On the Cohomology Sequence in a Semiabelian Category

In a semiabelian category, a strictly exact sequence 0→A→B→C→0 of cochain complexes gives rise to the cohomology sequence ...→H ⁿ(A) →H ⁿ(B)→ H ⁿ(C)→ H ⁿ⁺¹ (A) →.... We study conditions for exactness of the homology sequence at a given term.     

Relative Group Cohomology and The Orbit Category

Let G be a finite group and ? be a family of subgroups of G closed under conjugation and taking subgroups. We consider the question whether there exists a periodic relative ?-projective resolution for ? when ? is the family of all subgroups H ≤ G with rk H ≤ rkG ? 1. We answer this question negatively by calculating the relative group cohomology ?H*(G, 𝔽₂) where G = ?/2 × ?/2 and ? is the family of cyclic subgroups of G. To do this calculation we first observe that the relative group cohomology ?H*(G, M) can be calculated using the ext-groups over the orbit category of G restricted to the family ?. In second part of the paper, we discuss the construction of a spectral sequence that converges to the cohomology of a group G and whose horizontal line at E ₂ page is isomorphic to the relative group cohomology of G.     

Directions for the Long Exact Cohomology Sequence in Moore Categories

A new method for realizing the first and second order cohomology groups of an internal abelian group in a Barr-exact category was introduced by Bourn (Cahiers Topologie Géom Différentielle Catég XL:297–316, 1999; J Pure Appl Algebra 168:133–146, 2002). The main role, in each level, is played by a direction functor. This approach can be generalized to any level n and produces a long exact cohomology sequence. By applying this method to Moore categories we show that they represent a good context for non-abelian cohomology, in particular for the Baer Extension Theory.      

On the Cohomology of Associative Superalgebras

§ 1.ＢａｓｉｃＣｏｎｃｅｐｔｓ　Ｔｈｒｏｕｇｈｏｕｔｔｈｉｓｐａｐｅｒ,Ａ =Ａ0 Ａ1ｉｓａｌｗａｙｓａｓｓｕｍｅｄｔｏｂｅａｎａｓｓｏｃｉａｔｉｖｅｓｕｐｅｒａｌｇｅｂｒａｗｉｔｈｕｎｉｔｙｏｖｅｒａｆｉｌｅｄＦ ,ａｎｄＬ =Ｌ0 Ｌ1ａＬｉｅｓｕｐｅｒａｌｇｅｂｒａｏｖｅｒＦ .Ｉｆ |ｘ|ｏｃｃｕｒｓｉｎｓｏｍｅｅｘｐｒｅｓｓｉｏｎ ,ｔｈｅｎｉｔｉｓａｓｓｕｍｅｄｔｈａｔｘｉｓａｈｏｍｏｇｅｎｅｏｕｓｅｌｅｍｅｎｔａｂｏｕｔＺ2 ｇｒａｄｅｄａｎｄ |ｘ|ｄｅｎｏｔｅｓｔｈｅＺ2 ｇｒａｄｅｄｄｅｇｒｅｅ…     

On Finite-Valued Cohomology Theories

In this paper, we describe cohomology theories constructed on the category of pairs of topological spaces and continuous maps and based on finite-valued cochains with coefficients in abelian group.     

On the Karoubi Filtration of a Category

Let be an -filtered category in the sense of Karoubi. This is the categorical analogue of an ideal in a ring . Pedersen and Weibel constructed a fibration of K-theory spectra associated with the sequence . We present a new easier proof based on Waldhausen' generic fibration.     

On the Leibniz Cohomology of Vector Fields

Gelfand and Fuks have studied the cohomology of the Lie algebra of vector fields on a manifold. In this article, we generalize their main tools to compute the Leibniz cohomology, by extending the two spectral sequences associated to the diagonal and the order filtration. In particular, we determine some new generators for the diagonal Leibniz cohomology of the Lie algebra of vector fields on the circle.     

On the Cohomology of Hermitian Symmetric Spaces

A formula for the value of a power of a two-dimensional cohomology class of a simply connected compact Hermitian symmetric space M at an arbitrary homology class of this space is derived.     

On the Cohomology of Relative Hopf Modules

Let H be a Hopf algebra over a field k, and A an H-comodule algebra. The categories of comodules and relative Hopf modules are then Grothendieck categories with enough injectives. We study the derived functors of the associated Hom functors, and of the coinvariants functor, and discuss spectral sequences that connect them. We also discuss when the coinvariants functor preserves injectives.     

On the Hochschild Cohomology of Triangular Algebras

Abstract

In order to study the Hochschild cohomology of an n-triangular algebra 𝒯 _n , we construct a spectral sequence, whose terms are parametrized by the length of the trajectories of the quiver associated with 𝒯 _n , and which converges to the Hochschild cohomology of 𝒯 _n . We describe explicitly its components and its differentials which are sums of cup products. In case n = 3 we study some properties of the differential at level 2. We give some examples of use of the spectral sequence and recover formulas for the dimension of the cohomology groups of particular cases of triangular algebras.     

On Carleman formulas for the Dolbeault Cohomology

We discuss the Cauchy problem for the Dolbeault cohomology in a domain of C ⁿ with data on a part of the boundary. In this setting we introduce the concept of a Carleman function which proves useful in the study of uniqueness. Apart from an abstract framework we show explicit Carleman formulas for the Dolbeault cohomology. To the memory of Lamberto Cattabriga     

On the Cohomology of Configuration Spaces on Surfaces

The integral cohomology rings of the configuration spaces ofn-tuples of distinct points on arbitrary surfaces (not necessarilyorientable, not necessarily compact and possibly with boundary)are studied. It is shown that for punctured surfaces the cohomologyrings stabilize as the number of points tends to infinity, similarlyto the case of configuration spaces on the plane studied byArnold, and the Goryunov splitting formula relating the cohomologygroups of configuration spaces on the plane and punctured planeto arbitrary punctured surfaces is generalized. Moreover, onthe basis of explicit cellular decompositions generalizing theconstruction of Fuchs and Vainshtein, the first cohomology groupsfor surfaces of low genus are given.     

On the Algebraic Cohomology of Real Algebraic M-Varieties

For a real algebraic M-variety X, the canonical homomorphism of the algebraic cohomology group of the set of real points into the algebraic cohomology group of the set of complex points $$\varrho _k :H_{alg}^k (X(\mathbb{R}),\mathbb{Z}/2) \to H_{alg}^{2k} (X(\mathbb{C}),\mathbb{Z}/2)$$ is considered. This homomorphism agrees with the cycle mappings. Estimates for the dimension of the kernel of this homomorphism are given.