13 PRIMA 2013 AbstractsRyuhei UeharaJapan Advanced Institute of Science and Technology,Japanuehara@jaist.ac.jpThe graph isomorphism (GI) problem asks whether twogiven graphs are isomorphic or not. Th<strong>at</strong> is, it askswhether there exists a one-to-one mapping between twogiven graphs. The GI problem is quite basic and simple,however, it’s time complexity is a long standing openproblem. The problem is clearly in NP, but it is notknown to be NP-complete or not. The GI problem is oneof candid<strong>at</strong>es between the classes NP and P. The problemhas four aspects from the viewpoints of theoretical computerscience. (1) Wh<strong>at</strong> the comput<strong>at</strong>ional complexityclass th<strong>at</strong> captures the GI problem? (2) How fast can wesolve the problem (in exponential time)? (3) Wh<strong>at</strong> thegraph classes such th<strong>at</strong> the GI problem is still as hardas general graphs? (4) Wh<strong>at</strong> the graph classes such th<strong>at</strong>the GI problem can be solved in polynomial time. In thistalk, I focus on (3) and (4). If we can clarify this gap, itindic<strong>at</strong>es the essential difficulty of the GI problem. Lastfew decades, many graph classes are proposed and investig<strong>at</strong>ed.Among them, we focus on some graph classesth<strong>at</strong> have geometric characteriz<strong>at</strong>ion. Typical examplesare interval graphs, th<strong>at</strong> are intersection graphs of intervals,and chordal graphs, th<strong>at</strong> are intersection graphs ofsubtrees of a tree. The GI problem can be solved in lineartime for interval graphs, while the GI problem forchordal graphs is as hard as general graphs. Some basictechniques to show these results are presented, and Ipresent some graph classes such th<strong>at</strong> the complexity ofthe GI problem are not known.On-line list colouring of graphsXuding ZhuZhejiang Normal University, Chinaxudingzhu@gmail.comThe on-line choice number of a graph is a vari<strong>at</strong>ion of thechoice number defined through a two person game. Givena finite graph G and a mapping f : V (G) → N, two players,the Lister and the Painter, play the on-line (G, f)-listcolouring game defined as follows: In the i-th step, theLister presents a non-empty subset V i of V (G) \ ∪ i−1j=1 X j,and the Painter chooses an independent set X i containedin V i . If v ∈ V i , then we say colour i is a permissiblecolour of vertex v. If v ∈ X i , then we say v is colouredby colour i. If <strong>at</strong> the end of a certain step, a vertex vis given f(v) permissible colours but remains uncoloured,then the game ends and the Lister wins the game. Otherwise,<strong>at</strong> some step, all vertices are coloured, the gameends and the Painter wins the game. We say G is on-linef-choosable if the Painter has a winning str<strong>at</strong>egy in theon-line (G, f)-list colouring game, and we say G is on-linek-choosable if G is on-line f-choosable for the constantfunction f ≡ k. The on-line choice number of G, denotedby χ P (G), is the minimum k for which G is on-linek-choosable. It follows from the definition th<strong>at</strong> for anygraph χ P (G) ≥ ch(G), where ch(G) is the choice numberof G. There are graphs G for which χ P (G) is strictlylarger than ch(G). In particular, there are graphs G with|V (G)| = 2χ(G) + 1 with χ P (G) > χ(G), in contrast toa recently confirmed conjecture of Ohba th<strong>at</strong> every suchgraph has χ(G) = ch(G). It was conjectured by Huang,Wong and Zhu th<strong>at</strong> every graph G with |V (G)| ≤ 2χ(G)has χ P (G) = χ(G). This talk presents some progresson the study of the conjecture, and some results on theupper bounds for the on-line choice number of classes ofgraphs.Special Session 6Geometric AnalysisConvergence of scalar-fl<strong>at</strong> metrics on manifoldswith boundary under the Yamabe flowSérgio AlmarazUniversidade Federal Fluminense, Brazilalmaraz@vm.uff.brIn this talk I will discuss a convergence theorem for aYamabe-type flow on manifolds with boundary. This isa flow th<strong>at</strong> evolves conformal scalar-fl<strong>at</strong> metrics accordingto equ<strong>at</strong>ions envolving the boundary mean curv<strong>at</strong>ure.Convergence to a scalar-fl<strong>at</strong> metric with constant boundarymean curv<strong>at</strong>ure is established assuming either a positivemass theorem or a genetric condition.Curv<strong>at</strong>ure behavior <strong>at</strong> singularity time ofRicci flowXiaodong CaoCornell University, USAcao@m<strong>at</strong>h.cornell.eduIn this talk, we will first survey some known result aboutcurv<strong>at</strong>ure behavior <strong>at</strong> the first finite-singularity time underthe Ricci flow. Then we will discuss some recent developmentin this direction and their applic<strong>at</strong>ions.Complete pseudohermitian manifolds withpositive spectrumShu-Cheng Chang 1 , Jui-Tang Chen 2 & Ting-Jung Kuo 31 N<strong>at</strong>ional Taiwan University, Taiwan, R.O.C.scchang@m<strong>at</strong>h.ntu.edu.tw2 N<strong>at</strong>ional Taiwan Normal University, Taiwan, R.O.C.jtchen@ntnu.edu.tw3 N<strong>at</strong>ional Taiwan University, Taiwantjkuo@ntu.edu.twIn this paper, we study complete noncompact pseudohermitianmanifolds with positive spectrum of the sub-Laplacian. We proved splitting- type theorems for a classof complete noncompact pseudohermitian manifolds withvanishing torsion whose spectrum of the sub-Laplacianhas an optimal positive lower bound. These can be viewedas the CR analogue of theorems of Li-Wang and the equalitycase of a theorem of Cheng.Affine cones over smooth del Pezzo surfacesIvan CheltsovThe University of Edinburgh, UKcheltsov@yahoo.comWe answer neg<strong>at</strong>ively the old question of Misha Zaidenbergand Hubert Flenner by proving th<strong>at</strong> affine cones oversmooth cubic surfaces do not admit non-trivial actions ofthe additive group. Our proof uses the alpha-functionsof smooth del Pezzo surfaces and classical bir<strong>at</strong>ional constructionsth<strong>at</strong> go back to Manin and Serge.Symplectic mean curv<strong>at</strong>ure flow in CP 2Xiaoli HanTsinghua University, Chinahanxiaoli@m<strong>at</strong>h.tsinghua.edu.cnI will give a talk about the symplectic mean curv<strong>at</strong>ureflow in CP 2 . Under some pinching conditions, the symplecticmean curv<strong>at</strong>ure flow exists for long time and convergesto a holomorphic curve.
