Academic literature on the topic 'Poincaré's polyhedron theorem'

AbstractPoincaré's Polyhedron Theorem is a widely known valuable tool in constructing manifolds endowed with a prescribed geometric structure. It is one of the few criteria providing discreteness of groups of isometries. This work contains a version of Poincaré's Polyhedron Theorem that is applicable to constructing fibre bundles over surfaces and also suits geometries of non-constant curvature. Most conditions of the theorem, being as local as possible, are easy to verify in practice.

1·1. Groups of the first kind. In [11], Patterson proved a hyperbolic space analogue of Khintchine's theorem on simultaneous Diophantine approximation. In order to state Patterson's theorem, some notation and terminology are needed. Let ‖x‖ denote the usual Euclidean norm of a vector x in k+1, k + 1-dimensional Euclidean space, and let be the unit ball model of k + 1-dimensional hyperbolic space with Poincaré metric ρ. A non-elementary geometrically finite group G acting on Bk + 1 is a discrete subgroup of Möb (Bk+l), the group of orientation preserving Mobius transformations preserving Bk + 1, for which there exists some convex fundamental polyhedron with finitely many faces. Since G is non-elementary, the limit set L(G) of G – the set of limit points in the unit sphere Sk of any orbit of G in Bk+1 – is uncountable. The group G is said to be of the first kind if L(G) = Sk and of the second kind otherwise.

In this paper, we precise the asymptotic behavior of Newton polygons of L-functions associated to character sums, coming from certain n variable Laurent polynomials. In order to do this, we use the free sum on convex polytopes. This operation allows the determination of the limit of generic Newton polygons for the sum Δ = Δ1⊕Δ2 when we know the limit of generic Newton polygons for each factor. To our knowledge, these are the first results concerning the asymptotic behavior of Newton polygons for multivariable polynomials when the generic Newton polygon differs from the combinatorial (Hodge) polygon associated to the polyhedron.

Generalizando para o caso do bidisco hiperbólico as construções em (ANANIN; GROSSI; GUSEVISKII, 2011) e em (GROSSI, 2015), provamos que o fibrado trivial (tangente) sobre superfícies de gênero ≥ 1 (≥ 2) admite geometria modelada no bidisco hiperbólico. (O caso do fibrado trivial sobre o toro é particularmente curioso, pois a curvatura é nula na base e em cada fibra, mas não no fibrado.) Além do seu próprio valor intrínseco, estes exemplos se inserem no contexto da conjectura de Gromov, Lawson e Thurston. Originalmente, a conjectura de Gromov, Lawson e Thurston diz que um fibrado de discos sobre uma superfície conexa fechada orientável de gênero ≥ 2 admite métrica hiperbólica completa de curvatura constante se e só se ΙeΙ ≤ Ι XΙ, onde e é o número de Euler do fibrado e X é a caraterística de Euler da base. Posteriomente, observou-se que esta desigualdade também era válida em todos os fibrados de discos sobre superfícies com estrutura hiperbólica complexa (i.e., uniformizados pela 2-bola holomorfa) conhecidos. Por esta razão, passou-se a acreditar que a conjectura depende apenas de curvatura negativa lato sensu (digamos, à la Alexandrov) e não das especificidades de uma geometria hiperbólica particular. O bidisco hiperbólico é o caso mais simples que nos permite testar tal hipótese, pois está no limite de ser hiperbólico (a curvatura é ≤ 0). Construímos os dois casos extremais: = 0 (fibrado trivial) e ΙeΙ = ΙXΙ (fibrado tangente). Além disso, provamos alguns resultados relacionados à teoria de Teichmüller no contexto de fibrados de discos uniformizados pelo bidisco hiperbólico.
Generalizing the constructions in (ANANIN; GROSSI; GUSEVISKII, 2011) and in (GROSSI, 2015) to the hyperbolic bidisc, we show that the trivial (tangent) bundle over genus ≥ 1 (≥ 2) surfaces admits a geometric structure modelled on the hyperbolic bidisc. (The case of the trivial bundle over the torus is particularly interesting because the curvature vanishes on the base and on every fiber, but is non-null on the bundle.) Aside from their intrinsic value, these examples also play a role in the context of the Gromov, Lawson and Thurston conjecture (GLT conjecture). Originally, the GLT conjecture states that a disc bundle over a connected oriented closed surface of genus ≥ 2 admits a complete hyperbolic metric of constant curvature if and only if ΙeΙ ≤ ΙXΙ, where stands for the Euler number of the bundle and , for the Euler characteristic of the base. Afterwards, it was observed that this inequality also holds for every known example of disc bundles over surfaces equipped with complex hyperbolic structure (i.e., uniformized by the holomoprhic 2-ball). So, one started to believe that the conjecture depends only on negative curvature lato sensu (say, à la Alexandrov) and not on the particularities of an specific hyperbolic geometry. The hyperbolic bidisc is the simplest case allowing us to test such hypothesis since it lies on the frontier of being hyperbolic (curvature is ≥ 0). We construct the two extremal cases: e = 0 (trivial bundle) and ΙeΙ = ΙXΙ (tangent bundle). We also prove a few results related to Teichmüllers theory in the context of disc bundles uniformized by the hyperbolic bidisc.