# Séminaires : Séminaire d'Algèbre

 Equipe(s) : gr, Responsables : J. Alev, D. Hernandez, B. Keller, Th. Levasseur, et S. Morier-Genoud. Email des responsables : Jacques Alev , David Hernandez , Bernhard Keller , Thierry Levasseur , Sophie Morier-Genoud Salle : Zoom ou hybride selon les orateurs. Info sur https://researchseminars.org/seminar/paris-algebra-seminar Adresse : Zoom ou IHP Salle 01 Description Le séminaire est prévu en présence à l'IHP et à distance. Pour les liens et mots de passe, merci de contacter l'un des organisateurs ou de souscrire à la liste de diffusion https://listes.math.cnrs.fr/wws/info/paris-algebra-seminar. L'information nécessaire sera envoyée par courrier électronique peu avant chaque exposé. Les notes et transparents sont disponibles ici.   Since March 23, 2020, the seminar has been taking place remotely. For the links and passwords, please contact one of the organizers or subscribe to the mailing list at https://listes.math.cnrs.fr/wws/info/paris-algebra-seminar. The connexion information will be emailed shortly before each talk. Slides and notes are available here.

 Orateur(s) Amnon YEKUTIELI - Ben Gurion University, Israel et Université Paris 7, Titre Weak proregularity, weak stability and the noncommutative MGM equivalence Date 27/02/2017 Horaire 14:00 à 15:00 Diffusion Résume Let $A$ be a commutative ring, and let $\frak{a}$ be a finitely generated ideal in it. It is known that a necessary and sufficient condition for the derived $\frak{a}$-torsion and the derived $\frak{a}$-adic completion functors to be nicely behaved is the weak proregularity of the ideal $\frak{a}$. In particular, the MGM Equivalence holds under this condition. Because weak proregularity is defined in terms of elements of the ring (specifically, it involves limits of Koszul complexes), it is not suitable for noncommutative ring theory. Consider a torsion class $T$ in the category $M(A)$ of left modules over a ring $A$. We introduce a new condition on $T$: weak stability. Our first main theorem is that when $A$ is commutative, an ideal $\frak{a}$ in $A$ is weakly proregular if and only if the corresponding torsion class $T$ in $M(A)$ is weakly stable. It turns out that when the ring $A$ is noncommutative, one must impose two more conditions on the torsion class $T$: quasi-compactness and finite dimensionality (these are new names for old conditions). We prove that for a torsion class $T$ that is weakly stable, quasi-compact and finite dimensional, the right derived $T$-torsion functor is isomorphic to a left derived tensor functor. This result involves derived categories of bimodules. Some examples will be given. The third main theorem is the Noncommutative MGM Equivalence, under the same assumptions on $T$. Finally, there is a theorem about derived left-sided and right-sided torsion for complexes of bimodules. This last theorem is a generalization of a result of Van den Bergh from 1997, and it corrects an error in a paper of Yekutieli-Zhang from 2003. We expect that the approach outlined in this talk will open up the way to a useful theory of rigid dualizing complexes in the arithmetic noncommutative setting (namely without a base field). The work above is joint with Rishi Vyas. Salle Zoom ou hybride selon les orateurs. Info sur https://researchseminars.org/seminar/paris-algebra-seminar Adresse Zoom ou IHP Salle 01