$q$-crystals and $q$-connections

Abstract

We study how the category of $q$-connections depends on the choice of coordinates. We exploit Bhatt's and Scholze's $q$-crystalline site, which is based on a coordinate free formulation of $q$-PD structures, in order to relate $q$-crystals and $q$-connections in the $p$-adic setting. This yields a natural equivalence between the the categories of $q$-connections for different choices of coordinates in the $p$-adic setting. The equivalence can be described explicitly in terms of differential operators. In order to obtain a global equivalence, we patch the $p$-adic differential operators to create a global one. The process is not entirely formal, and we are only able to obtain a global equivalence after inverting $2$.