DGAs with polynomial homology

Abstract

In this work, we study the classification of differential graded algebras over $\mathbb{Z}$ (DGAs) whose homology is $\mathbb{F}_p[x]$, i.e. the polynomial algebra over $\mathbb{F}_p$ on a single generator. This classification problem was left open in work of Dwyer, Greenlees and Iyengar. For $\lvert y_{2p-2} \rvert = 2p-2$, we show that there is a unique non-formal DGA with homology $\mathbb{F}_p[y_{2p-2}]$ and a non-formal $2p-2$ Postnikov section. Among a classification result, this provides the first example of a non-formal DGA with homology $\mathbb{F}_p[x]$. By duality, this also shows that there is a non-formal DGA whose homology is an exterior algebra over $\mathbb{F}_p$ with a generator in degree $-(2p-1)$. Considering the classification of the ring spectra corresponding to these DGAs, we show that every $E_2$ DGA with homology $\mathbb{F}_p[x]$ (with no restrictions on $\lvert x \rvert$) is topologically equivalent to the formal DGA with homology $\mathbb{F}_p[x]$, i.e. they are topologically formal. This follows by a theorem of Hopkins and Mahowald.