BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Olivier Glorieux (IHES) DTSTART:20200519T140000Z DTEND:20200519T150000Z DTSTAMP:20260422T225704Z UID:Geometry/1 DESCRIPTION:Title: Critical exponents in higher rank symmetric spaces\nby Olivier Glorie ux (IHES) as part of Pangolin seminar\n\n\nAbstract\nThe aim of the talk i s to present some recent results on critical exponents for discrete subgro ups of higher rank semisimple Lie groups. We will survey classical results in negative curvature\, the relationship with entropy and the Hausdorff d imension of limit sets. Then we will introduce the geometric properties of higher rank symmetric spaces and explain the main differences with strict negative curvature. We will focus on two different results : the behaviou r of the critical exponent under normal subgroup (j.w. S. Tapie) and the e xtension of classical results to pseudo-riemannian geometry (j.w. D. Moncl air).\n LOCATION:https://researchseminars.org/talk/Geometry/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Roman Prosanov (Technische Universität Wien) DTSTART:20200602T140000Z DTEND:20200602T150000Z DTSTAMP:20260422T225704Z UID:Geometry/2 DESCRIPTION:Title: Rigidity of compact Fuchsian manifolds with convex boundary\nby Roman Prosanov (Technische Universität Wien) as part of Pangolin seminar\n\n\n Abstract\nBy a compact Fuchsian manifold with boundary we mean a hyperboli c 3-manifold homeomorphic to $S_g \\times [0\; 1]$ such that the boundary component $S_g \\times \\{ 0\\}$ is geodesic. Here $S_g$ is a closed orien ted surface of genus $g>1$. Fuchsian manifolds are known as toy cases in t he study of geometry of hyperbolic 3-manifolds with boundary. In my talk I will sketch a proof that a compact Fuchsian manifold with convex boundary is uniquely determined by the induced path metric on $S_g \\times \\{1\\} $. We do not put further restrictions on the boundary except convexity. Th is unifies two previously known results: in the case of smooth boundary su ch a result follows from a work of Schlenker and in the case of polyhedral boundary it was proven by Fillastre.\n LOCATION:https://researchseminars.org/talk/Geometry/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Gabriel Calsamiglia (Universidade Federal Fluminense) DTSTART:20200616T140000Z DTEND:20200616T150000Z DTSTAMP:20260422T225704Z UID:Geometry/3 DESCRIPTION:Title: Spaces of isoperiodic holomorphic and meromorphic differentials\nby G abriel Calsamiglia (Universidade Federal Fluminense) as part of Pangolin s eminar\n\n\nAbstract\nI will present some results on the topology of the s paces of holomorphic and meromorphic one forms over complex curves for whi ch integration along certain homology classes is constant.\n LOCATION:https://researchseminars.org/talk/Geometry/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Andrea Seppi (Université Grenoble Alpes) DTSTART:20200714T140000Z DTEND:20200714T150000Z DTSTAMP:20260422T225704Z UID:Geometry/4 DESCRIPTION:Title: The Gauss map for nearly-Fuchsian manifolds\nby Andrea Seppi (Univers ité Grenoble Alpes) as part of Pangolin seminar\n\n\nAbstract\nIn this ta lk we will study the Gauss map for nearly-Fuchsian manifolds\, namely comp lete hyperbolic n-manifolds homeomorphic to HxR\, where H is a closed hype rsurface with principal curvatures smaller than one in absolute value. The Gauss map of such a hypersurface is a Lagrangian equivariant embedding in the space of oriented geodesics of hyperbolic space\, which is known to h ave a natural para-Kähler structure. We will present two characterization s of the Lagrangian equivariant embeddings obtained in this way\, the firs t in terms of the vanishing of the Maslov class\, and the second in terms of orbits of the group of Hamiltonian symplectomorphisms.\n\nThis is joint work with Christian El Emam (Pavia).\n LOCATION:https://researchseminars.org/talk/Geometry/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Dmitry Faifman (Tel-Aviv Universty) DTSTART:20200728T140000Z DTEND:20200728T150000Z DTSTAMP:20260422T225704Z UID:Geometry/6 DESCRIPTION:Title: Intrinsic volumes of submanifolds of normed spaces: How intrinsic are the y?