Globals of Completely Regular Monoids

An element of a semigroup S is called irreducible if it cannot be expressed as a product of two elements in S both distinct from itself. In this paper we show that the class C of all completely regular...     

The catenary degrees of elements in numerical monoids generated by arithmetic sequences

We compute the catenary degree of elements contained in numerical monoids generated by arithmetic sequences. We find that this can be done by describing each element in terms of the cardinality of its length set and of its set of factorizations. As a corollary, we find for such monoids that the catenary degree becomes fixed on large elements. This allows us to define and compute the dissonance number- the largest element with a catenary degree different from the fixed value. We determine the dissonance number in terms of the arithmetic sequence’s starting point and its number of generators.     

On uniform acts over semigroups

The paper is devoted to the investigation of uniform acts over semigroups perceived as an overclass of subdirectly irreducible acts. We establish conditions for a uniform act to be subdirectly irreducible. In particular, we prove that uniform acts with two zeros are subdirectly irreducible. Ultimately we investigate monoids which are uniform as right acts over themselves and we describe regular monoids with this property.     

Algebraic monoids and group embeddings

We study the geometry of algebraic monoids. We prove that the group of invertible elements of an irreducible algebraic monoid is an algebraic group, open in the monoid. Moreover, if this group is reductive, then the monoid is affine. We then give a combinatorial classification of reductive monoids by means of the theory of spherical varieties. Partially supported by a CONICYT's grant and the Universidad de la República (Uruguay)     

On the Lattice of Overcommutative Varieties of Monoids

We study the lattice of varieties of monoids, i.e., algebras with two operations, namely, an associative binary operation and a 0-ary operation that fixes the neutral element. It was unknown so far, whether this lattice satisfies some non-trivial identity. The objective of this paper is to give the negative answer to this question. Namely, we prove that any finite lattice is a homomorphic image of some sublattice of the lattice of overcommutative varieties of monoids (i.e., varieties that contain the variety of all commutative monoids). This implies that the lattice of overcommutative varieties of monoids, and therefore, the lattice of all varieties of monoids does not satisfy any non-trivial identity.     

伴随型Renner幺半群的阶

In this paper, we find the orders of the Renner monoids for J-irreducible monoids K＊p（G）, where G is a simple algebraic group over an algebraically closed field K, and p ： G → GL（V） is the irreducible representation associated with the highest root.     

Left and right negatively orderable semigroups where every element has a left and a right identity

We study two classes of modules for order preserving symplectic and order preserving even special orthogonal rook monoids. The first class of modules are indexed by admissible sets, and the second are the regular representations. For the first class we show that every submodule is cyclic and completely reducible, and for each irreducible component when restricted to a module over a proper submonoid we explore its module properties. For the second we provide explicitly their decompositions into irreducible submodules using admissible sets.     

Computation of the complex characters of the group AUT(GL 7(2))

In this paper we find the irreducible complex characters of the automorphism group of the general linear group of degree 7 over a field with two elements. It is shown that this group has 114 irreducible complex characters.     

Analytic monoids and factorization problems

The main goal of this paper is to initiate study of analytic monoids as a general framework for quantitative theory of factorization. So far the latter subject was developed either in concrete settings, for instance in orders of number fields, or abstractly, in an axiomatic way. Some of the abstract approaches are too general to address delicate problems concerning oscillatory nature of the related counting functions, or are too restrictive in the sense that they suffer from the lack of examples except classical ones i.e. the Hilbert monoids of algebraic integers and their products. The notion of an analytic monoid is enough flexible to allow constructions of many other examples, and also ensures sufficiently rich analytic structure. In particular, we construct examples of such monoids with the associated L-functions being products of classical Dirichlet L-functions and L-functions of twisted irreducible unitary cuspidal automorphic representations of \(GL_d({\mathbb {A}}_{\mathbb {Q}})\) satisfying the Ramanujan conjecture and having real coefficients. Finally, to illustrate how a typical problem from the quantitative theory of factorization can be studied in the framework of analytic monoids, we formulate several results concerning oscillations of the remainder term in the asymptotic formula for the number of irreducible elements with norms less or equal x, as x tends to infinity.     

The Minimal Polynomials of Unipotent Elements in Irreducible Representations of the Special Linear Group

The minimal polynomials of images of unipotent elements in irreducible rational representations of a special linear group over an algebraically closed field of characteristic p > 2 are found. In particular, we show that the degree of such polynomial is equal to the order of an element provided the highest weight of a representation is in some sense large enough with respect to p.     

