# 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 : à distance / remote Adresse : IHP Description Depuis le 23 mars 2020, le séminaire se tient 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) Giovanni CERULLI - Bonn, Titre Degenerate flag varieties and quiver Grassmannians Date 12/12/2011 Horaire 14:30 à 15:30 Diffusion Résume In a recent paper in collaboration with E. Feigin and M. Reineke we investigate the connection beetween flag varieties and their degenerations, with quiver Grassmannians associated with representations of a Dynkin quiver. In previous works, E. Feigin introduced a natural degeneration of (partial) flag varieties. He showed that these varieties are (typically singular) irreducible, normal, local complete intersection which are flat degenerations of the usual flag varieties. Moreover they admit a group action with finitely many orbits and a cellular decomposition. The number of cells equals the (median) Genocchi numbers. In the paper we observed that these varieties are naturally isomorphic to quiver Grassmannians of the form $Gr_{\dim A}(A+A*)$, where $A$ is the path algebra of an equioriented quiver of type A. We hence consider quiver Grassmannians of the form $Gr_{\dim P} (P+I)$, where $P$ and $I$ are respectively a projective and an injective representation of a Dynkin quiver. We find the same properties as for type A. Moreover we compute the Poincaré polynomials of these varieties, finding a natural $q$-version of the median Genocchi numbers. Salle à distance / remote Adresse IHP