Realizability of Two-dimensional Linear Groups over Rings of Integers of Algebraic Number Fields

Given the ring of integers O _K of an algebraic number field K, for which natural numbers n there exists a finite group G???GL(n, O _K ) such that O _K G, the O _K -span of G, coincides with M(n, O _K ), the ring of (n?×?n)-matrices over O _K ? The answer is known if n is an odd prime. In this paper we study the case n?=?2; in the cases when the answer is positive for n?=?2, for n?=?2m there is also a finite group G???GL(2m, O _K ) such that O _K G?=?M(2m, O _K ).     

实二次代数整数环上的正定幺模格的分类

推广了Ｋｎｅｓｅｒ的邻格方法，研究了Ｚ［／ｄ］　　上的秩４ｎ判别式１的正定幺模种的邻格性质，完成了Ｚ［／３］上秩４的正定幺模格的分类．     

实二次代数整数环上的单位格的类数

用邻格方法及Siegelmass公式证明了实二次代数域Q(√d)上单位格种gen(In)n≥4)的类数h(In)=3当且仅当Q(√3):n=4;Q(√5);n=6;Q(√3);n=4;Q(√17):n=4.     

Types of Root Systems in Number Fields

We classify the types of root systems R in the rings of integers of number fields K such that the Weyl group W(R) lies in the group generated by Aut(K) and multiplications by the elements of K*.     

Small Skew Lattices in Rings

Given idempotents e and f in a ring R, if ef and fe are also idempotent, then e and f generate a skew lattice in R that splits, having order dividing 16. The skew Boolean algebra generated from e and f is also considered.     

Pure Skew Lattices in Rings

Given a ring $R$, let $S\subseteq R$ be a pure multiplicative band that is closed under the cubic join operation $x\nabla y = x+y+yx-xyx-yxy.$ We show that $\left( S,\cdot,\nabla\right) $ forms a pure skew lattice if and only if $S$ satisfies the polynomial identity $\left(xy-yx\right)^{2}z = z\left(xy-yx\right)^{2}$. We also examine properties of pure skew lattices in rings.     

Lattice-Ordered Matrix Rings Over the Integers

We show that the only compatible lattice order on a matrix ring over the integers for which the identity matrix is positive is (up to isomorphism) the usual, entrywise, lattice order. We also find a condition that guarantees that the only compatible lattice order on a matrix ring over the integers is formed by multiplying the positive cone of the usual, entrywise, lattice order by a matrix with positive entries. Using this condition, we show that such orders are the only compatible ones in the two-by-two case.     

Thue and Thue-Mahler Equations over Rings of Integers

A method is given to solve any Thue–Mahler equation whenthe coefficients and variables come from the ring of integersof a number field. The method involves using an algorithm forsolving an S-unit equation and a method of reducing the numberof exponential variables. The method is used to solve the equation      

Rings with Lattices of Idempotents

The central idempotents of any ring with identity form a Boolean algebra. This result is largely extended for rings with generalized commuting idempotents.     

Galois Structure of K-Groups of Rings of Integers

N/Kbe a Galois extension of number fields with finite Galois group G.We describe a new approach for constructing invariants of the G-module structure of the K groups of the ring of integers of N in the Grothendieck group of finitely generated projective Z[G]modules. In various cases we can relate these classes, and their function field counterparts, to the root number class of Fröhlich and Cassou-Noguès.     

Lattices of Radicals of Involution Rings

A lattice-theoretic approach to the radical theory of rings was initiated by Snider. In the current paper, we extend this approach to the radical theory of involution rings. We show that the classes of hereditary radicals, radicals satisfying ADS and invariant radicals form complete sublattices of the lattice of all radicals of involution rings. We show that certain sublattices are isomorphic to sublattices of the lattice of radicals of rings. We characterize the atoms of certain lattices of radicals of involution rings.1991 Mathematics Subject Classification: 16W10, 16N99, 06B99     

Multiplicative Invariants of Root Lattices

We describe the multiplicative invariant algebras of the root lattices of all irreducible root systems under the action of the Weyl group. In each case, a finite system of fundamental invariants is determined and the class group of the invariant algebra is calculated. In some cases, a presentation and a Hironaka decomposition of the invariant algebra is given.     

Witt Rings of Global Fields

Abstract

In 1989 DeMeyer et al. (DeMeyer,F.,Harrison,D.,Miranda,R. (1989). Quadratic forms over ? and Galois extensions of commutative rings. Mem. Amer. Math. Soc. 77(394)) described the Witt ring of the rational number field in terms of Hilbert symbols. The same has been done by the first author for global function fields. The aim of this paper is to obtain a similar result for any global field.     

Non-Unique Factorization of Polynomials Over Residue Class Rings of the Integers

We investigate non-unique factorization of polynomials in ? _{p ⁿ} [x] into irreducibles. As a Noetherian ring whose zero-divisors are contained in the Jacobson radical, ? _{p ⁿ} [x] is atomic. We reduce the question of factoring arbitrary nonzero polynomials into irreducibles to the problem of factoring monic polynomials into monic irreducibles. The multiplicative monoid of monic polynomials of ? _{p ⁿ} [x] is a direct sum of monoids corresponding to irreducible polynomials in ? _p [x], and we show that each of these monoids has infinite elasticity. Moreover, for every m ∈ ?, there exists in each of these monoids a product of 2 irreducibles that can also be represented as a product of m irreducibles.     

I-Radicals,Their Lattices,and Some Classes of Rings

We describe some I-radicals in the categories of modules over semilocal rings. We give a characterization of rings over which the set of I-radicals coincides with the set of hereditary idempotent radicals. We prove that the lattices of I-radicals in the categories of modules over Morita-equivalent rings are isomorphic.     

Nonrigidity Degrees of Root Lattices and their Duals

The nonrigidity degree of a lattice L, nrdL, is the dimension of the L-type domain to which L belongs. We complete here the table of nrd's of all irreducible root lattices and their duals (we give also the minimal rank of their Delaunay polytopes). In particular, the hardest remaining case of D _n *, and the case of E ₇* are decided. As any root lattice is a direct sum of some irreducible ones, its nrd is a sum of nrd's of the summands. We describe explicitly the L-type domain , n 4. For n odd, it is a nonsimplicial, polyhedral, open cone of dimension n. For n even, it is one-dimensional, i.e. any D _2m * corresponds to an edge form.     

Fractals and Number Systems in Real Quadratic Number Fields

In this paper we compute the box counting dimension of sets, that are related to number systems in real quadratic number fields. The sets under discussion are so-called graph-directed self affine sets. Contrary to the case of self similar sets, for self affine sets there does not exist a general theory for the determination of the box counting dimension. Thus we are forced to construct the covers, needed for its calculation, directly. This revised version was published online in July 2006 with corrections to the Cover Date.