\nby Dmitry Faifman (Tel-Aviv Universty) as part of Pangolin seminar \n\n\nAbstract\nThe intrinsic volumes\, or quermassintegrals\, are certain geometric functionals on sufficiently nice subsets of Euclidean space\, g iven by the coefficients of the volume of an epsilon-tube of the set\, whi ch is a polynomial in epsilon. H. Weyl discovered that their value on a Ri emannian submanifold of Euclidean space is\, remarkably\, an intrinsic inv ariant of the metric. We will consider the setting of a normed space\, whe re the Holmes-Thompson intrinsic volumes are available\, and attempt to ex tend Weyl's result to Finsler submanifolds. \nBased on a joint work with T . Wannerer.\n LOCATION:https://researchseminars.org/talk/Geometry/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Graham Smith (Universidade Federal do Rio de Janeiro) DTSTART:20200630T140000Z DTEND:20200630T150000Z DTSTAMP:20260422T225704Z UID:Geometry/8 DESCRIPTION:Title: On eternal forced mean curvature flows of tori in perturbations of the un it sphere\nby Graham Smith (Universidade Federal do Rio de Janeiro) as part of Pangolin seminar\n\n\nAbstract\nUsing a singular perturbation arg ument based on the work of B. White\, we construct eternal mean curvature flows of tori in perturbations of the standard unit 3-sphere. Besides bein g of interest in the theory of mean curvature flows\, such objects have ap plications in Morse homology theory. A large part of the proof involves th e construction of certain types of functions of Morse-Smale type over the moduli space of Clifford tori. This has interesting potential applications to the theory of Radon transformations. This is joint work with Claudia S alas Mangaño.\n LOCATION:https://researchseminars.org/talk/Geometry/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Gilles Carron (Université de Nantes) DTSTART:20200825T140000Z DTEND:20200825T150000Z DTSTAMP:20260422T225704Z UID:Geometry/9 DESCRIPTION:Title: The index theorem for manifolds with cusps\nby Gilles Carron (Univers ité de Nantes) as part of Pangolin seminar\n\n\nAbstract\nI will speak on the result obtained with W. Ballmann and J. Brüning about index theorem on manifold with cusps :\n\n-Eigenvalues and holonomy. Int. Math. Res. Not . 2003\, no. 12\, 657–665.\n\n-Regularity and index theory for Dirac-Sch rödinger systems with Lipschitz coefficients.\n\nJ. Math. Pures Appl. (9) 89 (2008)\, no. 5\, 429–476.\n\n-Index theorems on manifolds with strai ght ends. Compos. Math. 148 (2012)\, no. 6\, 1897–1968.\n\nI will start with a review of the case of compact manifolds and manifolds with cylindri cal ends (i.e. the work of Atiyah-Patodi-Singer) and then describe the mai n technical difficulties we had to face.\n LOCATION:https://researchseminars.org/talk/Geometry/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Martín Reiris (Universidad de la República\, Montevideo) DTSTART:20200908T133000Z DTEND:20200908T143000Z DTSTAMP:20260422T225704Z UID:Geometry/10 DESCRIPTION:Title: On the existence of Killing fields in smooth spacetimes with a compact C auchy horizon\nby Martín Reiris (Universidad de la República\, Monte video) as part of Pangolin seminar\n\n\nAbstract\nWe prove that the surfac e gravity of a compact non-degenerate Cauchy horizon in a smooth vacuum sp acetime\, can be normalized to a non-zero constant. This result\, combined with a recent result by Oliver Petersen and István Rácz\, end up provin g the Isenberg-Moncrief\nconjecture on the existence of Killing fields\, i n the smooth differentiability class. The well known corollary of this\, i n accordance with the strong cosmic censorship conjecture\, is that the pr esence of compact Cauchy horizons is a non-generic phenomenon.\nThough we work in 3+1\, the result is valid line by line in any n+1-dimensions.\n LOCATION:https://researchseminars.org/talk/Geometry/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Thibault Leveufre (Université Paris-Sud) DTSTART:20200922T140000Z DTEND:20200922T150000Z DTSTAMP:20260422T225704Z UID:Geometry/11 DESCRIPTION:Title: Marked length spectrum\, geodesic stretch and pressure metric\nby Th ibault Leveufre (Université Paris-Sud) as part of Pangolin seminar\n\n\nA bstract\nThe marked length spectrum of a negatively-curved manifold is t he data of all the lengths of closed geodesics\, marked by the free homoto py of the manifold. The marked length spectrum conjecture (also known as t he Burns-Katok conjecture\, 1985) asserts that two negatively-curved manif olds with same marked length spectrum should be isometric. This conjecture was proved on surfaces (Croke '90\, Otal '90) but remains open in higher dimensions. I will present a proof of a local version of this conjecture\, based on the notions of geodesic stretch and pressure metric (a gener alization of the Weil-Petersson metric to the context of variable curvatur e). Some elements of the theory of Pollicott-Ruelle resonances and anisotr opic spaces will also be needed (I will recall everything). Joint work wit h C. Guillarmou and G. Knieper.