arXiv subjects

Riccardo Piergallini

Publications and source records attributed to Riccardo Piergallini.

23 records · Page 2Linked to original sources

arXiv2006

A universal invariant of four-dimensional 2-handlebodies and three-manifolds

This paper is the second part of our work on 4-dimensional 2-handlebodies. In the first part (arXiv:math.GT/0407032) it is shown that up to certain set of local moves, connected simple coverings of B^4 branched over ribbon surfaces, bijectively represent connected orientable 4-dimensional 2-handlebodies up to 2-deformations (handle slides and creations/cancellations of handles of index <= 2). We factor this bijective correspondence through a map onto the closed morphisms in a universal braided category freely generated by a Hopf algebra object H. In this way we obtain a complete algebraic description of 4-dimensional 2-handlebodies. This result is then used to obtain an analogous description of the boundaries of such handlebodies, i.e. 3-dimensional manifolds, which resolves for closed manifolds the problem posed by Kerler in "Towards an algebraic characterization of 3-dimensional cobordisms", Contemporary Mathematics 318 (2003). (cf. Problem 8-16 (1) in T. Ohtsuki, "Problems on invariants of knots and 3-manifolds", Geom. Topol. Monogr. 4 (2002).

math.GT↗

arXiv2003

A universal ribbon surface in B^4

We construct an orientable ribbon surface F in B^4, which is universal in the following sense: any compact orientable pl 4-manifold having a handle decomposition with 0-, 1- and 2-handles can be represented as a cover of B^4 branched over F.

math.GT↗

arXiv2002

4-manifolds as covers of the 4-sphere branched over non-singular surfaces

We prove the long-standing Montesinos conjecture that any closed oriented PL 4-manifold M is a simple covering of S^4 branched over a locally flat surface (cf [J M Montesinos, 4-manifolds, 3-fold covering spaces and ribbons, Trans. Amer. Math. Soc. 245 (1978) 453--467]). In fact, we show how to eliminate all the node singularities of the branching set of any simple 4-fold branched covering M \to S^4 arising from the representation theorem given in [R Piergallini, Four-manifolds as 4-fold branched covers of S^4, Topology 34 (1995) 497--508]. Namely, we construct a suitable cobordism between the 5-fold stabilization of such a covering (obtained by adding a fifth trivial sheet) and a new 5-fold covering M --> S^4 whose branching set is locally flat. It is still an open question whether the fifth sheet is really needed or not.

math.GT↗

arXiv2001

Lifting Braids

In this paper we study the homeomorphisms of the disk that are liftable with respect to a simple branched covering. Since any such homeomorphism maps the branch set of the covering onto itself and liftability is invariant up to isotopy fixing the branch set, we are dealing in fact with liftable braids. We prove that the group of liftable braids is finitely generated by liftable powers of half-twists around arcs joining branch points. A set of such generators is explicitly determined for the special case of branched coverings from the disk to the disk. As a preliminary result we also obtain the classification of all the simple branched coverings of the disk.

math.GT↗

arXiv2000

Compact Stein surfaces with boundary as branched covers of $\B^4$

We prove that Stein surfaces with boundary coincide up to orientation preserving diffeomorphisms with simple branched coverings of $\B^4$ whose branch set is a positive braided surface. As a consequence, we have that a smooth oriented 3-manifold is Stein fillable iff it has a positive open-book decomposition.

math.GT↗