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In the stable homotopy category a map of spectra $f\colon X \rightarrow Y$ is called phantom is the induced map between the associated homology theories $X_* \rightarrow Y_*$ is zero, it is know that there are non-trivial phantom maps and these have been treated extensively. The most immediate reference I can think of is the paper "Phantom maps and homology theories" by Christensen and Strickland.

I was wondering if this was the case even in equivariant stable homotopy theory: i.e. suppose $G$ is a group, $f\colon X \rightarrow Y$ is a morphisms of $G$-spectra and for all the subgroups $H \leq G$ we have $\pi_*^H(f)\colon \pi_*^H(X)\rightarrow \pi_*^H(Y)$ is trivial. Do you have any reference for a study of this kind of maps? Do the results in the non-equivariant scenario generalize without any complication?

Also, it would be interesting to see what is their relationship with the maps $f$ such that $\Phi^H(f)$ is zero, where $\Phi^H$ indicates the geometric fixed points.

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    $\begingroup$ what do you mean "even" ? Take $G=e$, and you get your good-old phantom maps, or for any $G$, inducing up a phantom map gives you a phantom map as well. Generally you should expect the equivariant situation to be more complicated not less. $\endgroup$ Commented Nov 9, 2021 at 16:34
  • $\begingroup$ I mean if these equivariant phantom maps were extensively studied as well. "Even" referred to "studied" in the previous paragraph. A posteriori I added the sentence with the mention to Chirstensen and Strickland and I realize now that it makes the reference less clear. Anyway, my point is: this idea of defining and examining phantom maps in the equivariant setting cannot be a novelty, but I cannot find a paper or book discussing about it. $\endgroup$
    – N.B.
    Commented Nov 10, 2021 at 10:44

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