# Modular Model Categories

## TL;DR

This paper introduces a new framework for associating modular model categories to small categories, especially schemes, enabling parametrization of model categories by various small categories, with applications to algebraic geometry.

## Contribution

It defines a functorial construction of modular model categories parametrized by small categories, including schemes, and explores their applications in algebraic geometry and homotopy theory.

## Key findings

- Constructs a functor $ ext{ModCat} o ext{Cat}$ associating modular model categories to small categories.
- Provides a parametrization of model categories using schemes and compares different parametrizations.
- Lays groundwork for applying modular model categories to algebraic geometry contexts.

## Abstract

To any model category $\mathcal{M}$, we associate a modular model category, a functor of points $\mathcal{M}[-]:$ Cat $\rightarrow$ Cat, that associates to any small category $\mathcal{C}$ a functor category $\mathcal{M}[\mathcal{C}] = \text{Fun}_{fes}(\mathcal{C}, \mathcal{M})$ of full and essentially surjective functors from $\mathcal{C}$ to $\mathcal{M}$, providing parametrizations of a same model category $\mathcal{M}$ by different small categories. We are in particular interested in using schemes as parameters. We consider $\mathbb{Z}$Sm$/k$ the category of linear combinations of smooth separated schemes of finite type over Spec($k$), $k$ a field, referred to as $\mathbb{Z}$-schemes, and let $\mathcal{C} = Sh(\mathbb{Z} \text{Sm}/k, \text{Nis})$. We contrast this with using the $\mathbb{A}^1$-homotopy category of $\mathbb{Z}$-schemes as a parametrizing category.