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Suppose I have a bounded chain complex $C_{\ast}$ over the group ring $\mathbb{Z}G$ for a finite group $G$. In topology we are usually in a situation when $C_{\ast}$ is a complex of projective modules. Now for any other $\mathbb{Z}G$-module $M$ homology of the complex $C_{\ast} \otimes_{\mathbb{Z}G} M$ can be computed using universal coefficient spectral sequence (UCSS). In fact UCSS is the hyperhomology spectral sequence and luckily in this case hyperhomology groups $\mathbb{H}_{\ast}(C_{\ast}, M)$ are equal to ordinary homology of $C_{\ast} \otimes_{\mathbb{Z}G} M$.

When $C_{\ast}$ is a chain complex of modules which are not flat, then we still have hyperhomology spectral sequence, however in this case hyperhomology is usually different from homology of $C_{\ast} \otimes_{\mathbb{Z}G} M$. So my question is the following: are there any theorems which give us any kind of direct relation between homology of $C_{\ast}$ and homology of $C_{\ast} \otimes_{\mathbb{Z}G} M$? For example is there any generalisation of UCSS, which allows to compute $H_{\ast}(C_{\ast} \otimes_{\mathbb{Z}G} M)$?

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  • $\begingroup$ What do we get if we simply use the projective resolution of M? $\endgroup$
    – user43326
    Commented Jul 17, 2014 at 6:55
  • $\begingroup$ You should not expect such a thing to exist; spectral sequences want to exist in derived categories and converge to a derived tensor. However, in my experience you usually want to compute the tensor over Z using the diagonal G-action, not the tensor over Z[G], and then you only need one of C_* or M to be flat over Z. $\endgroup$
    – Mark Hovey
    Commented Jul 17, 2014 at 11:37

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