English

Mod-2 (co)homology of an abelian group

K-Theory and Homology 2022-01-19 v5 Algebraic Topology

Abstract

It is known that for a prime p2p\ne 2 there is the following natural description of the homology algebra of an abelian group H(A,Fp)Λ(A/p)Γ(pA)H_*(A,\mathbb F_p)\cong \Lambda(A/p)\otimes \Gamma({}_pA) and for finitely generated abelian groups there is the following description of the cohomology algebra of H(A,Fp)Λ((A/p))Sym((pA)).H^*(A,\mathbb F_p)\cong \Lambda((A/p)^\vee)\otimes {\sf Sym}(({}_pA)^\vee). We prove that there are no such descriptions for p=2p=2 that `depend' only on A/2A/2 and 2A{}_2A but we provide natural descriptions of H(A,F2)H_*(A,\mathbb F_2) and H(A,F2)H^*(A,\mathbb F_2) that `depend' on A/2,A/2, 2A{}_2A and a linear map β~:2AA/2.\tilde \beta:{}_2A\to A/2. Moreover, we prove that there is a filtration by subfunctors on Hn(A,F2)H_n(A,\mathbb F_2) whose quotients are Λn2i(A/2)Γi(2A)\Lambda^{n-2i}(A/2)\otimes \Gamma^i({}_2A) and that for finitely generated abelian groups there is a natural filtration on Hn(A,F2)H^n(A,\mathbb F_2) whose quotients are Λn2i((A/2))Symi((2A)). \Lambda^{n-2i}((A/2)^\vee)\otimes {\sf Sym}^i(({}_2A)^\vee).

Keywords

Cite

@article{arxiv.1810.12728,
  title  = {Mod-2 (co)homology of an abelian group},
  author = {Sergei O. Ivanov and Anatolii Zaikovskii},
  journal= {arXiv preprint arXiv:1810.12728},
  year   = {2022}
}