\n LOCATION:https://researchseminars.org/talk/Geometry/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Stéphane Sabourau (Université Parsi-Est Créteil) DTSTART:20201006T140000Z DTEND:20201006T150000Z DTSTAMP:20260422T225704Z UID:Geometry/12 DESCRIPTION:Title: Geometric semi-norms in homology\nby Stéphane Sabourau (Université Parsi-Est Créteil) as part of Pangolin seminar\n\n\nAbstract\nThe simpli cial volume of a simplicial complex is a topological invariant related to the growth of the fundamental group\, which gives rise to a semi-norm in h omology. In this talk\, we introduce the volume entropy semi-norm\, which is also related to the growth of the fundamental group of simplicial compl exes and shares functorial properties with the simplicial volume. Answerin g a question of Gromov\, we prove that the volume entropy semi-norm is equ ivalent to the simplicial volume semi-norm in every dimension. Joint work with I. Babenko.\n LOCATION:https://researchseminars.org/talk/Geometry/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Filippo Mazzoli (University of Virginia) DTSTART:20201103T140000Z DTEND:20201103T150000Z DTSTAMP:20260422T225704Z UID:Geometry/13 DESCRIPTION:Title: Constant Gaussian curvature surfaces in hyperbolic 3-manifolds\nby F ilippo Mazzoli (University of Virginia) as part of Pangolin seminar\n\n\nA bstract\nIn this talk I will describe how constant Gaussian curvature (CGC ) surfaces interpolate the structures of the pleated boundary of the conve x core and of the boundary at infinity of a geometrically finite hyperboli c end\, and I will present a series of consequences of this phenomenon: a description of the renormalized volume of a quasi-Fuchsian manifold in ter ms of its CGC-foliation\, a characterization of the immersion data of CGC- surfaces of a hyperbolic end as an integral curve of a time-dependent Hami ltonian vector field on the cotangent space to Teichmüller space\, and a consequent generalization of McMullen’s Kleinian reciprocity theorem.\n LOCATION:https://researchseminars.org/talk/Geometry/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Bruno Premoselli (Université Libre de Bruxelles) DTSTART:20201020T140000Z DTEND:20201020T150000Z DTSTAMP:20260422T225704Z UID:Geometry/14 DESCRIPTION:Title: Glueing constructions of Compact Einstein four-manifolds with negative s ectional\nby Bruno Premoselli (Université Libre de Bruxelles) as part of Pangolin seminar\n\n\nAbstract\nWe construct examples of closed Einste in four-manifolds with negative sectional curvature. We describe two main families of examples which are respectively obtained as ramified covers an d smooth quotients of ``large’’ hyperbolic 4-manifolds with symmetries . The first family of examples is sometimes referred to as Gromov-Thurston manifolds. The Einstein metrics that we construct are the result of a glu eing procedure. They are obtained as deformations of an approximate Einste in metric which is an interpolation between a ``black-hole – type’’ Riemannian Einstein metric near the symmetry locus and the hyperbolic metr ic. This construction yields the first example of compact Einstein manifo lds with negative sectional curvature which are not locally homogeneous. T his is a joint work with J. Fine (ULB\, Brussels).\n LOCATION:https://researchseminars.org/talk/Geometry/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Duc-Manh Nguyen (Université de Bordeaux) DTSTART:20201117T140000Z DTEND:20201117T150000Z DTSTAMP:20260422T225704Z UID:Geometry/15 DESCRIPTION:Title: Variation of Hodge structure and enumerating triangulations and quadrang ulations of surfaces\nby Duc-Manh Nguyen (Université de Bordeaux) as part of Pangolin seminar\n\n\nAbstract\nSince the work of Eskin-Okounkov ( in 2001)\, it has been known that in any stratum of translation surfaces t he number of square-tiled surafces constructed from at most n squares gro ws like $c\\pi^{2g}n^d$\, where $d$ is the (complex) dimension of