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The classifying space BG of a group G classifies principal G-bundles, in that homotopy classes of maps [X, BG] are naturally identified with isomorphism classes of principal G-bundles P ⭢ X.
4
votes
Accepted
Group completion of $E_k$-algebras
Group completion and the answer to your questions (for $k\geq 2$) are probaby best understood homologically. An ancient definition is that a map $X\rightarrow Y$ of homotopy commutative $H$-spaces …
5
votes
Accepted
configuration space and iterated loop space
$C_n(X)$ is not a monoid in any natural way; I never said it was. And the target $\Omega^n\Sigma^n X$ of $\alpha_n$ has $n$ different loop products. The question is not meaningful as posed. Neverthe …
9
votes
Accepted
Classifying space for fibrations with Eilenberg-MacLane space as fibers
There is a very careful analysis of this question in Lemma 3.4.2, page 57, of More Concise Algebraic Topology, by Kate Ponto and myself. Assuming that $E$ and $B$ are connected, a fibration $E\longrig …
10
votes
Accepted
A fibration of classifying spaces
This is an edited extract from a book in preparation (Bruner, Catanzaro, May)
tentatively titled Characteristic Classes and is therefore overlong for an
answer. This is similar to Denis Nardin's answe …
1
vote
rationalization of classifying spaces
This is a longish comment on James Schwass's answer, not an answer to the
original questions.
Have to be a little careful here. We are deliberately informal (p.97),
but we are working in a catego …
12
votes
Equivariant classifying spaces from classifying spaces
Charles, thanks for asking. This is not an answer, but it is too long for a comment. Like you, I encourage others to pursue the question and closely related ones I'll raise here. The paper of mine yo …
4
votes
Two commuting operad actions
Something very close to this and quite possibly relevant occurs in the theory of $E_{\infty}$ ring spaces. There is a notion of an action of an operad $Q$ on an operad $P$. When $Q$ acts on $P$, the …
3
votes
Classifying spaces of topological groups that are not well-pointed
I don't have a real answer but possibly relevant observations and speculations. I imagine $BG$ can be pretty horrible if $G$ is not well-pointed, unless of course one uses the fat realization, when I …
9
votes
Accepted
Can the set of iso classes of G-equivariant H-bundles be given by ordinary homotopy classes ...
That guy that keeps getting mentioned here never claimed it in general because he does not
believe it in general. Think about $G=U(n)$ and about equivariant $K$-theory. This
is very close to the At …
13
votes
Accepted
what does BG classify? i.e. what is a principal fibration?
In view of the references to my Memoir, Classifying spaces and fibrations,
in other answers, I guess I should answer too. The requested answer is
implicit but not quite explicit there. Fix a groupli …