Excellent metrics on triangulated categories, and the involutivity of the map taking $\mathcal{S}$ to $\mathfrak{S}({\mathcal{S})^{\mathrm{op}}}$ (2505.09120v1)

Abstract: In the article arXiv:1806.06471 we defined good metrics on triangulated categories, and then studied the construction, that began with a triangulated category $\mathcal{S}$ together with a good metric ${\mathcal{M}_i,\,i\in\mathbb{N}}$, and out of it cooked up another triangulated category $\mathfrak(\mathcal{S})$. We went on to study examples, and produced many for which the construction is involutive. By this we mean that, if you let $\mathcal{T}=\mathfrak{S}(\mathcal{S})^{\mathrm{op}}$, then there is a choice of metric on $\mathcal{T}$ for which $\mathcal{S}=\mathfrak{S}(\mathcal{T})^{\mathrm{op}}$. In this article we study this phenomenon much more carefully, with the focus being on understanding the metrics for which involutivity occurs. As it turns out there is a large class of them, the excellent metrics on triangulated categories. At the end we will produce a few new examples of excellent metrics. And our reason for going to all this trouble is that the results of this article will permit us to prove new and surprising statements about uniqueness of enhancements. Those results will come in a sequel to this article, which is joint with Canonaco and Stellari.