BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Pranav Chakravarthy (Hebrew University of Jerusalem) DTSTART:20211102T163000Z DTEND:20211102T173000Z DTSTAMP:20260423T022620Z UID:Geolis/59 DESCRIPTION:Title: Homotopy type of equivariant symplectomorphisms of rational ruled surfaces \nby Pranav Chakravarthy (Hebrew University of Jerusalem) as part of G eometria em Lisboa (IST)\n\n\nAbstract\nIn this talk\, we present results on the homotopy type of the group of equivariant symplectomorphisms of $S^ 2 \\times S^2$ and $CP^2$ blown up once\, under the presence of Hamiltonia n group actions of either $S^1$ or finite cyclic groups. For Hamiltonian c ircle actions\, we prove that the centralizers are homotopy equivalent to either a torus or to the homotopy pushout of two tori depending on whether the circle action extends to a single toric action or to exactly two non- equivalent toric actions. We can show that the same holds for the centrali zers of most finite cyclic groups in the Hamiltonian group. Our results re ly on J-holomorphic techniques\, on Delzant's classification of toric acti ons\, on Karshon's classification of Hamiltonian circle actions on 4-manif olds\, and on the Chen-Wilczynski smooth classification of $\\mathbb Z_n$- actions on Hirzebruch surfaces.\n LOCATION:https://researchseminars.org/talk/Geolis/59/ END:VEVENT END:VCALENDAR