On a universal characterisation of $p$-typical Witt vectors

Abstract: For a prime $p$ and a commutative ring $R$ with unity, let $W(R)$ denote the ring of $p$-typical Witt vectors. The ring $W(R)$ is endowed with a Verschiebung operator $W(R)\xrightarrow{V}W(R)$ and a Teichm\"{u}ller map $R\xrightarrow{\langle \ \rangle}W(R)$. One of the properties satisfied by $V, \langle \ \rangle$ is that the map $R \to W(R)$ given by $x\mapsto V\langle x^p\rangle - p\langle x \rangle$ is an additive map. In this paper we show that for $p\neq 2$, this property essentially characterises the functor $W$. Unlike other characterisations, this only uses the group structure on $W(R)$ and hence is suitable for generalising to the non-commutative setup. We give a conjectural characterisation of Hesselholt's functor of $p$-typical Witt vectors using a universal property for $p\neq 2$. Moreover we provide evidence for this conjecture.