Simple Submodules Research Articles

The Computational Complexity of Subclasses of Semiperfect Rings

This paper studies the computational complexity of subclasses of semiperfect rings from the perspective of computability theory. A ring is semiperfect if the identity can be expressed as a sum of mutually orthogonal local idempotents. Semisimple rings and local rings are typical subclasses of semiperfect rings that play important roles in noncommutative algebra. First, we define a ring to be semisimple if the left regular module can be decomposed as a finite direct sum of simple submodules and prove that the index set of computable semisimple rings is Σ20-hard within the index set of computable rings. Second, we define local rings by using equivalent properties of non-left invertible elements of rings and show that the index set of computable local rings is Π20-hard within the index set of computable rings. Finally, based on the Π20 definition of local rings, computable semiperfect rings can be described by Σ30 formulas. As a corollary, we find that the index set of computable semiperfect rings can be both Σ20-hard and Π20-hard within the index set of computable rings.

Simple-separable modules

A module $M$ over a ring is called simple-separable if every simple submodule of $M$ is contained in a finitely generated direct summand of $M$. While a direct sum of any family of simple-separable modules is shown to be always simple-separable, we prove that a direct summand of a simple-separable module does not inherit the property, in general. It is also shown that an injective module $M$ over a right noetherian ring is simple-separable if and only if $M=M_1 \oplus M_2$ such that $M_1$ is separable and $M_2$ has zero socle. The structure of simple-separable abelian groups is completely described.

A remark on 0-cycles as modules over algebras of finite correspondences

Given a smooth projective variety $X$ over a field, consider the $\mathbb Q$-vector space $Z_0(X)$ of 0-cycles (that is, formal finite $\mathbb Q$-linear combinations of closed points of $X$) as a module over the algebra of finite correspondences. Then the rationally trivial 0-cycles on $X$ form an absolutely simple and essential submodule of $Z_0(X)$. Bibliography: 15 titles.

On simple submodules and C-rings

In this paper; we will study the relationship between simple submodules of M and the C-ring. A ring R is called C-ring if every torsion module M over R has simple submodules. We investigated that if M is a torsion module over a semisimple ring; so, R is C-ring. Also, we study C-ring when R is Noetherian and T(M) = M such that any direct sum of modules with (SIP) has (SSP) implies that R is C- ring. We proved that if M is a torsion module and M = W + W′, this means R is C-ring where W and W′ are direct sum of M.

Taylor Spectrum for Modules over Lie Algebras

In this paper we generalize the notion of the Taylor spectrum to modules over an arbitrary Lie algebra and study it for finite-dimensional modules. We show that the spectrum can be described as the set of simple submodules in the case of nilpotent and semisimple Lie algebras. We also show that this result does not hold for solvable Lie algebras and obtain a precise description of the spectrum in the case of Borel subalgebras of semisimple Lie algebras.

Modules that are finite sums of simple submodules

Modules that are finite sums of simple submodules

The computational complexity of module socles

This paper studies the computational complexity of socles of modules from the viewpoint of computability theory. The socle Soc(M) of a module M over a commutative ring R is the sum of all simple submodules of M. Soc(M) plays a vital role in module theory and it is known as the largest semisimple submodule of M. Socles of Z-modules (i.e., abelian groups) are Σ10 and there is a computable abelian group G such that Soc(G) is Σ10-complete. Socles of R-modules are Σ30. We show that there is a computable module M over a computable commutative ring R such that Soc(M) is Σ30-complete.

Crystal of affine type [formula omitted] and Hecke algebras at a primitive 2ℓth root of unity

Let ℓ∈N with ℓ>1. In this paper we give a new realization of the crystal of affine type Aˆℓ−1 using the modular representation theory of the affine Hecke algebras Hn of type A and their level two cyclotomic quotients with Hecke parameter being a primitive 2ℓth root of unity. We construct “hat” versions of i-induction and i-restriction functors on the category RepI(Hn) of finite dimensional integral modules over Hn, which induce Kashiwara operators on a suitable subgroup of the Grothendieck groups of RepI(Hn). For any simple module M∈RepI(Hn), we prove that the simple submodules of resHn−2HnM which belong to Bˆ(∞) (Definition 5.1) occur with multiplicity two. The main results generalize the earlier work of Grojnowski and Vazirani on the relations between the crystal of slˆℓ and the affine Hecke algebras of type A at a primitive ℓth root of unity.

