{"id":325,"date":"2025-11-05T09:22:44","date_gmt":"2025-11-05T08:22:44","guid":{"rendered":"https:\/\/www.imj-prg.fr\/tga\/?p=325"},"modified":"2025-11-24T13:37:01","modified_gmt":"2025-11-24T12:37:01","slug":"demi-journee-dequipe-25-novembre-2025","status":"publish","type":"post","link":"https:\/\/www.imj-prg.fr\/tga\/demi-journee-dequipe-25-novembre-2025\/","title":{"rendered":"Demi-journ\u00e9e d\u2019\u00e9quipe \u2013 25 novembre 2025"},"content":{"rendered":"\n<p>La prochaine (demi-)journ\u00e9e de l&rsquo;\u00e9quipe TGA aura lieu le mardi 25 novembre 2025, de 14h \u00e0 18h \u00e0 Sophie Germain (salle 1016). Nous aurons le plaisir d&rsquo;\u00e9couter :<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>(14h-14h30) <strong>Alessandro Chiodo<\/strong> : <em>Le lieu des fibr\u00e9s en droites triviaux<\/em><br>Sur une famille de courbes lisses C au-dessus d&rsquo;une base S, on consid\u00e8re un fibr\u00e9 en droite L et on \u00e9tudie le lieu des points p de S o\u00f9 le fibr\u00e9 L_p est trivial sur la courbe C_p. Quand la famille C\/S est lisse, ou m\u00eame nodale mais irr\u00e9ductible, on peut d\u00e9finir et calculer ais\u00e9ment un cycle alg\u00e9brique support\u00e9 sur ce lieu \u00e0 l&rsquo;aide des classes de Chern via la formule de Thom-Porteous. Quand cette \u00e9tude est \u00e9tendue \u00e0 une famille de courbes stables, on peut encore d\u00e9finir un cycle alg\u00e9brique, mais la m\u00e9thode pr\u00e9c\u00e9dente \u00e9choue. Avec David Holmes on d\u00e9crit plusieurs fa\u00e7ons de d\u00e9terminer ce cycle et ses variantes.<\/li>\n\n\n\n<li>(14h45-15h15) <strong>Cyril Demarche<\/strong> : <em>Rel\u00e8vement de repr\u00e9sentations de certains groupes de Galois et de certains groupes fondamentaux<\/em><br>Dans un travail en commun avec Andrea Conti et Mathieu Florence, nous \u00e9tudions les repr\u00e9sentations de groupes profinis satisfaisant une dualit\u00e9 de Poincar\u00e9 de dimension 2, dont les groupes de Galois absolus de corps locaux et les (compl\u00e9tions de) groupes fondamentaux de surfaces compactes orientables sont deux exemples. Nous montrons en particulier que, sous une hypoth\u00e8se sur les racines de l&rsquo;unit\u00e9 dans le cas arithm\u00e9tique, toute repr\u00e9sentation modulo p d&rsquo;un tel groupe se rel\u00e8ve en une repr\u00e9sentation modulo p^2, et que toute repr\u00e9sentation unipotente modulo p se rel\u00e8ve modulo p^r, pour tout r. L&rsquo;approche et la preuve se veulent les plus \u00e9l\u00e9mentaires possibles, et reposent sur la th\u00e9orie de Kummer et la dualit\u00e9 de Poincar\u00e9.<\/li>\n\n\n\n<li>(15h45-16h15) <strong>Danica Kosanovi\u0107<\/strong> : <em>Diffeomorphisms from dancing circles<\/em><br>It is still unknown whether every diffeomorphism of the 4-sphere is isotopic to the identity, i.e. whether the smooth mapping class group is trivial or not. I will explain how all candidate classes constructed recently arise from 1-parameter families of embedded circles, and often reduce to a single class. Analogues of such classes have been shown to be nontrivial in some non-simply connected 4-manifolds.<\/li>\n\n\n\n<li>(16h30-17h) <strong>\u00c1ngel David R\u00edos Ortiz<\/strong> : <em>Coble duality for Hyperk\u00e4hler Kummer fourfolds<\/em><br>Hyperk\u00e4hler manifolds have recently gained attention for their rich and fascinating geometry. The deformation theory of Hyperk\u00e4hler manifolds allows to group polarized hyper-Kahler manifolds &#8211; the pair of one such variety and an ample line bundle &#8211; in moduli spaces.<br>The challenge of understanding the geometry of a general element of such spaces is naturally related to whether the moduli spaces admit nice parametrizations, in particular if they are unirational.<br>I will present a joint work with Daniele Agostini, Pietro Beri and Franco Giovenzana, which represents a first step in the understanding of such questions. In this project, we focus on a family of hyper-Kahler manifolds called generalised Kummer fourfolds. We discover even more structure that comes from projective duality between two a priori unrelated projective spaces.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>La prochaine (demi-)journ\u00e9e de l&rsquo;\u00e9quipe TGA aura lieu le mardi 25 novembre 2025, de 14h \u00e0 18h \u00e0 Sophie Germain (salle 1016). Nous aurons le plaisir d&rsquo;\u00e9couter :<\/p>\n","protected":false},"author":41,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-325","post","type-post","status-publish","format-standard","hentry","category-non-classe"],"_links":{"self":[{"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/posts\/325","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/users\/41"}],"replies":[{"embeddable":true,"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/comments?post=325"}],"version-history":[{"count":7,"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/posts\/325\/revisions"}],"predecessor-version":[{"id":333,"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/posts\/325\/revisions\/333"}],"wp:attachment":[{"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/media?parent=325"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/categories?post=325"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.imj-prg.fr\/tga\/wp-json\/wp\/v2\/tags?post=325"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}