Cross products, automorphisms, and gradings

Crossed Products and Entropy of Automorphisms

Let A be an exact C–algebra, let G be a locally compact group, and let (A, G, α) be a C–dynamical system. Each automorphism αg induces a spatial automorphism Adλg on the reduced crossed product A×α G. In this paper we examine the question, first raised by E. Størmer, of when the topological entropies of αg and Adλg coincide. This had been answered by N. Brown for the particular case of discrete...

Semicrossed Products Generated by Two Commuting Automorphisms

In this paper, we study the semicrossed product of a finite dimensional C∗-algebra for two types of Z2+-actions, and identify them with matrix algebras of analytic functions in two variables. We look at the connections with semicrossed by Z+actions.

Automorphisms of Products of Measure Spaces

Universal Gradings of Orders

An order is a commutative ring of which the additive group is a finitely generated free abelian group, and a graded order is an order that is provided with a grading by some abelian group. Examples are provided by group rings of finite abelian groups over rings of integers in number fields. We generalize known properties of nilpotents, idempotents, and roots of unity in such group rings to the ...

Gradings in Modular Representations

This paper considers Weyl modules for a simple, simply connected algebraic group over an algebraically closed field k of positive characteristic p. The main result proves that Weyl modules have (cogood) p-filtrations subject to restrictions on p. In case the high weight of the Weyl module is p-regular, the p-filtration is compatible with theG1-radical series of the module. This is a preliminary...