A Top-Down Approach to Algebraic Renormalization in Regularity Structures Based on Multi-indices

We provide an algebraic framework to describe renormalization in regularity structures based on multi-indices for a large class of semi-linear stochastic PDEs. This framework is “top-down”, in the sense that we postulate the form of the counterterm and use the renormalized equation to build a canonical smooth model for it. The core of the construction is a generalization of the Hopf algebra of derivations in Linares et al. (Commun Am Math Soc 3:1–64, 2023, https://doi.org/10.1090/cams/16), which is extended beyond the structure group to describe the model equation via an exponential map; this allow us to implement a renormalization procedure which resembles the preparation map approach in our context.