# Geometria em Lisboa Seminar

### Symplectic embeddings and infinite staircases

McDuff and Schlenk determined when a four-dimensional symplectic ellipsoid can be symplectically embedded into a four-dimensional ball. They found that if the ellipsoid is close to round, the answer is given by an infinite staircase determined by Fibonacci numbers, while if the ellipsoid is sufficiently stretched, all obstructions vanish except for the volume obstruction. Infinite staircases have also been found when embedding ellipsoids into polydisks (Frenkel-Muller, Usher) and into the ellipsoid $E(2,3)$ (Cristofaro-Gardiner-Kleinman). We will describe a general approach to the question of when embedding ellipsoids into a toric target has an infinite staircase, where we provide the first obstruction to the existence of a staircase. We use this obstruction to explore infinite staircases for toric symplectic manifolds, identifying three new infinite staircases, and culminating in the conjecture that these are the only toric examples. We will describe further work-in-progress on ellipsoid embedding functions with more general targets. I will not assume any prior acquaintance with infinite staircases and will motivate the talk with plentiful examples and pictures. This talk is based on a number of collaborations with Dan Cristofaro-Gardiner, Alessia Mandini, and Ana Rita Pires; Maria Bertozzi, Emily Maw, Dusa McDuff, Grace Mwakyoma, Ana Rita Pires, Morgan Weiler; and Nicki Magill.