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11 votes

Why are operads useful?

One reason that operads are used is in obstruction theory. … However, it is difficult to attack such problems outside specific circumstances without using operads. (Perhaps someone else knows of methods that don't implicitly use operads; I don't.) …
Tyler Lawson's user avatar
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17 votes
Accepted

Is it possible to construct an action of an $E_\infty$ operad on $BU$ that respects filtrati...

Unfortunately there is no such filtration. At first, this looks very similar (but not as strong as) asking for a map of $E_\infty$ spaces $\coprod BU(n) \to BU$ which would become a splitting map $ku …
Tyler Lawson's user avatar
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6 votes

Pontryagin product from an operad

You can do that. If an operad O acts on a space X, then the structure maps O(n) x Xn -> X induce homology operations H*O(n) ⊗ H*(X)⊗n -> H*(X). In particular, any path component in O(2) produces …
Tyler Lawson's user avatar
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11 votes
Accepted

understanding the definition of $\infty$-operad of module objects

I know this question is a little old but I just came across it. Roughly, as you say, from this data you get an object $v$ of $O^\otimes$ and an algebra $A$ of $Alg_{/O}(C)$. However, you also get an …
Tyler Lawson's user avatar
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4 votes

Is there a concise description of the $\infty$-category $\mathrm{Mod}_A^\mathcal{O}(\mathcal...

Spaces and classical (single-object) operads are the easiest example. …
Tyler Lawson's user avatar
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4 votes
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Topological category of topological monoids / operads

(Similar remarks apply to operads.) …
Tyler Lawson's user avatar
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3 votes
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Graded commutativity of the $n$th Browder bracket

Both papers choose a normalization that is different from yours: they define $$ [a,b] = (-1)^{na+1} s(a \otimes b). $$ This is definition 5.7 in Cohen's paper that you mentioned. The reason for this …
Tyler Lawson's user avatar
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10 votes
Accepted

Reference Request: Grouplike Algebras over the little $n$-cubes operad are $n$-fold loop spaces

May gave a proof in the case $n = \infty$ in this followup paper to "Geometry of iterated loop spaces," which relies on knowing that a certain map (from a free algebra on $X$ to the free infinite loop …
Tyler Lawson's user avatar
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6 votes
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Is there a model structure for S-modules such that cofibrant operad-algebras forget to cofib...

Here is something that I think is reasonably difficult to get around. As you observe, the unit is the initial object of commutative monoids, and so your request includes that the unit is cofibrant. Su …
Tyler Lawson's user avatar
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