Some results on the quotient of co-m modules

Let $R$ be a commutative ring with identity and let $M$ be a unitary $R$-module. In this paper, among various results, we prove that if $M$ is a cancellation $R$-module and $L$ is a nonzero simple submodule of $M$, then $L$ is a copure submodule of $M$. Moreover, in this case, if $M$ is co-m, then $M/L$ is also a co-m $R$-module. We investigate various conditions under which the quotient module $M/N$ of a co-m $M$ is also a co-m. We prove that if $M$ is a cancellation Noetherian co-m module, then for every second submodule $N$ of $M$ the quotient module $M/N$ is a co-m $R$-module. We obtain some results concerning socle and radical of co-m modules.

A filtration on the ring of Laurent polynomials and representations of the general linear Lie algebra

We first present a filtration on the ring Ln of Laurent polynomials such that the direct sum decomposition of its associated graded ring grLn agrees with the direct sum decomposition of grLn, as a module over the complex general linear Lie algebra gl(n), into its simple submodules. Next, generalizing the simple modules occurring in the associated graded ring grLn, we give some explicit constructions of weight multiplicity-free irreducible representations of gl(n).

On subprojectivity domains of g-semiartinian modules

The aim of this paper is to reveal the relationship between the proper class generated projectively by g-semiartinian modules and the subprojectivity domains of g-semiartinian modules. A module [Formula: see text] is called g-semiartinian if every nonzero homomorphic image of [Formula: see text] has a singular simple submodule. It is proven that every g-semiartinian right [Formula: see text]-module has an epic projective envelope if and only if [Formula: see text] is a right PS ring if and only if every subprojectivity domain of any g-semiartinian right [Formula: see text]-module is closed under submodules. A g-semiartinian module whose domain of subprojectivity as small as possible is called gsap-indigent. We investigated the structure of rings whose (simple, coatomic) g-semiartinian right modules are gsap-indigent or projective. Furthermore, over right PS rings, necessary and sufficient condition to be gsap-indigent module was determined.

Actions between sets. Arbitrarily graded linear modules

We consider maps between arbitrary non-empty sets and and show that if f fixes some element in , then this map induces an adequate decomposition of as the disjoint-pointed union of well-described f-invariant subsets (submodules). If is furthermore a division set-module, it is shown that the above decomposition is by means of the family of its pointed simple submodules. The obtained results are applied to the structure theory of arbitrarily graded linear modules by stating a second Wedderburn type theorem for the class of linear modules with an arbitrary weak-division grading.

A Note on the Dimension of the Largest Simple Hecke Submodule

Abstract For $k\geq 2$ even, let $d_{k,N}$ denote the dimension of the largest simple Hecke submodule of $S_{k}(\Gamma _0(N); {\mathbb{Q}})^{\textrm{new}}$. We show, using a simple analytic method, that $d_{k,N} \gg _k \log \log N / \log (2p)$ with $p$, the smallest prime co-prime to $N$. Previously, bounds of this quality were only known for $N$ in certain subsets of the primes. We also establish similar (and sometimes stronger) results concerning $S_{k}(\Gamma _0(N), \chi )$, with $k \geq 2$ an integer and $\chi $ an arbitrary nebentypus.

Detecting Large Simple Rational Hecke Modules for Γ0(N) via Congruences

Abstract We describe a novel method for bounding the dimension $d$ of the largest simple Hecke submodule of $S_{2}(\Gamma _{0}(N);\mathbb{Q})$ from below. Such bounds are of interest because of their relevance to the structure of $J_{0}(N)$, for instance. In contrast with previous results of this kind, our bound does not rely on the equidistribution of Hecke eigenvalues. Instead, it is obtained via a Hecke-compatible congruence between the target space and a space of modular forms whose Hecke eigenvalues are easily controlled. We prove conditional bounds, the strongest of which is $d\gg _{\epsilon } N^{1/2-\epsilon }$ over a large set of primes $N$, contingent on Soundararajan’s heuristics for the class number problem and Artin’s conjecture on primitive roots. For prime levels $N\equiv 7\mod 8,$ our method yields an unconditional bound of $d\geq \log _{2}\log _{2}(\frac{N}{8})$, which is larger than the known bound of $d\gg \sqrt{\log \log N}$ due to Murty–Sinha and Royer. A stronger unconditional bound of $d\gg \log N$ can be obtained in more specialized (but infinitely many) cases. We also propose a number of Maeda-style conjectures based on our data, and we outline a possible congruence-based approach toward the conjectural Hecke simplicity of $S_{k}(\textrm{SL}_{2}(\mathbb{Z});\mathbb{Q})$.

