Published online by Cambridge University Press: 24 May 2016
In this paper we demonstrate that non-commutative localizations of arbitrary additive categories (generalizing those defined by Cohn in the setting of rings) are closely (and naturally) related to weight structures. Localizing an arbitrary triangulated category $\text{}\underline{C}$ by a set
$S$ of morphisms in the heart
$\text{}\underline{Hw}$ of a weight structure
$w$ on it one obtains a triangulated category endowed with a weight structure
$w^{\prime }$. The heart of
$w^{\prime }$ is a certain version of the Karoubi envelope of the non-commutative localization
$\text{}\underline{Hw}[S^{-1}]_{\mathit{add}}$ (of
$\text{}\underline{Hw}$ by
$S$). The functor
$\text{}\underline{Hw}\rightarrow \text{}\underline{Hw}[S^{-1}]_{\mathit{add}}$ is the natural categorical version of Cohn’s localization of a ring, i.e., it is universal among additive functors that make all elements of
$S$ invertible. For any additive category
$\text{}\underline{A}$, taking
$\text{}\underline{C}=K^{b}(\text{}\underline{A})$ we obtain a very efficient tool for computing
$\text{}\underline{A}[S^{-1}]_{\mathit{add}}$; using it, we generalize the calculations of Gerasimov and Malcolmson (made for rings only). We also prove that
$\text{}\underline{A}[S^{-1}]_{\mathit{add}}$ coincides with the ‘abstract’ localization
$\text{}\underline{A}[S^{-1}]$ (as constructed by Gabriel and Zisman) if
$S$ contains all identity morphisms of
$\text{}\underline{A}$ and is closed with respect to direct sums. We apply our results to certain categories of birational motives
$DM_{gm}^{o}(U)$ (generalizing those defined by Kahn and Sujatha). We define
$DM_{gm}^{o}(U)$ for an arbitrary
$U$ as a certain localization of
$K^{b}(Cor(U))$ and obtain a weight structure for it. When
$U$ is the spectrum of a perfect field, the weight structure obtained this way is compatible with the corresponding Chow and Gersten weight structures defined by the first author in previous papers. For a general
$U$ the result is completely new. The existence of the corresponding adjacent
$t$-structure is also a new result over a general base scheme; its heart is a certain category of birational sheaves with transfers over
$U$.
Theorem 0.1 and Theorem 4.2.3 were proven under support of the Russian Science Foundation grant no. 14-21-00035. The research was also supported by RFBR grant no. 15-01-03034-a. Besides, the first author was supported by RFBR (grants no. 14-01-00393-a) and by Dmitry Zimin’s Foundation ‘Dynasty’; the second author was supported by the Chebyshev Laboratory (Department of Mathematics and Mechanics, St. Petersburg State University), by JSC ‘Gazprom Neft’, and by the Saint-Petersburg State University research grant no. 38.37.208.2016.