3,907 research outputs found
Another look at anomalous J/Psi suppression in Pb+Pb collisions at P/A = 158 GeV/c
A new data presentation is proposed to consider anomalous
suppression in Pb + Pb collisions at GeV/c. If the inclusive
differential cross section with respect to a centrality variable is available,
one can plot the yield of J/Psi events per Pb-Pb collision as a function of an
estimated squared impact parameter. Both quantities are raw experimental data
and have a clear physical meaning. As compared to the usual J/Psi over
Drell-Yan ratio, there is a huge gain in statistical accuracy. This
presentation could be applied advantageously to many processes in the field of
nucleus-nucleus collisions at various energies.Comment: 6 pages, 5 figures, submitted to The European Physical Journal C;
minor revisions for final versio
Distinction of representations via Bruhat-Tits buildings of p-adic groups
Introductory and pedagogical treatmeant of the article : P. Broussous
"Distinction of the Steinberg representation", with an appendix by Fran\c{c}ois
Court\`es, IMRN 2014, no 11, 3140-3157. To appear in Proceedings of Chaire Jean
Morlet, Dipendra Prasad, Volker Heiermann Ed. 2017. Contains modified and
simplified proofs of loc. cit. This article is written in memory of
Fran\c{c}ois Court\`es who passed away in september 2016.Comment: 33 pages, 4 figure
On abstract commensurators of groups
We prove that the abstract commensurator of a nonabelian free group, an
infinite surface group, or more generally of a group that splits appropriately
over a cyclic subgroup, is not finitely generated.
This applies in particular to all torsion-free word-hyperbolic groups with
infinite outer automorphism group and abelianization of rank at least 2.
We also construct a finitely generated, torsion-free group which can be
mapped onto Z and which has a finitely generated commensurator.Comment: 13 pages, no figur
Automorphism groups of polycyclic-by-finite groups and arithmetic groups
We show that the outer automorphism group of a polycyclic-by-finite group is
an arithmetic group. This result follows from a detailed structural analysis of
the automorphism groups of such groups. We use an extended version of the
theory of the algebraic hull functor initiated by Mostow. We thus make
applicable refined methods from the theory of algebraic and arithmetic groups.
We also construct examples of polycyclic-by-finite groups which have an
automorphism group which does not contain an arithmetic group of finite index.
Finally we discuss applications of our results to the groups of homotopy
self-equivalences of K(\Gamma, 1)-spaces and obtain an extension of
arithmeticity results of Sullivan in rational homotopy theory
A Note on the Equality of Algebraic and Geometric D-Brane Charges in WZW Models
The algebraic definition of charges for symmetry-preserving D-branes in
Wess-Zumino-Witten models is shown to coincide with the geometric definition,
for all simple Lie groups. The charge group for such branes is computed from
the ambiguities inherent in the geometric definition.Comment: 12 pages, fixed typos, added references and a couple of remark
Ideals of Quasi-Symmetric Functions and Super-Covariant Polynomials for S_n
The aim of this work is to study the quotient ring R_n of the ring
Q[x_1,...,x_n] over the ideal J_n generated by non-constant homogeneous
quasi-symmetric functions. We prove here that the dimension of R_n is given by
C_n, the n-th Catalan number. This is also the dimension of the space SH_n of
super-covariant polynomials, that is defined as the orthogonal complement of
J_n with respect to a given scalar product. We construct a basis for R_n whose
elements are naturally indexed by Dyck paths. This allows us to understand the
Hilbert series of SH_n in terms of number of Dyck paths with a given number of
factors.Comment: LaTeX, 3 figures, 12 page
Conjugacy theorems for loop reductive group schemes and Lie algebras
The conjugacy of split Cartan subalgebras in the finite dimensional simple
case (Chevalley) and in the symmetrizable Kac-Moody case (Peterson-Kac) are
fundamental results of the theory of Lie algebras. Among the Kac-Moody Lie
algebras the affine algebras stand out. This paper deals with the problem of
conjugacy for a class of algebras --extended affine Lie algebras-- that are in
a precise sense higher nullity analogues of the affine algebras. Unlike the
methods used by Peterson-Kac, our approach is entirely cohomological and
geometric. It is deeply rooted on the theory of reductive group schemes
developed by Demazure and Grothendieck, and on the work of J. Tits on buildingsComment: Publi\'e dans Bulletin of Mathematical Sciences 4 (2014), 281-32
Flûte
La flûte est présente dans tout le Magreb, aussi bien dans les populations arabopbones que herbèrophones. Elle est confectionnée à partir d’un tuyau de roseau (de bambou, de métal, voire de matière plastique) ouvert aux deux extrémités et percé d’un certain nombre de trous. Parfois, elle est gravée de motifs décoratifs peints en rouge (comme par exemple en Kabylie) ou pyrogravés. L’embouchure terminale est simple, non aménagée, sinon bisotée. Le musicien tient sa flûte obliquement, pour facil..
Musiques touarègues
La pratique musicale traditionnelle Dans les populations touarègues pratiquant encore le nomadisme saisonnier, ce sont les femmes qui ont le monopole de la musique instrumentale et, parmi elles, celles des classes sociales les plus élevées dans la hiérarchie qui peuvent jouer de la vièle monocorde imẓad * (ou anẓad) alors que les femmes forgeronnes ou ex-captives se limitent au jeu du tambour sur mortier tendey/tindé*. Quand elles chantent en soliste, les femmes le font toujours accompagnées ..
- …