the stra tum\, $g$ is the genus of the surfaces\, and $c$ is a rational number. Sim ilar phenomenon also occurs in strata of quadratic differentials. Counting square-tiled surfaces in a given stratum is more or less the same as coun ting quadrangulations of a topological surface\, with some prescribed cond itions on the singularities and the holonomy of the associated flat metric . More recently\, Engel showed that the asymptotics of the numbers of quad rangulations and triangulations\, satisfying some prescribed conditions at the singularities\, with at most $n$ tiles are of the form $\\alpha n^d$\ , where $\\alpha$ is a constant in $Q[\\pi]$ or $Q[\\sqrt{3}\\pi]$.\nIn th is talk\, we will explain how the asymptotics above can be related to the computation of the volume of some moduli spaces\, and how one can show tha t in some situations the constant $\\alpha$ belongs actually to either $Q\ \cdot\\pi^d$\, or $Q\\cdot(\\sqrt{3}\\pi)^d$ by using tools from complex a lgebraic geometry. This is joint work with Vincent Koziarz.\n LOCATION:https://researchseminars.org/talk/Geometry/15/ END:VEVENT BEGIN:VEVENT SUMMARY:Jérémy Toulisse (Université de Nice-Sophia Antipolis) DTSTART:20201201T140000Z DTEND:20201201T150000Z DTSTAMP:20260422T225704Z UID:Geometry/16 DESCRIPTION:Title: Plateau problem in the pseudo-hyperbolic space\nby Jérémy Toulisse (Université de Nice-Sophia Antipolis) as part of Pangolin seminar\n\n\nA bstract\nThe pseudo-hyperbolic space H^{2\,n} is the pseudo-Riemannian ana logue of the classical hyperbolic space. In this talk\, I will explain how to solve an asymptotic Plateau problem in this space: given a topological circle in the boundary at infinity of H^{2\,n}\, we construct a unique co mplete maximal surface bounded by this circle. This construction relies on Gromov’s theory of pseudo-holomorphic curves. This is a joint work with François Labourie and Mike Wolf.\n LOCATION:https://researchseminars.org/talk/Geometry/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Ben Lowe (Princeton University) DTSTART:20201215T140000Z DTEND:20201215T150000Z DTSTAMP:20260422T225704Z UID:Geometry/17 DESCRIPTION:Title: Minimal Surfaces in Negatively Curved 3-Manifolds and Dynamics\nby B en Lowe (Princeton University) as part of Pangolin seminar\n\n\nAbstract\n The Grassmann bundle of tangent 2-planes over a closed hyperbolic 3-manifo ld M has a natural foliation by (lifts by their tangent planes of) immerse d totally geodesic planes in M. I am going to talk about work I’ve done on constructing foliations whose leaves are (lifts of) minimal surfaces in a metric on M of negative sectional curvature\, which are deformations of the totally geodesic foliation described above. These foliations make it possible to use homogeneous dynamics to study how closed minimal surfaces in variable negative curvature are distributed in the ambient 3-manifold. Many of the ideas here come from recent work of Calegari-Marques-Neves\, w hich I will also talk about. I was able to establish some preliminary fact s about the dynamics of these foliations\, but much remains to be understo od.\n LOCATION:https://researchseminars.org/talk/Geometry/17/ END:VEVENT BEGIN:VEVENT SUMMARY:Jason Lotay (Oxford University) DTSTART:20210126T150000Z DTEND:20210126T160000Z DTSTAMP:20260422T225704Z UID:Geometry/18 DESCRIPTION:Title: Deformed G2 instantons\nby Jason Lotay (Oxford University) as part o f Pangolin seminar\n\n\nAbstract\nDeformed G2-instantons are special conne ctions occurring in G2 geometry in 7 dimensions. They arise as “mirrors ” to certain calibrated cycles\, providing an analogue to deformed Hermi tian-Yang-Mills connections\, and are critical points of a Chern-Simons-ty pe functional. I will describe an elementary construction of the first non -trivial examples of deformed G2-instantons\, and their relation to 3-Sasa kian geometry\, nearly parallel G2-structures\, isometric G2-structures\, obstructions in deformation theory\, the topology of the moduli space\, an d the Chern-Simons-type functional.