April 2015 - Geometria_Pisa - Mailing list — Dipartimento di Matematica, UniPI

seminari mercoledì
by Bruno Martelli 13 Apr '15

13 Apr '15

buondì, segnalo due seminari per mercoledì prossimo, il nostro di geometria è anticipato alle 14.30. a presto, Bruno --- Wednesday, April 15, 2015 Ora Inizio: 14:30 Aula: Sala Seminari (Dip. Matematica) Relatore: Paolo Aceto (Università di Firenze) Titolo: Rational homology cobordisms of plumbed 3-manifolds and arborescent link concordance Abstract: We investigate rational homology cobordisms of 3-manifolds with non-zero first Betti number. This is motivated by the natural generalization of the slice-ribbon conjecture to multicomponent links. In particular we consider the problem of which rational homology S^1x S^2's bound rational homology S^1xD^3's. We give a simple procedure to construct rational homology cobordisms between plumbed 3-manifold. We introduce a family F of plumbed 3-manifolds with b_1=1. By adapting an obstruction based on Donaldson's diagonalization theorem we characterize all manifolds in F that bound rational homology S^1xD^3's. For all these manifolds a rational homology cobordism to S^1xS^2 can be constructed via our procedure. The family F is large enough to include all Seifert fibered spaces over the 2-sphere with vanishing Euler invariant. We also describe applications to arborescent link concordance. ---- Wednesday, April 15, 2015 Ora Inizio: 16:00 Aula: Sala Seminari (Dip. Matematica) Relatore: Alberto Abbondandolo (Univ. di Bochum e Univ. di Pisa) Titolo: How long is the shortest geodesic on a sphere?

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seminario domani
by Bruno Martelli 07 Apr '15

07 Apr '15

buondì, vi annuncio il seminario di geometria di domani, al quale siete tutti invitati. a presto, Bruno ---- Wednesday, April 8, 2015 Ora Inizio: 16:00 Aula: Sala Seminari (Dip. Matematica) SEMINARI DI GEOMETRIA Relatore: Antonio De Capua (University of Oxford) Titolo: Hyperbolic volume of links, via pants graphs and train tracks Abstract: A result of Jeffrey Brock states that, given a hyperbolic 3-manifold which is a mapping torus over a surface S, its volume can be expressed in terms of the distance induced by the monodromy map in the pants graph of S. This is an abstract graph whose vertices are pants decompositions of S, and edges correspond to some sort of 'elementary alterations' of those. Brock's theorem motivates investigation about distances in the pants graph; in particular we generalise a result of Masur, Mosher and Schleimer that train track splitting sequences (which will be defined during the talk) induce quasi-geodesics in the marking graph. This will be the core piece of a volume estimate for complements of closed braids in the solid torus.

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summer school "Cohomology and Large Scale Geometry"
by Roberto Frigerio 01 Apr '15

01 Apr '15

Buongiorno, vi segnalo la scuola estiva di cui nel subject, che si terra' a Regensburg dal 27 al 31 luglio. Qui potete trovarne una descrizione: http://clsg.sfb-higher-invariants.de Saluti, Roberto

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