Examples of disk algebras

Abstract

We produce refinements of the known multiplicative structures on the Brown--Peterson spectrum $BP$, its truncated variants $BP⟨n⟩$, Ravenel's spectra $X(n)$, and evenly graded polynomial rings over the sphere spectrum. Consequently, topological Hochschild homology relative to these rings inherits a circle action.

v2: Fixed erroneous sentence in the introduction. 8 pages. Comments always welcome