Search results for "GEOMETRIA"

Nilpotent Groups and Bi-Lipschitz Embeddings Into L1

2022

We prove that if a simply connected nilpotent Lie group quasi-isometrically embeds into an L1 space, then it is abelian. We reach this conclusion by proving that every Carnot group that bi-Lipschitz embeds into L1 is abelian. Our proof follows the work of Cheeger and Kleiner, by considering the pull-back distance of a Lipschitz map into L1 and representing it using a cut measure. We show that such cut measures, and the induced distances, can be blown up and the blown-up cut measure is supported on “generic” tangents of the original sets. By repeating such a blow-up procedure, one obtains a cut measure supported on half-spaces. This differentiation result then is used to prove that bi-Lipsch…

Topics in the geometry of non-Riemannian lie groups

2017

The case of equality in the dichotomy of Mohammadi-Oh

2017

If $n \geq 3$ and $\Gamma$ is a convex-cocompact Zariski-dense discrete subgroup of $\mathbf{SO}^o(1,n+1)$ such that $\delta_\Gamma=n-m$ where $m$ is an integer, $1 \leq m \leq n-1$, we show that for any $m$-dimensional subgroup $U$ in the horospheric group $N$, the Burger-Roblin measure associated to $\Gamma$ on the quotient of the frame bundle is $U$-recurrent.

A Survey of Some Arithmetic Applications of Ergodic Theory in Negative Curvature

2017

This paper is a survey of some arithmetic applications of techniques in the geometry and ergodic theory of negatively curved Riemannian manifolds, focusing on the joint works of the authors. We describe Diophantine approximation results of real numbers by quadratic irrational ones, and we discuss various results on the equidistribution in \(\mathbb{R}\), \(\mathbb{C}\) and in the Heisenberg groups of arithmetically defined points. We explain how these results are consequences of equidistribution and counting properties of common perpendiculars between locally convex subsets in negatively curved orbifolds, proven using dynamical and ergodic properties of their geodesic flows. This exposition…

Eukleideen geometriaa

2018

Eukleides Aleksandrialainen oli kreikkalainen matemaatikko, joka loi noin 300 eaa. euklidisen geometrian. Hän julkaisi euklidisen geometrian perustana olevat aksioomat ja perusolettamukset teoksessaan Alkeet. Eukleideen teos on säilynyt koulujen geometrian opetuksen pohjana jopa 1800–luvulle asti. Päälähteenä tutkielmassa on käytetty Eukleideen teoksen Pekka Aschanin suomennosta ja sen nykysuomennosta kommentteineen, jonka on toimittanut Lauri Kahanpää teoksessa Alkeet, Kuusi ensimmäistä kirjaa eli tasogeometria. Tutkielma tarkastelee Eukleideen muodostamaa teoriaa. Tavoitteena on ratkaista neljä vaativaa ympyrän ja kolmion välistä ongelmaa Eukleideen teorian pohjalta. Eukleideen aksioomajä…

Euklidisen ja hyperbolisen geometrian malleja

2008

The Euler characteristics of $mathcal H_g,n$

2007

In this short note, we compute the orbifold and the ordinary Euler characteristic of Hg,n, the moduli space of pointed hyper- elliptic curves. As a by-product, we obtain an identity involving hypergeometric functions.

A formula for the Euler characteristic of $\overline{{\cal M}}_{2,n}$

2001

In this paper we compute the generating function for the Euler characteristic of the Deligne-Mumford compactification of the moduli space of smooth n-pointed genus 2 curves. The proof relies on quite elementary methods, such as the enumeration of the graphs involved in a suitable stratification of \(\overline{{\cal M}}_{2,n}\).

Euler Characteristics of Moduli Spaces of Curves

2005

Let ${mathcal M}_g^n$ be the moduli space of n-pointed Riemann surfaces of genus g. Denote by ${\bar {\mathcal M}}_g^n$ the Deligne-Mumford compactification of ${mathcal M}_g^n$. In the present paper, we calculate the orbifold and the ordinary Euler characteristic of ${\bar {\mathcal M}}_g^n$ for any g and n such that n>2-2g.

MR 2831984 Reviewed Masuda T. Families of finite coverings of the Riemann sphere. Osaka J. Math. 48 (2011), no. 2, 515--540. (Reviewer Francesca Vetr…

2012

Let $G$ be a finite group and let $H$ be a subgroup of $G$ which does not contain normal subgroups of $G$ except $\{ id \}$. The group $G$ acts on the set of the left coset of $G / H$ as follows: \begin{center} $(g, H a) \rightarrow H a g^{- 1}$. \end{center} The author observes that the action defined above is effective and this gives a permutation representation of $G$, $R: G \rightarrow S_{d}$, where $d =[G : H]$. The condition on $H$ ensures that $R$ is injective. Thus, $G$ can be seen as a transitive subgroup of $S_{d}$. Let $X$ and $ Y$ be connected complex varieties. A finite covering $f: X \rightarrow Y$, which branches at most at $B$, is said a $(G, H)-$coverings if there is a surj…