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The Hochschild cohomology of a closed manifold

Yves Felix, Jean-Claude Thomas, Micheline Vigué-Poirrier (2004)

Publications Mathématiques de l'IHÉS

Let M be a closed orientable manifold of dimension dand 𝒞 * ( M ) be the usual cochain algebra on M with coefficients in a fieldk. The Hochschild cohomology of M, H H * ( 𝒞 * ( M ) ; 𝒞 * ( M ) ) is a graded commutative and associative algebra. The augmentation map ε : 𝒞 * ( M ) 𝑘 induces a morphism of algebras I : H H * ( 𝒞 * ( M ) ; 𝒞 * ( M ) ) H H * ( 𝒞 * ( M ) ; 𝑘 ) . In this paper we produce a chain model for the morphism I. We show that the kernel of I is a nilpotent ideal and that the image of I is contained in the center of H H * ( 𝒞 * ( M ) ; 𝑘 ) , which is in general quite small. The algebra H H * ( 𝒞 * ( M ) ; 𝒞 * ( M ) ) is expected to be isomorphic...

The image of the natural homomorphism of Witt rings of orders in a global field

Beata Rothkegel (2013)

Acta Arithmetica

Let R be a Dedekind domain whose field of fractions is a global field. Moreover, let 𝓞 < R be an order. We examine the image of the natural homomorphism φ : W𝓞 → WR of the corresponding Witt rings. We formulate necessary and sufficient conditions for the surjectivity of φ in the case of all nonreal quadratic number fields, all real quadratic number fields K such that -1 is a norm in the extension K/ℚ, and all quadratic function fields.

The Novikov conjecture for linear groups

Erik Guentner, Nigel Higson, Shmuel Weinberger (2005)

Publications Mathématiques de l'IHÉS

Let K be a field. We show that every countable subgroup of GL(n,K) is uniformly embeddable in a Hilbert space. This implies that Novikov’s higher signature conjecture holds for these groups. We also show that every countable subgroup of GL(2,K) admits a proper, affine isometric action on a Hilbert space. This implies that the Baum-Connes conjecture holds for these groups. Finally, we show that every subgroup of GL(n,K) is exact, in the sense of C*-algebra theory.

The Roquette category of finite p -groups

Serge Bouc (2015)

Journal of the European Mathematical Society

Let p be a prime number. This paper introduces the Roquette category p of finite p -groups, which is an additive tensor category containing all finite p -groups among its objects. In p , every finite p -group P admits a canonical direct summand P , called the edge of P . Moreover P splits uniquely as a direct sum of edges of Roquette p -groups, and the tensor structure of p can be described in terms of such edges. The main motivation for considering this category is that the additive functors from p to...

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