Contact

**Secretary**

Evelyne Bachmann

**Address**

Mathematisches Institut

Universität Heidelberg

Im Neuenheimer Feld 205

69120 Heidelberg, Germany

Opening of the Research Station

July 21 at IWH

Welcome to the Research Station *Geometry + Dynamics*!
We will inaugurate the research station with a small celebration on July 21st at the International Academic Forum Heidelberg (IWH).
For the scientific part three of our current international guests will give us short insights in their research, Michael Gekhtman (Notre Dame University), Sergei Tabachnikov (Penn State University) and Richard Schwartz (Brown University).
Afterwards a reception will be held in the wonderful garden of the IWH.

Talks

**Michael Gekhtman: Discrete Dynamics from Cluster Algebras **

Cluster algebras were introduced by Fomin and Zelevinsky 20 years ago and have since found exciting applications in many areas including algebraic geometry, representation theory, integrable systems and theoretical physics. I will use examples to illustrate how combinatorial ingredients in the definition of a cluster algebra can be interpreted using Poisson geometry and Hamiltonian formalism and then sketch several applications of the theory, including Somos-5 recurrence, pentagram map and its generalizations and dilogarithm identities.

**Sergei Tabachnikov: Cusps of caustics by reflection**

The boundary of a planar oval is an ideal mirror, and one has a point source of light inside the oval. Consider the rays of light that have undergone N reflection in the mirror, where N=1,2,... The envelope of this system of rays is the Nth caustic by reflection. I shall explain that, for every N, this caustic has at least four cusps. Similar problems for convex surfaces were considered before: Caratheodory proved that the locus of points conjugated to a given point has at least four cusps, and Jacobi stated, in his "Lectures on dynamics", that this number is exactly four in the case of the ellipsoid (this is known as the "Last Geometric Statement of Jacobi"). Our problem is a billiard version of these problems of differential geometry of surfaces, and it belongs to an endless collections of results stemmed from and motivated by the classical 4-vertex theorem of Mukhopadhyaya.

**Richard Schwartz: The farthest point map on platonic solids**

Imagine two points, Alice and Bob, sitting on the surface of a regular dodecahedron (equipped with its path metric). Alice and Bob dislike each other, so Alice runs away to the point farthest away from Bob. Then Bob runs away to the point farthest away from the new location of Alice. And so on. Where do Alice and Bob go? In this talk I will explain the dynamics of this process, which is called "the farthest point map". A complete understanding of what happens involves a computer-assisted exploration of something called the cut locus of the regular dodecahedron.

Schedule

Schedule | ||

14:00 - 14:30 | Coffee Break | |

14:30 - 14:45 | Welcome | |

14:45 - 15:15 | Michael Gekhtman | |

15:15 - 15:45 | Coffe Break | |

15:45 - 16:15 | Sergei Tabachnikov | |

16:30 - 17:00 | Richard Schwartz | |

17:00 | Reception in the garden | |

Research Station Geometry & Dynamics - Contact: geodyn@mathi.uni-heidelberg.de. |