Exact sequences in homology of multiplicative Lie rings and a new version of Stallings' theorem

We show that the non-abelian tensor product of nilpotent, solvable and Engel multiplicative Lie rings is nilpotent, solvable and Engel, respectively. The six term exact sequence in homology of multiplicative Lie rings is obtained. We also prove a new version of Stallings' theorem.     

Homology of generalized partition posets

We define a family of posets of partitions associated to an operad. We prove that the operad is Koszul if and only if the posets are Cohen-Macaulay. On the one hand, this characterization allows us to compute completely the homology of the posets. The homology groups are isomorphic to the Koszul dual cooperad. On the other hand, we get new methods for proving that an operad is Koszul.     

Homology of -types and Hopf type formulas

The tripleability of the category of crossed n-cubes is studied. The leading cotriple homology of these homotopy (n+1)-types is investigated, describing it as Hopf type formulas.     

Local rings whose multiplicative group is nilpotent

We prove that the upper central chain of the multiplicative group of a local ring R coincides with the chain of the multiplicative group of terms of the upper central chain of the associated Lie ring of R. Received: 30 January 2002     

A geometric decomposition of spaces into cells of different types II: Homology theory

We develop the homology theory of CW(A)-complexes, generalizing the classical cellular homology theory for CW-complexes. A CW(A)-complex is a topological space which is built up out of cells of a certain core A.     

Heights of algebraic numbers modulo multiplicative group actions

Given a number field K and a subgroup G⊂K^∗ of the multiplicative group of K, Silverman defined the G-height H(θ;G) of an algebraic number θ as

     

Cohomology rings of multiplicative fibrations

Let p be an odd prime. Let be the fibre space induced from an H-map where K is a generalized Eilenberg MacLane space and X is a simply connected H-space. Such spaces occur frequently in Postnikov towers and connective covers. In this paper, we compute the mod p cohomology of as a ring. The ring depends on the structure of imf^* and the structure of subkerf^* as modules over the Steenrod algebra.     

The Green rings of pointed tensor categories of finite type

In this paper, we compute the Clebsch–Gordan formulae and the Green rings of connected pointed tensor categories of finite type.     

On the relative homology of cleft extensions of rings and abelian categories

We study the relative homological behaviour of the omnipresent class of cleft extensions of abelian categories. This class of extensions is a natural generalization of the trivial extensions studied in detail by Fossum, Griffith and Reiten and by Palmer and Roos. We apply our results to the relative homology of cleft extensions of rings.     

On Galois cohomology of semisimple groups over local and global fields of positive characteristic

We treat a case that was omitted from consideration in our article [2] in Math Zeit, 2007.     

The operad Lie is free

We show that the operad Lie is free as a non-symmetric operad. Then we study the generating series counting the operadic generators. We find a recursive formula for the coefficients of the series and show that the asymptotic density of the operadic generators is 1/e.     

Lie properties of symmetric elements in group rings II

Let F be a field of characteristic different from 2, and G a group with involution ∗. Write (FG)⁺ for the set of elements in the group ring FG that are symmetric with respect to the induced involution. Recently, Giambruno, Polcino Milies and Sehgal showed that if G has no 2-elements, and (FG)⁺ is Lie nilpotent (resp. Lie n-Engel), then FG is Lie nilpotent (resp. Lie m-Engel, for some m). Here, we classify the groups containing 2-elements such that (FG)⁺ is Lie nilpotent or Lie n-Engel.     

Motivic zeta functions of infinite-dimensional Lie algebras

The paper shows how to associate a motivic zeta function with a large class of infinite dimensional Lie algebras. These include loop algebras, affine Kac-Moody algebras, the Virasoro algebra and Lie algebras of Cartan type. The concept of a motivic zeta functions provides a good language to talk about the uniformity in p of local p-adic zeta functions of finite dimensional Lie algebras. The theory of motivic integration is employed to prove the rationality of motivic zeta functions associated to certain classes of infinite dimensional Lie algebras.     