Simple continuous modules

A module $M$ is called a simple continuous module if it satisfies the conditions $(min-C_{1})$ and $(min-C_{2})$. A module $M$ is called singular simple-direct-injective if for any singular simple submodules $A$, $B$ of $M$ with $A\cong B\mid M$, then $A\mid M$. Various basic properties of these modules are proved, and some well-studied rings are characterized using simple continuous modules and singular simple-direct-injective modules. For instance, it is shown that a ring $R$ is a right $V$-ring if and only if every right $R$-module is a simple continuous modules, and that a regular ring $R$ is a right $GV$-ring if and only if every cyclic right $R$-module is a singular simple-direct-injective module.

On representation of polynomial ring on a vector space via a linear transformation

A representation of a ring R is a ring homomorphism from R to the ring of all linear transformations from V to V (EndF (V)). From the field F, we can form a polynomial ring F[X]. A representation of F[X] is a ring homomorphism φ: F[X] → EndF (V ) via linear transformation T : V → V with φ(f(X)) = f(T) for all f(X) ∈ F[X]. For general ring representation ρ: R → EndF (V), we have notions of admissibility submodule, and completely reducible and simple admissible submodule. In this paper, we will show that admissible submodules of V are invariant under T, and a representation of F[X] is completely reducible.

Uniform almost relative injective modules

The concept of a module M being almost N-injective where N is some module, was introduced by Baba (1989). For a given module M, the class of modules N, for which M is almost N-injective, is not closed under direct sums. Baba gave a necessary and sufficient condition under which a uniform finite length module U is almost V-injective, where V is a finite direct sum of uniform, finite length modules, in terms of extending properties of simple submodules of V. Let U be a uniform module and V be a finite direct sum of indecomposable modules. Recently, Singh (2016), has determined some conditions under which U is almost V injective, which generalize Baba's result. In the present paper some more results in this direction are proved. A module M is said to be completely almost self-injective, if for any two subfactors A, B of M, A is almost B-injective. A necessary and sufficient condition for a module M to be completely almost self-injective is given. Using this, it is proved that a Von Neumann ring R is completely almost right self-injective if and only if Rsoc(RR) is semi-simple and every minimal right ideal of R is injective.

Simple-direct-modules

ABSTRACTA right R-module M is called simple-direct-injective if, whenever, A and B are simple submodules of M with A≅B, and B⊆⊕M, then A⊆⊕M. Dually, M is called simple-direct-projective if, whenever, A and B are submodules of M with M∕A≅B⊆⊕M and B simple, then A⊆⊕M. In this paper, we continue our investigation of these classes of modules strengthening many of the established results on the subject. For example, we show that a ring R is uniserial (artinian serial) with J2(R) = 0 iff every simple-direct-projective right R-module is an SSP-module (SIP-module) iff every simple-direct-injective right R-module is an SIP-module (SSP-module).

Almost relative injective modules

The concept of a module $M$ being almost $N$-injective, where $N$ is some module, was introduced by Baba (1989). For a given module $M$, the class of modules $N$, for which $M$ is almost $N$-injective, is not closed under direct sums. Baba gave a necessary and sufficient condition under which a uniform, finite length module $U$ is almost $V$-injective, where $V$ is a finite direct sum of uniform, finite length modules, in terms of extending properties of simple submodules of $V$. Let $M$ be a uniform module and $V$ be a finite direct sum of indecomposable modules. Some conditions under which $M$ is almost $V$-injective are determined, thereby Baba's result is generalized. A module $M$ that is almost $M$-injective is called an almost self-injective module. Commutative indecomposable rings and von Neumann regular rings that are almost self-injective are studied. It is proved that any minimal right ideal of a von Neumann regular, almost right self-injective ring, is injective. This result is used to give an example of a von Neumann regular ring that is not almost right self-injective.

Simple-direct-injective modules

A module M over a ring is called simple-direct-injective if, whenever A and B are simple submodules of M with A≅B and B⊆⊕M, we have A⊆⊕M. Various basic properties of these modules are proved, and some well-studied rings are characterized using simple-direct-injective modules. For instance, it is proved that a ring R is artinian serial with Jacobson radical square zero if and only if every simple-direct-injective right R-module is a C3-module, and that a regular ring R is a right V-ring (i.e., every simple right R-module is injective) if and only if every cyclic right R-module is simple-direct-injective. The latter is a new answer to Fisher's question of when regular rings are V-rings [8].