Conjectural computation of topological Hochschild homology of truncated Brown–Peterson spectra

Let BnB\langle n\rangle be an E3E_3 form of BPnBP\langle n\rangle. For 1mn1\leq m\leq n and n1n\geq 1, write P()P(-) for a polynomial algebra and E()E(-) for an exterior algebra. Define

Tmn=P(vm)E(λ1,,λnm){as,(k):≢p1(modp),s1}/,T_m^n=P(v_m)\otimes E(\lambda_1,\dots,\lambda_{n-m})\{a_{s,\ell}^{(\underline{k})}:\ell\not\equiv p-1\pmod p,s\geq 1\}/\simeq,

where k=(ϵ1,,ϵm)\underline{k}=(\epsilon_1,\dots,\epsilon_m) with each ϵi{0,1}\epsilon_i\in\{0,1\}, and where \simeq is generated by

vmrn(s,m)λ1ϵ1λnmϵnmas,(k)0.v_m^{r_n(s,m)}\lambda_1^{\epsilon'_1}\cdots\lambda_{n-m}^{\epsilon'_{n-m}}a_{s,\ell}^{(\underline{k})}\sim 0.

Here

rn(s,m)=pnm+s+pnm+s(m+1)++pn+jm,r_n(s,m)=p^{n-m+s}+p^{n-m+s-(m+1)}+\cdots+p^{n+j-m},

with j{1,,m+1}j\in\{1,\dots,m+1\} uniquely determined by sj(modm+1)s\equiv j\pmod{m+1}, and the classes λs\lambda_s are recursively defined by

λs:={λs1sn+1,λs(m+1)μn+1ps(n+2)(p1)s>n+1.\lambda_s:=\begin{cases}\lambda_s&1\leq s\leq n+1,\lambda_{s-(m+1)}\mu_{n+1}^{p^{s-(n+2)}(p-1)}&s>n+1.\end{cases}

The element as,(k)a_{s,\ell}^{(\underline{k})} projects to

λnm+sλnm+s+1ϵ1λn+sϵmμn+1ps1E,0.\lambda_{n-m+s}\lambda_{n-m+s+1}^{\epsilon_1}\cdots\lambda_{n+s}^{\epsilon_m}\mu_{n+1}^{\ell p^{s-1}}\in E_\infty^{*,0}.

Conjectural THH computation. There is an isomorphism

THH(Bn;k(m))P(vm)E(λ1,,λnm)Tmn.\operatorname{THH}_*(B\langle n\rangle;k(m))\cong P(v_m)\otimes E(\lambda_1,\dots,\lambda_{n-m})\oplus T_m^n.

This proposes a uniform description of the topological Hochschild homology of truncated Brown–Peterson spectra with coefficients in k(m)k(m), extending the calculations preceding it; the supplied text does not state a resolution or provide evidence that settles the conjecture.

Sources & referencesView supporting material

Primary source

Gabriel Angelini-Knoll, Dominic Leon Culver and Eva Höning, “Topological Hochschild homology of truncated Brown-Peterson spectra I”, arXiv:2106.06785 (2023).

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