Resolutions of Stanley-Reisner rings and Alexander duality

Associated to any simplicial complex Δ on n vertices is a square-free monomial ideal I_Δ in the polynomial ring A = k[x₁, …, x_n], and its quotient k[Δ] = A/I_Δ known as the Stanley-Reisner ring. This note considers a simplicial complex Δ^* which is in a sense a canonical Alexander dual to Δ, previously considered in [1, 5]. Using Alexander duality and a result of Hochster computing the Betti numbers dim_k Tor_i^A (k[Δ],k), it is shown (Proposition 1) that these Betti numbers are computable from the homology of links of faces in Δ^*. As corollaries, we prove that I_Δ has a linear resolution as A-module if and only if Δ^* is Cohen-Macaulay over k, and show how to compute the Betti numbers dim_k Tor_i^A (k[Δ],k) in some cases where Δ^* is wellbehaved (shellable, Cohen-Macaulay, or Buchsbaum). Some other applications of the notion of shellability are also discussed.     

Stacks of Algebras and Their Homology

For any increasing function which takes only finitely many distinct values, a connected finite dimensional algebra is constructed, with the property that for all ; here is the -generated finitistic dimension of . The stacking technique developed for this construction of homological examples permits strong control over the higher syzygies of -modules in terms of the algebras serving as layers. The first author was supported in part by a fellowship stipend from the National Physical Science Consortium and the National Security Agency. The second author was partially supported by a grant from the National Science Foundation.     

Jordan-Hölder, modularity and distributivity in non-commutative algebra

A study of lattices of subgroups or subrings adequate for non-commutative homological algebra can be pursued in a setting of weakly exact categories, which extend the Puppe-exact ones [D. Puppe, Korrespondenzen in abelschen Kategorien, Math. Ann. 148 (1962) 1-30; B. Mitchell, Theory of Categories, Academic Press, New York, 1965; P. Freyd, A. Scedrov, Categories, Allegories, North-Holland Publishing Co., Amsterdam, 1990] and the semi-abelian ones [G. Janelidze, L. Márki, W. Tholen, Semi-abelian categories, J. Pure Appl. Algebra 168 (2002) 367-386; F. Borceux, A survey of semi-abelian categories, in: Galois Theory, Hopf Algebras, and Semiabelian Categories, in: Fields Inst. Commun., vol. 43, Amer. Math. Soc., Providence, RI, 2004, pp. 27-60; F. Borceux, D. Bourn, Mal’cev, Protomodular, homological and semi-abelian categories, in: Mathematics and its Applications, vol. 566, Kluwer Academic Publishers, Dordrecht, 2004], and are essentially based on a notion of γ-category introduced by Burgin [M.S. Burgin, Categories with involution and correspondences in γ-categories, Tr. Mosk. Mat. Obs. 22 (1970) 161-228; Trans. Moscow Math. Soc. 22 (1970) 181-257]. In this context, subobjects form w-modular w-lattices, equipped with a normality relation. The free w-modular w-lattice generated by two chains with normality conditions is determined and proved to be weakly distributive, by a construction inspired by the well-known Birkhoff theorem for free modular lattices [G. Birkhoff, Lattice Theory, 3rd ed., in: Amer. Math. Soc. Coll. Publ., vol. 25, 1973]. We show that this theorem is relevant for the study of double filtrations, much in the same way as the Birkhoff theorem in the commutative case; similarly, it should be of use in the study of spectral sequences.     

A Krull-Schmidt theorem for one-dimensional rings of finite Cohen-Macaulay type

This paper determines when the Krull-Schmidt property holds for all finitely generated modules and for maximal Cohen-Macaulay modules over one-dimensional local rings with finite Cohen-Macaulay type. We classify all maximal Cohen-Macaulay modules over these rings, beginning with the complete rings where the Krull-Schmidt property is known to hold. We are then able to determine when the Krull-Schmidt property holds over the non-complete local rings and when we have the weaker property that any two representations of a maximal Cohen-Macaulay module as a direct sum of indecomposables have the same number of indecomposable summands.     

Homology of dihedral quandles

We solve the conjecture by R. Fenn, C. Rourke and B. Sanderson that the rack homology of dihedral quandles satisfies for p odd prime [T. Ohtsuki, Problems on invariants of knots and 3-manifolds, Geom. Topol. Monogr. 4 (2002) 377-572, Conjecture 5.12]. We also show that contains Z_p for n≥3. Furthermore, we show that the torsion of is annihilated by 3. We also prove that the quandle homology contains Z_p for p odd prime. We conjecture that for n>1 quandle homology satisfies: , where f_n are “delayed” Fibonacci numbers, that is, f_n=f_n−1+f_n−3 and f(1)=f(2)=0,f(3)=1. Our paper is the first step in approaching this conjecture.