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For questions about ring spectra (in homotopy theory).

4 votes

Has anyone seen a nice map of multiplicative cohomology theories?

An informal reference could be the diagram on page 2 of the lecture notes from my September 2000 lecture in Oberwolfach, where I discussed the chromatic red-shift conjecture.
John Rognes's user avatar
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8 votes
Accepted

What is the topological Hochschild cohomology of $\mathbb{F}_p$?

Let me write $HH^S(B) = THH(B) = B \wedge_{B^e} B$ for topological Hochschild homology, and $HH_S(B) = F_{B^e}(B, B)$ for topological Hochschild cohomology, where $B^e = B \wedge_S B^{op}$. For $B$ c …
John Rognes's user avatar
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2 votes
Accepted

Interesting "epimorphisms" of $E_\infty$-ring spectra

If $A$ is an $E_\infty$ ring spectrum and $i : A \to B$ is any map of $A_\infty = E_1$ ring spectra such that the multiplication $\mu : B \wedge_A B^{op} \to B$ is an equivalence, then $B \simeq LA$ w …
John Rognes's user avatar
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10 votes

Group of units of a ring spectrum vs of its connective cover

For symmetric ring spectra $R$ there is also a definition of the graded group of units, $GL_1^J(R)$, which retains information about the negative homotopy groups of $R$. See Sagave-Schlichtkrull, "Dia …
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