Double affine Hecke algebras,conformal coinvariants and Kostka polynomials

We study a class of representations called ‘calibrated representations’ of the rational and trigonometric double affine Hecke algebras of type ${\mathit{GL}}_n$. We give a realization of calibrated irreducible modules as spaces of coinvariants constructed from integrable modules over the affine Lie algebra ${\stackrel{?}{\mathfrak{gl}}}_m$. We also give a character formula of these irreducible modules in terms of a generalization of Kostka polynomials. These results are conjectured by Arakawa, Suzuki and Tsuchiya based on the conformal field theory. The proofs using recent results on the representation theory of the double affine Hecke algebras will be presented in the forthcoming papers. To cite this article: T. Suzuki, C. R. Acad. Sci. Paris, Ser. I 343 (2006).     

On the coinvariants of modular representations of cyclic groups of prime order

We consider the ring of coinvariants for modular representations of cyclic groups of prime order. For all cases for which explicit generators for the ring of invariants are known, we give a reduced Gröbner basis for the Hilbert ideal and the corresponding monomial basis for the coinvariants. We also describe the decomposition of the coinvariants as a module over the group ring. For one family of representations, we are able to describe the coinvariants despite the fact that an explicit generating set for the invariants is not known. In all cases our results confirm the conjecture of Harm Derksen and Gregor Kemper on degree bounds for generators of the Hilbert ideal. As an incidental result, we identify the coefficients of the monomials appearing in the orbit product of a terminal variable for the three-dimensional indecomposable representation.     

Adjoint lifts and modular endomorphism algebras

We prove that the ramification of the endomorphism algebra of the Grothendieck motive attached to a non-CM cuspform of weight two or more is completely determined by the slopes of the adjoint lift of this form, when the slopes are finite. We treat all places of good and bad reduction, answering a question of Ribet about the Brauer class of the endomorphism algebra in the finite slope case.     

Identifications in modular group algebras

Let G be a group, S a subgroup of G, and F a field of characteristic p. We denote the augmentation ideal of the group algebra FG by ω(G). The Zassenhaus-Jennings-Lazard series of G is defined by D_n(G)=G∩(1+ωⁿ(G)). We give a constructive proof of a theorem of Quillen stating that the graded algebra associated with FG is isomorphic as an algebra to the enveloping algebra of the restricted Lie algebra associated with the D_n(G). We then extend a theorem of Jennings that provides a basis for the quotient ωⁿ(G)/ωⁿ⁺¹(G) in terms of a basis of the restricted Lie algebra associated with the D_n(G). We shall use these theorems to prove the main results of this paper. For G a finite p-group and n a positive integer, we prove that G∩(1+ω(G)ωⁿ(S))=D_n+1(S) and G∩(1+ω²(G)ωⁿ(S))=D_n+2(S)D_n+1(S∩D₂(G)). The analogous results for integral group rings of free groups have been previously obtained by Gruenberg, Hurley, and Sehgal.     

Extended canonical algebras and Fuchsian singularities

The authors introduce a new class of finite dimensional algebras called extended canonical, and determine the shape of their derived categories. Extended canonical algebras arise from a canonical algebra ?? by onepoint extension or coextension by an indecomposable projective module. Our main results concern the case of negative Euler characteristic of the corresponding weighted projective line ${\mathbb{X}}$ ; more specifically we establish, for a base field of arbitrary characteristic, a link to the Fuchsian singularity R of ${\mathbb{X}}$ which for the base field of complex numbers is isomorphic to an algebra of automorphic forms. By means of a recent result of Orlov we show that the triangulated category of the graded singularities of R (in the sense of Buchweitz and Orlov) admits a tilting object whose endomorphism ring is the corresponding extended canonical algebra. Of particular interest are those cases where the attached Coxeter transformation has spectral radius one. A K-theoretic analysis then shows that this happens exactly for 38 cases including Arnold??s 14 exceptional unimodal singularities. The paper is related to recent independent work by Kajiura, Saito and Takahashi.     

Extended Rees algebras and mixed multiplicities

Partially supported by the general research fund at the University of Kansas     

Lattices with modular identity and Lie algebras

The classification of Lie algebras over a principal ideal ring, the lattice of whose subalgebras satisfies a modular identity, is given.Translated from Itogi Nauki i Tekhniki, Sovremennye Problemy Matematiki, Noveishie Dostizheniya, Vol. 26, pp. 213–257, 1985.     

