{ "149981-21907760": { "datetime_modified":"20261019T150024", "datetime_start":"20261023T150000", "datetime_end":"20261023T160000", "has_end_time":1, "date_start":"2026-10-23", "date_end":"2026-10-23", "time_start":"15:00:00", "time_end":"16:00:00", "time_zone":"America\/Detroit", "event_title":"Unexpected torus action on toric Richardson varieties", "occurrence_title":"", "combined_title":"Unexpected torus action on toric Richardson varieties: Soyeon Kim (UC Davis)", "event_subtitle":"Soyeon Kim (UC Davis)", "event_type":"Workshop \/ Seminar", "event_type_id":"21", "description":"This talk focuses on Richardson varieties in the complete flag variety, which are intersections of a Schubert variety with an opposite Schubert variety. Richardson varieties are indexed by intervals in the Bruhat order on the symmetric group. In joint work with E. Gorsky and M. Sherman-Bennett, we study the following question: when is a Richardson variety a toric variety? All Richardson varieties admit an action by an (n-1)- dimensional torus in SL_n, called the standard torus, which also acts on the complete flag variety. The Richardson varieties which are toric varieties with respect to the standard torus were classified independently by Anderson and Tsukerman--Williams. We found that there are many additional toric Richardson varieties, which we call \"unexpected\u201d. In this rather expository talk, I will classify toric Richardson varieties using the combinatorics of Bruhat intervals and focus on describing this \"unexpected\" torus action using the Marsh--Rietsch parametrization on open Richardson varieties. If time permits, I will mention my ongoing research in this direction.", "occurrence_notes":null, "guid":"149981-21907760@events.umich.edu", "permalink":"http:\/\/events.umich.edu\/event\/149981", "building_id":"1000166", "building_name":"East Hall", "campus_maps_id":"53", "room":"4088", "location_name":"East Hall", "has_livestream":0, "cost":"", "tags":["Mathematics"], "website":"", "sponsors":[ { "group_name":"Combinatorics Seminar - Department of Mathematics", "group_id":"4885", "website":"" } ], "image_url":"", "styled_images":{ "event_thumb":"", "event_large":"", "event_large_2x":"", "event_large_lightbox":"", "group_thumb":"", "group_thumb_square":"", "group_large":"", "group_large_lightbox":"", "event_large_crop":"", "event_list":"", "event_list_2x":"", "event_grid":"", "event_grid_2x":"", "event_feature_large":"", "event_feature_thumb":"" }, "occurrence_count":1, "first_occurrence":21907760 } , "149993-21907789": { "datetime_modified":"20261019T152959", "datetime_start":"20261030T150000", "datetime_end":"20261030T160000", "has_end_time":1, "date_start":"2026-10-30", "date_end":"2026-10-30", "time_start":"15:00:00", "time_end":"16:00:00", "time_zone":"America\/Detroit", "event_title":"Zamolodchikov Periodic Cluster Algebras", "occurrence_title":"", "combined_title":"Zamolodchikov Periodic Cluster Algebras: Ariana Chin (UCLA)", "event_subtitle":"Ariana Chin (UCLA)", "event_type":"Workshop \/ Seminar", "event_type_id":"21", "description":"In 2007, Fomin and Zelevinsky introduced the bipartite belt, a sequence of bipartite cluster mutations whose exchange relations form a discrete dynamical system. When the system is periodic, we call this Zamolodchikov periodicity. In this talk, we discuss the classification of all Zamolodchikov periodic cluster algebras, with connections to W-graphs, root systems, and maximal green sequences. We observe that there is a natural red-blue statistic on the associated tropical dynamics that is homomesic, and use laminations to prove it for finite type. This gives a natural bijection between colored mutations in the dynamical system and roots in the associated root system.", "occurrence_notes":null, "guid":"149993-21907789@events.umich.edu", "permalink":"http:\/\/events.umich.edu\/event\/149993", "building_id":"1000166", "building_name":"East Hall", "campus_maps_id":"53", "room":"4088", "location_name":"East Hall", "has_livestream":0, "cost":"", "tags":["Mathematics"], "website":"", "sponsors":[ { "group_name":"Combinatorics Seminar - Department of Mathematics", "group_id":"4885", "website":"" } ], "image_url":"", "styled_images":{ "event_thumb":"", "event_large":"", "event_large_2x":"", "event_large_lightbox":"", "group_thumb":"", "group_thumb_square":"", "group_large":"", "group_large_lightbox":"", "event_large_crop":"", "event_list":"", "event_list_2x":"", "event_grid":"", "event_grid_2x":"", "event_feature_large":"", "event_feature_thumb":"" }, "occurrence_count":1, "first_occurrence":21907789 } , "150159-21908304": { "datetime_modified":"20260812T081935", "datetime_start":"20261106T150000", "datetime_end":"20261106T160000", "has_end_time":1, "date_start":"2026-11-06", "date_end":"2026-11-06", "time_start":"15:00:00", "time_end":"16:00:00", "time_zone":"America\/Detroit", "event_title":"Combinatorics Seminar", "occurrence_title":"", "combined_title":"Combinatorics Seminar: Allen Knutson (Cornell University)", "event_subtitle":"Allen Knutson (Cornell University)", "event_type":"Workshop \/ Seminar", "event_type_id":"21", "description":"TBD", "occurrence_notes":null, "guid":"150159-21908304@events.umich.edu", "permalink":"http:\/\/events.umich.edu\/event\/150159", "building_id":"1000166", "building_name":"East Hall", "campus_maps_id":"53", "room":"4088", "location_name":"East Hall", "has_livestream":0, "cost":"", "tags":["Mathematics"], "website":"", "sponsors":[ { "group_name":"Combinatorics Seminar - 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