Skip to main content
1 of 2
Emily
  • 11.8k
  • 4
  • 30
  • 88

$(-n-1)$-connected spectra vs. reduced excisive functors from $n$-truncated pointed spaces

It's possible to view nonconnectivity for spectra as arising from enlarging Segal's category $\Gamma^\mathsf{op}\overset{\mathrm{def}}{=}\mathsf{Sk}(\mathrm{FinSets}_*)$ to the $\infty$-category of finite pointed spaces $\mathcal{S}^\mathrm{fin}_*$, see Dmitri's answer here.

I'm interested on whether the following refinement of this statement is true:

We have an equivalence of $\infty$-categories $$\mathsf{Exc}_*(\mathcal{S}^{\mathrm{fin}}_{\leq n,*},\mathcal{S})\overset{\mathrm{eq.}}{\cong}\mathsf{Sp}_{\leq-n-1},$$ where

  • $\mathsf{Exc}_*(\mathcal{S}^{\mathrm{fin}}_{\leq n,*},\mathcal{S})$ is the $\infty$-category of reduced excisive functors from the $\infty$-category $\mathcal{S}^{\mathrm{fin}}_{\leq n,*}$ of finite $n$-truncated pointed spaces;
  • $\mathsf{Sp}_{\leq-n-1}$ is the $\infty$-category of $(-n-1)$-connected spectra.

The $n=0$ case of the above statement is true; again, see Dmitri's answer.


Additionally, we have a fully faithful inclusion of $\infty$-categories $\iota\colon\mathcal{S}^{\mathrm{fin}}_{\leq n,*}\hookrightarrow\mathcal{S}^{\mathrm{fin}}_{*}$, giving functors \begin{align*} \iota^* &\colon \mathsf{Sp}\to\mathsf{Exc}_*(\mathcal{S}^{\mathrm{fin}}_{\leq n,*},\mathcal{S}),\\ \mathrm{Lan}_{\iota} &\colon \mathsf{Exc}_*(\mathcal{S}^{\mathrm{fin}}_{\leq n,*},\mathcal{S})\to\mathsf{Sp},\\ \mathrm{Ran}_{\iota} &\colon \mathsf{Exc}_*(\mathcal{S}^{\mathrm{fin}}_{\leq n,*},\mathcal{S})\to\mathsf{Sp}. \end{align*} If we indeed have $\mathsf{Exc}_*(\mathcal{S}^{\mathrm{fin}}_{\leq n,*},\mathcal{S})\overset{\mathrm{eq.}}{\cong}\mathsf{Sp}_{\leq-n-1}$ as above, it would be natural to wonder if $\iota^*$ is just $(-n-1)$-truncation of spectra. If the above quoted statement is true, is $\iota^*$ indeed given by $(-n-1)$-truncation? What about $\mathrm{Lan}_{\iota}$ and $\mathrm{Ran}_{\iota}$?

Emily
  • 11.8k
  • 4
  • 30
  • 88