\n LOCATION:https://researchseminars.org/talk/Geometry/18/ END:VEVENT BEGIN:VEVENT SUMMARY:Christian El Emam (Université du Luxembourg) DTSTART:20210209T140000Z DTEND:20210209T150000Z DTSTAMP:20260422T225704Z UID:Geometry/19 DESCRIPTION:Title: Families of equivariant immersions in $H^3$ with holomorphic holonomy\nby Christian El Emam (Université du Luxembourg) as part of Pangolin se minar\n\n\nAbstract\nGiven an equivariant immersion of a surface in the hy perbolic 3-space\, a typical problem consists in understanding whether a d eformation of the immersion (parametrized over a complex manifold) produce s a holomorphic deformation of its mondromy in PSL(2\,C). In this talk we present a simple “trick” providing a sufficient condition for this pro perty\, offering for instance an alternative proof of the holomorphicity o f the complex landslide flow. This result is a consequence of the study of immersions into the space of geodesics of the hyperbolic 3-space\, seen a s a holomorphic Riemannian manifold\, whose key features will be discussed in the talk.\n\nThis is joint work with Francesco Bonsante\n LOCATION:https://researchseminars.org/talk/Geometry/19/ END:VEVENT BEGIN:VEVENT SUMMARY:María Asunción Jiménez (Universidade Federal Fluminense) DTSTART:20210223T140000Z DTEND:20210223T150000Z DTSTAMP:20260422T225704Z UID:Geometry/20 DESCRIPTION:Title: Elliptic Linear Weingarten graphs with isolated singularities\nby Ma ría Asunción Jiménez (Universidade Federal Fluminense) as part of Pango lin seminar\n\n\nAbstract\nWe study isolated singularities of graphs whose mean and Gaussian curvature satisfy the elliptic linear relation $2\\alph a H+\\beta K=1$\, $\\alpha^2+\\beta>0$. This family of surfaces includes c onvex and non-convex singular surfaces and also cusp-type surfaces. We det ermine in which cases the singularity is removable\, and classify non-exte ndable totally isolated singularities in term of regular real analytic str ictly convex curves in $\\S^2$. This is a joint work with João P. dos San tos.\n LOCATION:https://researchseminars.org/talk/Geometry/20/ END:VEVENT BEGIN:VEVENT SUMMARY:Barbara Schapira (Université de Rennes I) DTSTART:20210309T140000Z DTEND:20210309T150000Z DTSTAMP:20260422T225704Z UID:Geometry/21 DESCRIPTION:Title: Amenability of covers through critical exponents\nby Barbara Schapir a (Université de Rennes I) as part of Pangolin seminar\n\n\nAbstract\nLet M be a negatively curved manifold. If M is “strongly positively recurre nt”\, i.e. there is a critical gap between its entropy at infinity and i ts entropy\, we show that a cover M' of M is amenable if and only if the c ritical exponents of M' and M coincide. The proof uses a construction of P atterson-Sullivan measures twisted by a representation. This is a joint wo rk with R. Dougall\, R. Coulon and S.Tapie.\n LOCATION:https://researchseminars.org/talk/Geometry/21/ END:VEVENT BEGIN:VEVENT SUMMARY:Louis Merlin (Aachen University) DTSTART:20210323T140000Z DTEND:20210323T150000Z DTSTAMP:20260422T225704Z UID:Geometry/22 DESCRIPTION:Title: On the relations between the universal Teichmuller space and Anti de Sit ter geometry\nby Louis Merlin (Aachen University) as part of Pangolin seminar\n\n\nAbstract\nAnti de Sitter (AdS) space is the Lorentzian cousin of the hyperbolic 3-space: it is a symmetric space with constant curvatur e -1. In this talk\, we will consider surface group representations in the isometry group of AdS space\, called quasi-Fuchsian representations. Ther e is 2 classical objects associated to those representations and one of th e goal is to understand their interplay: the limit set which is a quasi-ci rcle in the boundary at infinity of AdS space and a convex set inside AdS which is preserved by the group action and bounded by two pleated surfaces . I will conclude the talk by a report on a work in common with Jean-marc Schlenker where we extend the "Teichmüller" situation to the "universal T eichmüller".\n LOCATION:https://researchseminars.org/talk/Geometry/22/ END:VEVENT BEGIN:VEVENT SUMMARY:Leon Carvajales (Université de Paris-Sorbonne Université) DTSTART:20210406T133000Z DTEND:20210406T143000Z DTSTAMP:20260422T225704Z UID:Geometry/23 DESCRIPTION:Title: Growth of quadratic forms under Anosov subgroups\nby Leon Carvajales (Université de Paris-Sorbonne Université) as part of Pangolin seminar\n \n\nAbstract\nFor positive integers p and q we define a counting problem i n the (pseudo-Riemannian symmetric) space of quadratic forms of signature (p\,q) on R^{p+q}. This is done by associating to each quadratic form a ge odesic copy of the Riemannian symmetric space of PSO(p\,q) inside the Riem annian symmetric space of PSL_{p+q}(R)\, and by looking at the orbit of th is geodesic copy under the action of a discrete subgroup of PSL_{p+q}(R). We then present some contributions to the study of this counting problem f or Borel-Anosov subgroups of PSL_{p+q}(R).