English

Algebraization of Mochizuki's anabelian variation of ring structures, perfectoid geometry and formal groups

Algebraic Geometry 2024-10-14 v6 Number Theory

Abstract

Let MM be a multiplicative monoid with identity. Then I show that there is a universal one dimensional formal group law equipped with an action of MM. If MM is pp-perfect (i.e. mmpm\mapsto m^p is an isomorphism for some prime number pp) then the universal MM-formal group law comes equipped with a natural Frobenius endomorphism. There are a number of concrete applications of this result. If KK is a pp-adic field and O=OK\mathcal{O}=\mathcal{O}_K is the multiplicative monoid of the ring of integers of KK, then there is a universal formal group (over a suitable (non-zero) ring) which is equipped with an action of the multiplicative monoid O\mathcal{O}. Lubin-Tate formal groups arise from this universal monoid formal group law. This has applications to Mochizuki's anabelian ideas: if two p-adic fields have isomorphic absolute Galois groups then they have isomorphic multiplicative monoids O\mathcal{O} (but possibly non-isomorphic ring structures). The existence of the universal monoid formal group law for the monoid O\mathcal{O} implies that the additive structures of a ring can be interpolated into a universal algebraic family (while keeping the multiplicative structure of the ring fixed). Here is another important example covered by my result: let RR be a perfectoid ring and let RR^\flat be its tilt and the multiplicative monoid RR^\flat of RR^\flat. Then there exists a universal monoid formal group law for this monoid which interpolates the additive structures of untilts with tilt RR^\flat. Thus in some sense one has a unified approach to various phenomenon which are well-known in anabelian geometry and in perfectoid geometry. These results also provide a natural number field version of Fontaine's fundamental ring AinfA_{inf} of pp-adic Hodge Theory (Section 4.3).

Keywords

Cite

@article{arxiv.1906.06840,
  title  = {Algebraization of Mochizuki's anabelian variation of ring structures, perfectoid geometry and formal groups},
  author = {Kirti Joshi},
  journal= {arXiv preprint arXiv:1906.06840},
  year   = {2024}
}

Comments

23 Pages. Replaced Remark 4.2.4 by Section 4.3. From previous vers.: Added Remark 4.2.4--Completely revised version. Title slightly changed