Schur Indices and Modular Representations.
In this expository paper, we present several open problerns in number theory that have arisen while doing research in group theory. These problems are on arithmetical functions or partitions. Solving some of these problems would allow to solve some open problem in group theory.[Proceedings of the Primeras Jornadas de Teoría de Números (Vilanova i la Geltrú (Barcelona), 30 June - 2 July 2005)].
This paper gives necessary and sufficient conditions for subgroups with trivial core to be of odd depth. We show that a subgroup with trivial core is an odd depth subgroup if and only if certain induced modules from it are faithful. Algebraically this gives a combinatorial condition that has to be satisfied by the subgroups with trivial core in order to be subgroups of a given odd depth. The condition can be expressed as a certain matrix with -entries to have maximal rank. The entries of the matrix...
We introduce the notion of a supersymmetry class of tensors which is the ordinary symmetry class of tensors with a natural ℤ₂-gradation. We give the dimensions of even and odd parts of this gradation as well as their natural bases. Also we give a necessary and sufficient condition for the odd or even part of a supersymmetry class to be zero.
Nous définissons une représentation des groupes d’Artin de type par monodromie de systèmes KZ généralisés, dont nous montrons qu’elle est isomorphe à la représentation de Krammer généralisée définie originellement par A.M.Cohen et D.Wales, et indépendamment par F.Digne. Cela implique que tous les groupes d’Artin purs de type sphérique sont résiduellement nilpotents-sans-torsion, donc (bi-)ordonnables. En utilisant cette construction nous montrons que ces représentations irréductibles sont Zariski-denses...
A finite group whose irreducible characters are rational valued is called a rational or a Q-group. In this paper we obtain various results concerning the structure of a Sylow 2-subgroup of a solvable Q-group.