English

A universal group-theoretic characterisation of $p$-typical Witt vectors

Number Theory 2026-01-29 v2 Rings and Algebras

Abstract

For a prime pp and a commutative ring RR with unity, let W(R)W(R) denote the group of pp-typical Witt vectors. The group W(R)W(R) is endowed with a Verschiebung operator V:W(R)W(R)V: W(R)\to W(R) and a Teichm\"{u}ller map  :RW(R)\langle \ \rangle: R\rightarrow W(R). One of the properties satisfied by V, V, \langle \ \rangle is that the map RW(R)R \to W(R) given by xVxppxx\mapsto V\langle x^p \rangle - p\langle x \rangle is an additive map. In this paper we show that for p2p\neq 2, this property essentially characterises the functor WW. Unlike other characterisations, this is a group-theoretic characterisation, in the sense that it does not use the ring structure of W(R)W(R). Most constructions of the group of pp-typical Witt vectors of non-commutative rings do not have a ring structure, and hence the above characterisation is more suitable for generalisation to the non-commutative setup.

Keywords

Cite

@article{arxiv.2405.12680,
  title  = {A universal group-theoretic characterisation of $p$-typical Witt vectors},
  author = {Supriya Pisolkar and Biswanath Samanta},
  journal= {arXiv preprint arXiv:2405.12680},
  year   = {2026}
}

Comments

Revised version(8 pages). The non-commutative part of the previous version has been removed due to an error