\n LOCATION:https://researchseminars.org/talk/Geometry/23/ END:VEVENT BEGIN:VEVENT SUMMARY:Jean-Marc Schlenker (Université du Luxembourg) DTSTART:20210420T133000Z DTEND:20210420T143000Z DTSTAMP:20260422T225704Z UID:Geometry/24 DESCRIPTION:Title: The Weyl problem for unbounded convex surfaces in H^3\nby Jean-Marc Schlenker (Université du Luxembourg) as part of Pangolin seminar\n\n\nAbs tract\nThe classical Weyl problem in Euclidean space\, solved in the 1950s \, askswhether any smooth metric of positive curvature on the sphere can b e realized as the induced metric on the boundary of a unique convex subset in $\\R^3$. It was extended by Alexandrov to the hyperbolic space\, where a dual problem can also be considered: prescribing the third fundamental form of a convex surface.\n\nWe will describe extensions of the Weyl probl em and its dual to unbounded convex surfaces in $H^3$. Two types of genera lizations can be stated\, one concerning unbounded convex surfaces\, the o ther unbounded locally convex surfaces. Both questions have as special cas es a number of known result or conjectures concerning 3-dimensional hyperb olic geometry\, circle packings\, etc. We will present a rather general ex istence result concerning convex subsets.\n LOCATION:https://researchseminars.org/talk/Geometry/24/ END:VEVENT BEGIN:VEVENT SUMMARY:Matilde Martínez García (Universidad de la República\, Montevid eo) DTSTART:20210504T133000Z DTEND:20210504T143000Z DTSTAMP:20260422T225704Z UID:Geometry/25 DESCRIPTION:Title: On tilings\, amenable equivalence relations and foliated spaces\nby Matilde Martínez García (Universidad de la República\, Montevideo) as p art of Pangolin seminar\n\n\nAbstract\nI will describe a family of foliate d spaces constructed from tylings on Lie groups. They provide a negative a nswer to the following question by G.Hector: are leaves of a compact folia ted space always quasi-isometric to Cayley graphs? Their construction was motivated by a profound conjecture of Giordano\, Putnam and Skau on the cl assification\, up to orbit equivalence\, of actions of countable amenable groups on the Cantor set. I will briefly explain how these examples relate to the GPS conjecture. This is joint work with Fernando Alcalde Cuesta an d Álvaro Lozano Rojo.\n LOCATION:https://researchseminars.org/talk/Geometry/25/ END:VEVENT BEGIN:VEVENT SUMMARY:Barbara Nelli (Università dell’Aquila) DTSTART:20210518T133000Z DTEND:20210518T143000Z DTSTAMP:20260422T225704Z UID:Geometry/26 DESCRIPTION:Title: The topology of constant mean curvature surfaces with convex boundary\nby Barbara Nelli (Università dell’Aquila) as part of Pangolin semina r\n\n\nAbstract\nWe discuss old and new results about the shape of a const ant mean curvature surfaces with strictly convex boundary\, contained in t he halfspace determined by the surface containing the boundary.\n LOCATION:https://researchseminars.org/talk/Geometry/26/ END:VEVENT BEGIN:VEVENT SUMMARY:Maria del Mar Gonzalez\, (Universidad Autónoma de Madrid) DTSTART:20210601T133000Z DTEND:20210601T143000Z DTSTAMP:20260422T225704Z UID:Geometry/27 DESCRIPTION:Title: Singular metrics of constant non-local curvature\nby Maria del Mar G onzalez\, (Universidad Autónoma de Madrid) as part of Pangolin seminar\n\ n\nAbstract\nWe will consider the problem of constructing singular metrics of constant non-local curvature in conformal geometry\, using a gluing sc heme. This non-local curvature is defined from the conformal fractional La placian\, a Paneitz type operator of non-integer order. For the gluing pro cess\, one needs a model solution which is given by the solution of a non- local ODE with good conformal properties. It turns out that conformal geom etry provides powerful tools for the analysis of such equations.\n LOCATION:https://researchseminars.org/talk/Geometry/27/ END:VEVENT BEGIN:VEVENT SUMMARY:Melanie Rupflin (Oxford University) DTSTART:20210615T133000Z DTEND:20210615T143000Z DTSTAMP:20260422T225704Z UID:Geometry/28 DESCRIPTION:Title: Lojasiewicz inequalities near simple bubble trees\nby Melanie Rupfli n (Oxford University) as part of Pangolin seminar\n\n\nAbstract\nIn the st udy of (almost-)critical points of an energy functional one is often confr onted with the problem that a weakly-obtained limiting object does not hav e the same topology. For example sequences of almost-harmonic maps from a surface will in general not converge to a single harmonic map but rather t o a whole bubble tree of harmonic maps\, which cannot be viewed as an obje ct defined on the original domain.