BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Sachi Hashimoto (Boston University) DTSTART:20200527T190000Z DTEND:20200527T200000Z DTSTAMP:20260404T094802Z UID:etag2020/1 DESCRIPTION:Title: An obstruction to weak approximation on a Calabi-Yau threefold \nby Sachi Hashimoto (Boston University) as part of Experimental Talks in Algebraic Geometry\n\n\nAbstract\nIn this talk\, we investigate the arithm etic structure of a class of Calabi-Yau threefolds. These threefolds were constructed over the complex numbers by Hosono and Takagi as a linear sect ion of a double quintic symmetroid\, and have a beautiful and simple story in the geometry of quadrics over the rational numbers. In forthcoming wor k with Honigs\, Lamarche\, and Vogt\, we exhibit an obstruction to weak ap proximation on these threefolds. For the "experimental" nature of this sem inar\, we will conclude by working through a demonstration in cocalc. Atte ndees are asked to make cocalc accounts to participate fully\; no prior co ding experience necessary!\n LOCATION:https://stable.researchseminars.org/talk/etag2020/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Soumya Sankar (University of Wisconsin\, Madison) DTSTART:20200603T190000Z DTEND:20200603T200000Z DTSTAMP:20260404T094802Z UID:etag2020/2 DESCRIPTION:Title: Counting elliptic curves with a rational N-isogeny\nby Soumya Sankar (University of Wisconsin\, Madison) as part of Experimental Talks i n Algebraic Geometry\n\n\nAbstract\nThe problem of counting elliptic curve s over Q with a rational N isogeny can be rephrased as a question of count ing rational points on the moduli stacks X_0(N). In this talk\, I will dis cuss heights on projective varieties and a generalization to stacks of cer tain kinds\, based on upcoming work of Ellenberg\, Satriano and Zureick-Br own. We will then use this to count points on X_0(N) for low N. This is j oint work with Brandon Boggess.\n LOCATION:https://stable.researchseminars.org/talk/etag2020/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Kristin DeVleming (University of California\, San Diego) DTSTART:20200617T190000Z DTEND:20200617T200000Z DTSTAMP:20260404T094802Z UID:etag2020/4 DESCRIPTION:Title: Moduli spaces of plane curves\nby Kristin DeVleming (Universit y of California\, San Diego) as part of Experimental Talks in Algebraic Ge ometry\n\n\nAbstract\nCompactifying moduli spaces has been a fundamental p roblem in algebraic geometry that has been richly developed in the past 50 years. In that time\, many different perspectives have been studied and t hese have resulted in many different compactifications. Starting from an a udience discussion\, we will consider the moduli space of plane curves of fixed degree\, some potential compactifications\, and how they fit togethe r. Based on that discussion\, I will mention a few of my favorite proper m oduli spaces of plane curves\, discuss their relationships\, and pose some open questions.\n LOCATION:https://stable.researchseminars.org/talk/etag2020/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Andrew Kobin (University of California\, Santa Cruz) DTSTART:20200701T190000Z DTEND:20200701T200000Z DTSTAMP:20260404T094802Z UID:etag2020/5 DESCRIPTION:Title: Zeta functions in number theory\, algebraic geometry and beyond\nby Andrew Kobin (University of California\, Santa Cruz) as part of Expe rimental Talks in Algebraic Geometry\n\n\nAbstract\nParticipants will have a chance to fondly recall their favourite zeta functions. Together\, we w ill discuss how different examples relate to/generalize each other. Then I will describe a general framework for studying zeta functions using decom position spaces from homotopy theory.\n LOCATION:https://stable.researchseminars.org/talk/etag2020/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Takumi Murayama (Princeton University) DTSTART:20200624T190000Z DTEND:20200624T200000Z DTSTAMP:20260404T094802Z UID:etag2020/6 DESCRIPTION:Title: Every variety is birational to a weakly normal hypersurface\nb y Takumi Murayama (Princeton University) as part of Experimental Talks in Algebraic Geometry\n\n\nAbstract\nClassically\, it is known that every var iety is birational to a projective hypersurface. For curves and surfaces\, this hypersurface can be taken to have at worst nodal and at worst ordina ry singularities\, respectively. We will prove that in arbitrary dimension \, this hypersurface can be taken to be weakly normal\, and for smooth pro jective varieties of dimension at most five\, this hypersurface can be tak en to have semi-log canonical singularities. These results are due to Robe rts and Zaare-Nahandi and to Doherty in characteristic zero\, respectively \, and to Rankeya Datta and myself in positive characteristic. Attendees w ill be asked to do some concrete computations with polynomials.\n LOCATION:https://stable.researchseminars.org/talk/etag2020/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Madeline Brandt (University of California\, Berkeley) DTSTART:20200708T190000Z DTEND:20200708T200000Z DTSTAMP:20260404T094802Z UID:etag2020/8 DESCRIPTION:Title: Limits of Voronoi and Delaunay Cells\nby Madeline Brandt (Univ ersity of California\, Berkeley) as part of Experimental Talks in Algebrai c Geometry\n\n\nAbstract\nVoronoi diagrams of finite point sets partition space into regions. Each region contains all points which are\nnearest to one point in the finite point set. Voronoi diagrams (and their generalizat ions and variations)\nhave been an object of interest for hundreds of year s by mathematicians spanning many fields\, and they\nhave numerous applica tions across the sciences. Recently\, Cifuentes\, Ranestad\, Sturmfels\, a nd Weinstein\ndefined Voronoi cells of varieties\, in which the finite poi nt set is replaced by a real algebraic variety. Each\npoint y on the varie ty has a cell of points in the ambient space corresponding to those points which are\ncloser to y than any other point on the variety. In this talk\ , we present the limiting behavior of Voronoi\ndiagrams of finite sets\, w here the finite sets are sampled from the variety and the sample size incr eases. In\nthis setting\, we observe that many interesting features of the variety can be seen in a Voronoi Diagram\,\nincluding its medial axis\, c urvatures\, normals\, reach\, and singularities.\n LOCATION:https://stable.researchseminars.org/talk/etag2020/8/ END:VEVENT END:VCALENDAR