Info: The AGDM seminar is a joint seminar of the University of Vienna and TU Wien. In winter semesters, we meet on Tuesdays from 15:00 to 16:30 at the University of Vienna. In summer semesters, we meet on Tuesdays from 15:15 to 16:45 at TU Wien.
Since 2025, we use a mailing-list to advertise the seminar. You can register here.
Place: Universität Wien (Oskar-Morgenstern-Platz 1, Seminar Room 9 on the 2nd floor)
Time:Tuesday, 15:00-16:30
| Date: | Tuesday 07.10.2025 |
| Title: | Equiangular lines via improved eigenvalue multiplicity |
| Speaker: | Matija Bucic (University of Vienna) |
| Abstract: | A family of lines passing through the origin in an inner product space is said to be equiangular if every pair of lines defines the same angle. In 1973, Lemmens and Seidel raised what has since become a central question in the study of equiangular lines in Euclidean spaces. They asked for the maximum number of equiangular lines in $R^r$ with a common angle of $\alpha$. This classical question stems its origins from elliptic geometry, and has since found connections and applications to a large number of different areas. Improving on a number of recent breakthroughs we determine the answer up to lower order terms for essentially the whole range of parameters and determine it precisely when $\alpha=\arccos(1/(2k-1))$ for any positive integer $k$, when the dimension is at least exponential in a polynomial in $k$. The key new ingredient underlying our results is an improved upper bound on the multiplicity of the second-largest eigenvalue of a graph. |
Maintaining a respectful environment is essential to fostering meaningful dialogue and intellectual growth. Participants are expected to refrain from any form of disrespectful or inappropriate behaviour, including offensive comments, harassment, or disruptive conduct. Questions and contributions should be constructive, relevant to the topic, and posed in a professional manner that encourages healthy academic exchange. Harassment of any kind—including verbal, moral or physical—will not be tolerated, and all attendees are urged to uphold these principles to ensure a safe and welcoming atmosphere for everyone.
| 14.10.2025 | Christian Krattenthaler | |
| 21.10.2025 | Sergio Fernandez de Soto Guerrero | MathMagic: A positroidal action over a deck of cards |
| 28.10.2025 | Shane Chern |