Special elements of the lattice of monoid varieties

We completely classify all neutral and costandard elements in the lattice \(\mathbb {MON}\) of all monoid varieties. Further, we prove that an arbitrary upper-modular element of \(\mathbb {MON}\) except the variety of all monoids is either a completely regular or a commutative variety. Finally, we verify that all commutative varieties of monoids are codistributive elements of \(\mathbb {MON}\). Thus, the problems of describing codistributive or upper-modular elements of \(\mathbb {MON}\) are completely reduced to the completely regular case.     

On the asymptotic behaviour of the number of distinct factorizations into irreducibles

For an integral domainR and a non-zero non-unitaεR we consider the number of distinct factorizations ofa ⁿ into irreducible elements ofR for largen. Precise results are obtained for Krull domains and certain noetherian domains. In fact, we prove results valid for certain classes of monoids which then apply to the above-mentioned classes of domains.     

Cayley-like representations are for all algebras, not merely groups

Cayley 's Theorem represents an arbitrary group as a set of permutations with the group operation captured by the composition of permutations. A few other examples with related representations are monoids, Boolean algebras and Menger algebras, permutations now being replaced by functions with one or more arguments. Although Cayley-like representations appear to be rare, this article shows that they are not. The idea is to represent the elements of an arbitrary algebra by multivariable functions, and its operations by particular compositions of these functions. Any finite algebra can be so represented,and so can any variety generated by one finite subdirectly irreducible algebra. It will follow that these varieties are Cayley-like: semilattices, distributive lattices, median algebras, elementary Abelian p -groups (for fixed p), and those generated by a primal algebra. If the definition of Cayley-like is stretched to allow the representing functions to have an infinite number of arguments, then all algebras are Cayley-like.     

Fixed points of endomorphisms over special confluent rewriting systems

Cayley graphs of monoids defined through special confluent rewriting systems are known to be hyperbolic metric spaces which admit a compact completion given by irreducible finite and infinite words. In this paper, we prove that the fixed point submonoids for endomorphisms of these monoids which are boundary injective (or have bounded length decrease) are rational, with similar results holding for infinite fixed points. Decidability of these properties is proved, and constructibility is proved for the case of bounded length decrease. These results are applied to free products of cyclic groups, providing a new generalization for the case of infinite fixed points.     

Generations for Arithmetic Groups

We prove that any noncocompact irreducible lattice in a higher rank real semi-simple Lie group contains a subgroup of finite index which is generated by three elements.A sizeable part of this paper forms the thesis of R. Sharma, submitted in April 2004 to the Tata Institute of Fundamental Research, Mumbai for the award of a PhD degree.     

Sets of arithmetical invariants in transfer Krull monoids

Transfer Krull monoids are a recently introduced class of monoids and include the multiplicative monoids of all commutative Krull domains as well as of wide classes of non-commutative Dedekind domains. We show that transfer Krull monoids are fully elastic (i.e., every rational number between 1 and the elasticity of the monoid can be realized as the elasticity of an element). In commutative Krull monoids which have sufficiently many prime divisors in all classes of their class group, the set of catenary degrees and the set of tame degrees are intervals. Without the assumption on the distribution of prime divisors, arbitrary finite sets can be realized as sets of catenary degrees and as sets of tame degrees.     

Fixed points of endomorphisms over special confluent rewriting systems

Cayley graphs of monoids defined through special confluent rewriting systems are known to be hyperbolic metric spaces which admit a compact completion given by irreducible finite and infinite words. In this paper, we prove that the fixed point submonoids for endomorphisms of these monoids which are boundary injective (or have bounded length decrease) are rational, with similar results holding for infinite fixed points. Decidability of these properties is proved, and constructibility is proved for the case of bounded length decrease. These results are applied to free products of cyclic groups, providing a new generalization for the case of infinite fixed points.     

On sofic monoids

We investigate a notion of soficity for monoids. A group is sofic as a group if and only if it is sofic as a monoid. All finite monoids, all commutative monoids, all free monoids, all cancellative one-sided amenable monoids, all multiplicative monoids of matrices over a field, and all monoids obtained by adjoining an identity element to a semigroup are sofic. On the other hand, although the question of the existence of a non-sofic group remains open, we prove that the bicyclic monoid is not sofic. This shows that there exist finitely presented amenable inverse monoids that are non-sofic.     

Schreier split epimorphisms between monoids

We explore some properties of Schreier split epimorphisms between monoids, which correspond to monoid actions. In particular, we prove that the split short five lemma holds for monoids, when it is restricted to Schreier split epimorphisms, and that any Schreier reflexive relation is transitive, partially recovering in monoids a classical property of Mal’tsev varieties.