of the Czech Academy of Sciences) Strong topological Rohlin property and symbolic dynamics on
countable groups Show abstract Following Hochman, say that a countable group G has the
strong topological Rohlin property (STRP) if it admits a continuous
action on the Cantor space whose conjugacy class is comeager (in an
appropriate topology). It is a well-known result, originally proved by
Kechris and Rosendal and then re-proved by different methods by Akin,
Glasner and Weiss, that there is a generic homeomorphism on the Cantor
space - or in other words, that the group of integers has the STRP. It
was later proved by Hochman that Z^d, for d>1, does not have the STRP,
and by Kwiatkowska that free groups on finitely many generators do
have the STRP.
We show that a countable group G has the STRP if and only if for any
finite set A with at least two elements, in the space of all closed
subshifts of A^G equipped with the Vietoris topology the isolated
points are dense. The latter can be more conveniently restated in the
language of SFTs, which will be done during the talk. Some
applications will be presented, including a new proof of the STRP for
Z. |

Show rest

13 V | Davide Ravotti (University of Vienna) Large hyperbolic circles Show abstract The projections of large circles in R^2 onto the standard torus T^2 become equidistributed as the radius of the circles goes to infinity. In this talk, we consider the analogous problem in the hyperbolic setting; more precisely, for any compact hyperbolic surface, we provide a precise asymptotic expansion of the equidistribution rate of arbitrary circle arcs of large radius. The method we use is inspired by the works of Ratner on quantitative mixing properties of the geodesic flow and of Burger.
Furthermore, we discuss related distributional limit theorems and we give an explicit bound on the error term in the corresponding hyperbolic lattice counting problem (albeit weaker than the known estimates, which have been proved by Selberg and others using number theoretical methods).
This is a joint work with E. Corso. |

The seminar takes place on Fridays

at 10.15-11.45 AM (Kraków time) - currently CEST (UTC+2) in the room 1016

of the Jagiellonian University

Department of Mathematics

and Computer Science

(ul. Łojasiewicza 6, Cracow).