Fiberwise building and stratification in tensor triangular geometry

Abstract: We give conditions on a family of coproduct-preserving tt-functors $f_i\colon \mathcal{T}\to \mathcal{T}_i$ between tt-categories with small coproducts, ensuring that the localizing tensor-ideal generated by an object $x$ in $\mathcal{T}$ is built from those objects whose image under $f_i$ lies in the localizing tensor-ideal generated by $f_i(x)$ for all $i$. This allows us to provide a criterion for stratification on a fiberwise level when restricted to big tt-categories. As an application, we show that the big derived category of permutation modules for a finite group over an arbitrary Noetherian base is indeed stratified. Furthermore, our approach extends to the category of representations of a finite group scheme over a Noetherian base, thereby recovering a recent result from the literature.