Generalized Kac-Moody algebras and the modular functionj

Research at MSRI supported in part by NSF Grant #DMS 9022140     

Many-sorted algebras in congruence modular varieties

We present several basic results on many-sorted algebras, most of them only valid in congruence modular varieties. We describe a connection between the properties of many-sorted varieties and those of varieties of one sort and give some results on functional completeness, the commutator and Abelian algebras.Presented by H. P. Gumm.     

Unitary units in modular group algebras

Letp be a prime,K a field of characteristicp, G a locally finitep-group,KG the group algebra, andV the group of the units ofKG with augmentation 1. The anti-automorphismg→g ⁻¹ ofG extends linearly toKG; this extension leavesV setwise invariant, and its restriction toV followed byv→v ⁻¹ gives an automorphism ofV. The elements ofV fixed by this automorphism are calledunitary; they form a subgroup. Our first theorem describes theK andG for which this subgroup is normal inV. For each elementg inG, let denote the sum (inKG) of the distinct powers ofg. The elements 1+(g-1) withh,hεG are thebicyclic units ofKG. Our second theorem describes theK andG for which all bicyclic units are unitary. Research partly supported by the Hungarian National Foundation for Scientific Research grant no. T4265. The second author is indebted to the ‘Universitas’ Foundation and the Lajos Kossuth University of Debrecen, Hungary, for warm hospitality and generous support during the period when this work began. This article was processed by the authors using the Springer-Verlag T_EX mamath macro package 1990.     

On invariants of modular free Lie algebras

Suppose that L(X) is a free Lie algebra of finite rank over a field of positive characteristic. Let G be a nontrivial finite group of homogeneous automorphisms of L(X). It is known that the subalgebra of invariants H = L ^G is infinitely generated. Our goal is to describe how big its free generating set is. Let Y = è_{n = 1}^￥ Y_n Y = \bigcup\limits_{n = 1}^\infty {{Y_n}} be a homogeneous free generating set of H, where elements of Y _n are of degree n with respect to X. We describe the growth of the generating function of Y and prove that |Y _n | grow exponentially.     

Basic subgroups in modular abelian group algebras

Suppose F is a perfect field of char F = p ≠ 0 and G is an arbitrary abelian multiplicative group with a p-basic subgroup B and p-component G _p . Let FG be the group algebra with normed group of all units V(FG) and its Sylow p-subgroup S(FG), and let I _p (FG; B) be the nilradical of the relative augmentation ideal I(FG; B) of FG with respect to B. The main results that motivate this article are that 1 + I _p (FG; B) is basic in S(FG), and B(1 + I _p (FG; B)) is p-basic in V(FG) provided G is p-mixed. These achievements extend in some way a result of N. Nachev (1996) in Houston J. Math. when G is p-primary. Thus the problem of obtaining a (p-)basic subgroup in FG is completely resolved provided that the field F is perfect. Moreover, it is shown that G _p (1 + I _p (FG; B))/G _p is basic in S(FG)/G _p , and G(1 + I _p (FG; B))/G is basic in V(FG)/G provided G is p-mixed. As consequences, S(FG) and S(FG)/G _p are both starred or divisible groups. All of the listed assertions enlarge in a new aspect affirmations established by us in Czechoslovak Math. J. (2002), Math. Bohemica (2004) and Math. Slovaca (2005) as well.     

格蕴涵代数的扩展LI-理想

LI-理想是研究格蕴涵代数结构特征的一个重要的工具性概念.综合运用代数学与逻辑学的方法和原理对格蕴涵代数的LI-理想理论作进一步深入研究.首先,引入格蕴涵代数L的LI-理想A关于L的子集M的扩展LI-理想及稳定LI-理想概念并考察它们的基本性质.其次,讨论了L的几类扩展LI-理想集的格论特征.证明了L的关于一个给定子集M?L的稳定LI-理想全体之集S(M)与L的一个LI-理想A关于任意子集M?L的扩展LI-理想全体之集EA均构成完备Heyting代数的结论.再次,给出了商格蕴涵代数和乘积格蕴涵代数的扩展LI-理想的若干性质.最后,借助于L的扩展LI-理想之特性获得了L的ILI-理想的若干等价刻画.