\n\nOne of the consequences of this phen omenon is that one of the most powerful tools in the study of (almost-)cri tical points and gradient flows of analytic functionals\, so called Lojasi ewicz-Simon inequalities\, no longer apply.\n\nIn this talk we discuss a m ethod that allows us to prove such Lojasiewicz inequalities for the harmon ic map energy near simple trees and explain how these inequalities allow u s to prove convergence of solutions of the corresponding gradient flow des pite them forming a singularity at infinity.\n LOCATION:https://researchseminars.org/talk/Geometry/28/ END:VEVENT BEGIN:VEVENT SUMMARY:Renato Vianna (Universidade Federal do Rio de Janeiro) DTSTART:20210629T133000Z DTEND:20210629T143000Z DTSTAMP:20260422T225704Z UID:Geometry/29 DESCRIPTION:Title: Sharp Ellipsoid Embeddings and Toric Mutations\nby Renato Vianna (Un iversidade Federal do Rio de Janeiro) as part of Pangolin seminar\n\n\nAbs tract\nIn the study of (almost-)critical points of an energy functional on e is often confronted with the problem that a weakly-obtained limiting obj ect does not have the same topology. For example sequences of almost-harmo nic maps from a surface will in general not converge to a single harmonic map but rather to a whole bubble tree of harmonic maps\, which cannot be v iewed as an object defined on the original domain.\n\nOne of the consequen ces of this phenomenon is that one of the most powerful tools in the study of (almost-)critical points and gradient flows of analytic functionals\, so called Lojasiewicz-Simon inequalities\, no longer apply.\n\nIn this tal k we discuss a method that allows us to prove such Lojasiewicz inequalitie s for the harmonic map energy near simple trees and explain how these ineq ualities allow us to prove convergence of solutions of the corresponding g radient flow despite them forming a singularity at infinity.\n LOCATION:https://researchseminars.org/talk/Geometry/29/ END:VEVENT BEGIN:VEVENT SUMMARY:Misha Belolipetsky (IMPA\, Rio de Janeiro) DTSTART:20210713T133000Z DTEND:20210713T143000Z DTSTAMP:20260422T225704Z UID:Geometry/30 DESCRIPTION:by Misha Belolipetsky (IMPA\, Rio de Janeiro) as part of Pango lin seminar\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/Geometry/30/ END:VEVENT BEGIN:VEVENT SUMMARY:Kathryn Mann (Cornell University) DTSTART:20210921T133000Z DTEND:20210921T143000Z DTSTAMP:20260422T225704Z UID:Geometry/31 DESCRIPTION:by Kathryn Mann (Cornell University) as part of Pangolin semin ar\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/Geometry/31/ END:VEVENT BEGIN:VEVENT SUMMARY:Kathryn Mann (Cornell University) DTSTART:20210928T133000Z DTEND:20210928T143000Z DTSTAMP:20260422T225704Z UID:Geometry/32 DESCRIPTION:Title: How many Anosov flows can you put on a (closed\, hyperbolic) 3 manifold? \nby Kathryn Mann (Cornell University) as part of Pangolin seminar\n\n \nAbstract\nThis question is one part of the puzzle connecting the topolog y and geometry of a manifold to the possible dynamical systems that it sup ports\, in this case the classification problem of Anosov flows.  I will motivate this question and describe some work with Jonathan Bowden constru cting flows on hyperbolic 3-manifolds\, as well as some recent joint work on the classification problem joint with Thomas Barthelme and Steven Frank el.\n LOCATION:https://researchseminars.org/talk/Geometry/32/ END:VEVENT BEGIN:VEVENT SUMMARY:Benoît Kloeckner (Université Paris-Est - Créteil Val-de-Marne) DTSTART:20211012T133000Z DTEND:20211012T143000Z DTSTAMP:20260422T225704Z UID:Geometry/33 DESCRIPTION:Title: Effective high-temperature estimates ensuring a spectral gap\nby Ben oît Kloeckner (Université Paris-Est - Créteil Val-de-Marne) as part of Pangolin seminar\n\n\nAbstract\nThe main goal of the talk shall be to expl ain a few ideas from two classical theories : the thermodynamical formalis m\, and the perturbation of linear operators.