arXiv subjects

Patrik Lundström

Publications and source records attributed to Patrik Lundström.

26 records · Page 2Linked to original sources

arXiv2012

Simple Skew Category Algebras Associated with Minimal Partially Defined Dynamical Systems

In this article, we continue our study of category dynamical systems, that is functors $s$ from a category $G$ to $\Top^{\op}$, and their corresponding skew category algebras. Suppose that the spaces $s(e)$, for $e \in \ob(G)$, are compact Hausdorff. We show that if (i) the skew category algebra is simple, then (ii) $G$ is inverse connected, (iii) $s$ is minimal and (iv) $s$ is faithful. We also show that if $G$ is a locally abelian groupoid, then (i) is equivalent to (ii), (iii) and (iv). Thereby, we generalize results by Öinert for skew group algebras to a large class of skew category algebras.

math.RA↗

arXiv2011

Skew Category Algebras Associated with Partially Defined Dynamical Systems

We introduce partially defined dynamical systems defined on a topological space. To each such system we associate a functor $s$ from a category $G$ to $\Top^{\op}$ and show that it defines what we call a skew category algebra $A \rtimes^σ G$. We study the connection between topological freeness of $s$ and, on the one hand, ideal properties of $A \rtimes^σ G$ and, on the other hand, maximal commutativity of $A$ in $A \rtimes^σ G$. In particular, we show that if $G$ is a groupoid and for each $e \in \ob(G)$ the group of all morphisms $e \rightarrow e$ is countable and the topological space $s(e)$ is Tychonoff and Baire, then the following assertions are equivalent: (i) $s$ is topologically free; (ii) $A$ has the ideal intersection property, that is if $I$ is a nonzero ideal of $A \rtimes^σ G$, then $I \cap A \neq \{0\}$; (iii) the ring $A$ is a maximal abelian complex subalgebra of $A \rtimes^σ G$. Thereby, we generalize a result by Svensson, Silvestrov and de Jeu from the additive group of integers to a large class of groupoids.

math.RA↗

arXiv2011

Elementary Magma Gradings on Rings

Suppose that $G$ and $H$ are magmas and that $R$ is a strongly $G$-graded ring. We show that there is a bijection between the set of elementary (nonzero) $H$-gradings of $R$ and the set of (zero) magma homomorphisms from $G$ to $H$. Thereby we generalize a result by Dăscălescu, Năstăsescu and Rios Montes from group gradings of matrix rings to strongly magma graded rings. We also show that there is an isomorphism between the preordered set of elementary (nonzero) $H$-filters on $R$ and the preordered set of (zero) submagmas of $G \times H$. These results are applied to category graded rings and, in particular, to the case when $G$ and $H$ are groupoids. In the latter case, we use this bijection to determine the cardinality of the set of elementary $H$-gradings on $R$.

math.RA↗

arXiv2010

Miyashita Action in Strongly Groupoid Graded Rings

We determine the commutant of homogeneous subrings in strongly groupoid graded rings in terms of an action on the ring induced by the grading. Thereby we generalize a classical result of Miyashita from the group graded case to the groupoid graded situation. In the end of the article we exemplify this result. To this end, we show, by an explicit construction, that given a finite groupoid $G$, equipped with a nonidentity morphism $t : d(t) \to c(t)$, there is a strongly $G$-graded ring $R$ with the properties that each $R_s$, for $s \in G$, is nonzero and $R_t$ is a nonfree left $R_{c(t)}$-module.

math.RA↗

arXiv2010

The Ideal Intersection Property for Groupoid Graded Rings

We show that if a groupoid graded ring has a certain nonzero ideal property, then the commutant of the center of the principal component of the ring has the ideal intersection property, that is it intersects nontrivially every nonzero ideal of the ring. Furthermore, we show that for skew groupoid algebras with commutative principal component, the principal component is maximal commutative if and only if it has the ideal intersection property.

math.RA↗

arXiv2009

Noncrossed Product Matrix Subrings and Ideals of Graded Rings

We show that if a groupoid graded ring has a certain nonzero ideal property and the principal component of the ring is commutative, then the intersection of a nonzero twosided ideal of the ring with the commutant of the principal component of the ring is nonzero. Furthermore, we show that for a skew groupoid ring with commutative principal component, the principal component is maximal commutative if and only if it is intersected nontrivially by each nonzero ideal of the skew groupoid ring. We also determine the center of strongly groupoid graded rings in terms of an action on the ring induced by the grading. In the end of the article, we show that, given a finite groupoid $G$, which has a nonidentity morphism, there is a ring, strongly graded by $G$, which is not a crossed product over $G$.

math.RA↗

arXiv2009

Hilbert 90 for Algebras with Conjugation

We show a version of Hilbert 90 that is valid for a large class of algebras many of which are not commutative, distributive or associative. This class contains the nth iteration of the Conway-Smith doubling procedure. We use our version of Hilbert 90 to parametrize all solutions in ordered fields to the norm one equation for such algebras.

math.RA↗

arXiv2008

Commutativity and Ideals in Category Crossed Products

In order to simultaneously generalize matrix rings and group graded crossed products, we introduce category crossed products. For such algebras we describe the center and the commutant of the coefficient ring. We also investigate the connection between on the one hand maximal commutativity of the coefficient ring and on the other hand nonemptyness of intersections of the coefficient ring by nonzero twosided ideals.

math.RA↗