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Consider based maps $f : X \to Z$ and $g : Y \to Z$, which induces the following map at the based loop space level : $$\theta := \mu_Z \circ \big(\Omega f \times \Omega g) : \Omega(X\times Y) = \Omega X \times \Omega Y \to \Omega Z \times \Omega Z \to \Omega Z,$$ where $\mu_Z$ is the standard choice of loop concatenation. Suppose we are given that $\theta$ is an $A_2$ map in the sense that there is a homotopy $$\mu_Z \circ (\theta \times \theta) \simeq \theta \circ \mu_{X\times Y},$$ where $\mu_{X\times Y}$ is the standard concatenation in $\Omega(X\times Y)$.

Question: Can we claim that $\theta$ is an $A_\infty$-map? In particular, assuming suitable connectivity of $X,Y,Z$, can we deloop $\theta$ to get a map $X\times Y \to Z$?

I understand it is probably too much to ask for! But here is my approach. I will consider the interval operad $\mathcal{E}_1$ as the $A_\infty$-operad acting on the loop spaces. From this, I am able to prove that the following diagrams are homotopy commutative for each $n$ : $$\require{AMScd} \begin{CD} \mathcal{E}_1(n) \times \big(\Omega(X\times Y)\big)^n @>{}>> \Omega(X\times Y)\\ @V{1\times \theta^n}VV @VV{\theta}V\\ \mathcal{E}_1(n) \times \big(\Omega Z\big)^n @>>> \Omega Z \end{CD}$$

This is weaker than the notion of $\mathcal{E}_1$-map as in The Geometry of Iterated Loop Spaces by J. P. May, and so I am unable to apply the recognition principle directly. On the other hand, I have come across articles in the algebraic context (e.g., this one), where the author considers the above as the definition of an $E_\infty$-coalgebra map. Also, at the very end of the same monograph by May, the author notes that the theory can possibly be weaken to include homotopy morphisms. In the article Strong homotopy algebras over monads by T. Lada, the author introduced a notion of strong homotopy morphism, which asks for higher homotopy relations, and proved the recognition principle. But the $\theta$ map is not a strong homotopy morphism (in the sense of T. Lada) either. Can we still expect a recognition principle without higher homotopy relations?

Any comment or reference regarding this will be highly appreciated.

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1 Answer 1

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No, take $Z$ a connected space for which $\Omega Z$ is homotopy commutative but $Z$ has no $A_\infty$ multiplication, e.g. $Z$ could be an $H$-space which doesn't have the homotopy type of a loop space. If $f=g=\mathrm{Id}_Z$, then the multiplication $\Omega Z \times \Omega Z \rightarrow \Omega Z$ is an $A_2$-map by the hypothesis of homotopy commutativity and and Eckmann-Hilton argument. If it were an $A_\infty$ map, we could apply the bar construction to achieve a map $B(\Omega Z \times \Omega Z)=B\Omega Z \times B\Omega Z \rightarrow B \Omega Z$ which is an $A_\infty$ multiplication. Since $Z$ is connected $B\Omega Z \simeq Z$, so we have produced an $A_\infty$ multiplication on $Z$ which contradicts our assumption.

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  • $\begingroup$ Why is the bar construction producing an $A_\infty$-map? Also, note that I'm assuming that $\theta$ is an $A_2$ map. If I understand it correctly, the multiplication map on $\Omega Z$ is $A_2$ if and only if $\Omega Z$ is homotopy commutative. $\endgroup$
    – ChesterX
    Commented Jun 13, 2023 at 11:15
  • $\begingroup$ @ChesterX You are right, but you have actually added the information needed to correct the argument. Suppose $G$ is a homotopy commutative $A_\infty$ space which is not a double loop space (for example, the loop space of an $H$-space which is not $A_\infty$ should do). Then your observation shows the argument above can be applied to $BG$. I will edit the answer to correct the argument. $\endgroup$ Commented Jun 13, 2023 at 17:11
  • $\begingroup$ @ChesterX And the easiest reason to see why the bar construction produces an $A_\infty$ map is to just use the rectification theorem for $A_\infty$ monoids which means we can assume every multiplication is strictly associative. Then just apply bar constructions to the associativity of the multiplication $\Omega Z$. $\endgroup$ Commented Jun 13, 2023 at 18:36
  • $\begingroup$ I am still a bit confused about the $A_\infty$-multiplication part! If I understand your argument correctly, then you are saying that if $\mu_Z : \Omega Z \times \Omega Z \to \Omega Z$ is an $A_\infty$ map, then $Z$ is a loop space. In particular, $\Omega Z$ is actually an $E_2$-space. Am I correct? $\endgroup$
    – ChesterX
    Commented Jun 14, 2023 at 4:03
  • $\begingroup$ @ChesterX Yes, that's correct provided $Z$ is connected. $\endgroup$ Commented Jun 14, 2023 at 9:51

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