\nThe "thermodynamical formal ism" is a framework to describe particular invariant measures of dynamical systems\, called "equilibrium states"\, parametrized by functions on the phase space\, called "potentials". This formalism is based on the "transfe r operator"\; when this operator has a spectral gap\, the equilibrium stat e exists\, is unique\, and has very good statistical properties (exponenti al mixing\, Central Limit Theorem\, etc.)\nIf one perturbs slightly the po tential\, the corresponding transfer operator is also perturbed.\nThe clas sical theory of perturbation of operators ensures that the spectral gap pr operty is an open condition and that under bounded pertubration\, the eige ndata of an operator depends analytically on the perturbation. It turns ou t that using the Implicit Function Theorem\, this theory can be made effec tive with explicit bounds on the size of a neighborhood where the spectral gap persists.\nUsing this effective perturbation theory\, we show complet ely explicit bound on the potential ensuring the spectral gap property for transfert operators of classical families of dynamical systems.\n LOCATION:https://researchseminars.org/talk/Geometry/33/ END:VEVENT BEGIN:VEVENT SUMMARY:Mohammad Ghomi (Georgia Institute of Technology) DTSTART:20211026T133000Z DTEND:20211026T143000Z DTSTAMP:20260422T225704Z UID:Geometry/34 DESCRIPTION:Title: Shortest closed curve to inspect a sphere\nby Mohammad Ghomi (Georgi a Institute of Technology) as part of Pangolin seminar\n\n\nAbstract\nWe s how that in Euclidean 3-space any closed curve which lies outside the uni t sphere and contains the sphere within its convex hull has length at leas t 4Pi. Equality holds only when the curve is composed of 4 semicircles of length Pi\, arranged in the shape of a baseball seam\, as conjectured by V . A. Zalgaller in 1996. This is joint work with James Wenk.\n LOCATION:https://researchseminars.org/talk/Geometry/34/ END:VEVENT BEGIN:VEVENT SUMMARY:Nicolau Saldanha (Pontifícia Universidade Católica\, Rio de Jane iro) DTSTART:20211109T133000Z DTEND:20211109T143000Z DTSTAMP:20260422T225704Z UID:Geometry/35 DESCRIPTION:Title: The homotopy type of spaces of locally convex curves in the sphere\n by Nicolau Saldanha (Pontifícia Universidade Católica\, Rio de Janeiro) as part of Pangolin seminar\n\n\nAbstract\nA smooth curve $\\gamma: [0\,1] \\to S^2$ is locally convex if its geodesic curvature is positive at ever y point. J. A. Little showed that the space of all locally positive curves $\\gamma$ with $\\gamma(0) = \\gamma(1) = e_1$ and $\\gamma'(0) = \\gamma '(1) = e_2$ has three connected components. Our first aim is to describe t he homotopy type of these spaces. One of the connected components is known to be contractible. The two other connected components are homotopically equivalent to $(\\Omega S^3) \\vee S^2 \\vee S^6 \\vee S^{10} \\vee \\cdot s$ and $(\\Omega S^3) \\vee S^4 \\vee S^8 \\vee S^{12} \\vee \\cdots$\, re spectively: we describe the equivalence.\n\nMore generally\, a smooth curv e $\\gamma: [0\,1] \\to S^n$ is locally convex if \\[ \\det(\\gamma(t)\, \ \gamma'(t)\, \\ldots\, \\gamma^{(n)}(t)) > 0 \\] for all $t$. A motivation for considering this space comes from linear ordinary differential equati ons. Again\, we would like to know the homotopy type of the space of local ly convex curves with prescribed initial and final jets. We present severa l partial results.\n\nIncludes joint work with E. Alves\, V. Goulart\, B. Shapiro\, M. Shapiro\, C. Zhou and P. Zuhlke\n LOCATION:https://researchseminars.org/talk/Geometry/35/ END:VEVENT BEGIN:VEVENT SUMMARY:Marie-Amélie Lawn (Imperial College\, London) DTSTART:20211123T133000Z DTEND:20211123T143000Z DTSTAMP:20260422T225704Z UID:Geometry/36 DESCRIPTION:Title: Translating solitons of the mean curvature flow in cohomogeneity one man ifolds\nby Marie-Amélie Lawn (Imperial College\, London) as part of P angolin seminar\n\n\nAbstract\nWe study new examples of translating solito ns of the mean curvature flow. We consider for this purpose manifolds admi tting pseudo-Riemannian submersions and cohomogeneity one actions by isome tries on suitable open subsets. This general setting also covers the well- known classical Euclidean examples of translating solitons invariant by so me group actions. As an application\, we completely classify the rotationa lly invariant translating solitons in Minkowski space.\n LOCATION:https://researchseminars.org/talk/Geometry/36/ END:VEVENT END:VCALENDAR