Brandeis Topology Seminar, Spring 2026

Organizers: Carolyn Abbott (carolynabbott@brandeis.edu), Dani Álvarez-Gavela (dgavela@brandeis.edu) Kiyoshi Igusa (igusa@brandeis.edu), Thomas Ng (thomasng@brandeis.edu), Surena Hozoori (hozoori@brandeis.edu)

January 15: Seraphina Lee 

Title: Infinitely many Lefschetz pencils on ruled surfaces

Abstract: Works of Donaldson and Gompf show that a closed, oriented 4-manifold admits a symplectic structure if and only if it admits the structure of a Lefschetz pencil. However, the question of how many Lefschetz pencils (or fibrations) a given symplectic 4-manifold admits remains open. Works of Park--Yun and Baykur construct 4-manifolds admitting arbitrarily large (but finite) numbers of Lefschetz pencils or fibrations of the same genus. In this talk, we will construct infinitely many non-isomorphic Lefschetz pencils of the same genus on ruled surfaces of negative Euler characteristic. In fact, our construction gives the first example of infinitely many non-isomorphic but diffeomorphic Lefschetz pencils and fibrations of the same genus. This is joint work in progress with Carlos A. Serván.

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January 29: Isabella Khan (MIT) 

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February 05: Arya Vadnere (Buffalo) 

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February 26: Joe Boninger (Boston College)

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March 12: Daniel Levitin

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March 26: Shaked Bader (Oxford University) 

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April 28 (Brandeis Thursday): 

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