Geometria_Pisa October 2024

geometria_pisa@lists.dm.unipi.it

1 participants
2 discussions

Seminario di Geometria del 22 Ottobre 24 - Miguel Orbegozo Rodriguez
by Carlo Collari 14 Oct '24

14 Oct '24

Buongiorno, segnalo a tutti gli interessati che il prossimo seminario di geometria sarà tenuto da Miguel Orbegozo Rodriguez e si terrà Martedì 22 Ottobre alle ore 14:30 presso l'Aula Riunioni del Dipartimento di Matematica. Inoltre ne aprofitto per ricordare che il seminario di geometria generalmente si terrà il Martedì alle 14:30 invece che il Giovedì alle 11:00. Allego titolo e abstract: Titolo: Murasugi sums and primeness of links Abstact: In this talk I will present some results on how primeness of fibered links behaves under an operation called the Murasugi sum, which generalises the connected sum. As an application, this allows us to resolve a 30 year old conjecture of Cromwell in the case of braid closures. Cromwell showed that, if a link diagram represented as a positive braid features no circles that decompose it as a connected sum (in other words, it is not "obviously" composite), then the link is indeed prime. In his words, "positive braids are visually prime". He further conjectured that the same would hold for link diagrams that yield minimal genus Seifert surfaces when Seifert's algorithm is applied. If the diagram is required to be a braid closure, then Cromwell's condition is equivalent to the braid being homogeneous. Thus, we show that homogeneous braids are visually prime. This is joint work with Peter Feller and Lukas Lewark. <https://www.dm.unipi.it/en/seminar/?id=66fbeae742845121abe42be8> A presto, Carlo

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Seminario di Geometria del 10 Ottobre 24 - Yan Mary He
by Carlo Collari 08 Oct '24

08 Oct '24

Buongiorno, segnalo a tutti gli interessati che il seminario di Yan Mary He si terrà Giovedì 10 Ottobre alle ore 11:00 presso l'Aula Riunioni del Dipartimento di Matematica. Allego titolo e abstract: Titolo: Relative train tracks and endperiodic graph maps Abstact: If G is a connected finite graph (i.e., G has finitely many vertices and edges), a graph map (i.e., a homotopy equivalence) f: G \to G can be viewed as a topological representative of an outer automorphism of the finitely generated free group \pi_1G. The outer automorphism group Out(F_n) of a free group F_n on n generators has been proven to share many similar properties of the mapping class group of a compact surface. If G is an infinite graph (i.e.,G has infinitely many vertices and edges), the structure of a (proper) graph map f: G \to G is more complicated and less understood. Inspired by the recent work of Cantwell-Conlon-Fenley on homeomorphisms of infinite type surfaces, we introduce and study endperiodic graph maps f: G \to G where G has finitely many ends. We prove that any such a map is homotopic to an endperiodic relative train track map, which is a normal form for an endperiodic graph map. Moreover, we show that the Perron-Frobenius eigenvalue of the transition matrix is a canonical quantity associated to the map. This is joint work with Chenxi Wu. link: https://www.dm.unipi.it/en/seminar/?id=66fbeae742845121abe42be8<https://www.dm.unipi.it/en/seminar/?id=66fbeae742845121abe42be8> <https://www.dm.unipi.it/en/seminar/?id=66fbeae742845121abe42be8> A presto, Carlo

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Geometria_Pisa October 2024