14 PRIMA 2013 AbstractsRicci flow and 4-manifolds with positiveisotropic curv<strong>at</strong>ureHong HuangBeijing Normal University, Chinahhuang@bnu.edu.cnWe’ll survey the work by Hamilton, Chen, Tang, Zhu andthe speaker on the classific<strong>at</strong>ion of complete 4-manifolds(or orbifolds) with positive isotropic curv<strong>at</strong>ure. The maintool used here is the Hamilton-Perelman theory on Ricciflow with surgery. When we consider noncompact manifoldsor orbifolds we need to adapt the original Hamilton-Perelman theory. We’ll indic<strong>at</strong>e the necessary modific<strong>at</strong>ionsin these cases.Convergence of Calabi flow with small initiald<strong>at</strong>aHaozhao LiUniversity of Science and Technology of China, Chinahzli@ustc.edu.cnWe will discuss the long time existence and convergence ofthe Calabi flow under some small initial conditions withoutassuming the existence of constant scalar curv<strong>at</strong>ureKähler metrics. This is joint work with Kai Zheng.K-stability of Fano varieties and Alpha invariantYuji OdakaKyoto university, Japanyodaka@m<strong>at</strong>h.kyoto-u.ac.jpThe K-stability is first defined by Tian and l<strong>at</strong>er generalizedby Donaldson formally as a positivity of generalizedFutaki invariants. This talk will focus on the case of Fanovarieties.Thanks to the recent celebr<strong>at</strong>ed works of the proofof existence of Kähler-Einstein metrics on K-stable Fanomanifolds due to Chen-Donaldson-Sun and Tian, the K-stability has been finally proved to be equivalent to theexistence of Kähler-Einstein metrics i.e. we can in principlestudy the existence problem algebro-geometrically.However it is in general hard, <strong>at</strong> the moment, to testK-stability.The speaker will review the basic structure of the generalizedFutaki invariants from algebro-geometric viewpointand gives rel<strong>at</strong>ion with (the Minimal modelprogram-based) bir<strong>at</strong>ional geometry, in particular introducingthe notion of “destabilizing subschemes" afterthe wake of Ross-Thomas. This analysis in particularwill give a proof of K-stability of Fano n-fold X withα(X) >n which corresponds to the theorem of Tiann+1in 80s where the alpha invariant α(X) was introduced.This talk will be based on a joint work with Yuji Sano.α-functions of smooth del Pezzo surfacesJihun ParkInstitute for Basic Science & Pohang University of Scienceand Technology, Koreawlog@postech.ac.krWe define α-functions of Fano varieties by considering theα-invariants of G. Tian locally. We demonstr<strong>at</strong>e how toobtain the α-functions of smooth del Pezzo surfaces. Inaddition, their applic<strong>at</strong>ions are briefly introduced.Bergman kernel of a polarized Kähler ALEmanifoldYalong ShiNanjing University, Chinashiyl@nju.edu.cnI shall report some recent joint work with Claudio Arezzoand Alberto Della Vedova on the Bergman kernel of KählerALE manifolds.The first eigenvalue of minimal submanifoldsin an unit sphereZizhou TangBeijing Normal University, ChinaWe will talk about the first eigenvalue of a minimalisoparametric hypersurface in a unit spheres, as well asth<strong>at</strong> of their focal submanifolds. For the special case, weverify Yau’s conjecture.The regularity of limit spaceBing WangUniversity of Wisconsin-Madison, USAbwang@m<strong>at</strong>h.wisc.eduThis is a joint work with Tian. We study the structure ofthe limit space of a sequence of almost Einstein manifolds,which are generaliz<strong>at</strong>ions of Einstein manifolds.Roughlyspeaking, such manifolds are the initial manifolds of somenormalized Ricci flows whose scalar curv<strong>at</strong>ures are almostconstants over space-time in the L 1 -sense, Ricci curv<strong>at</strong>uresare bounded from below <strong>at</strong> the initial time. Underthe non-collapsed condition, we show th<strong>at</strong> the limitspace of a sequence of almost Einstein manifolds has mostproperties which is known for the limit space of Einsteinmanifolds. As applic<strong>at</strong>ions, we can apply our structureresults to study the properties of Kähler manifolds.The limit of the Yang-Mills-Higgs flow onsemi-stable Higgs bundlesJiayu Li & Xi ZhangUniversity of Science and Technology of China, Chinam<strong>at</strong>hzx@ustc.edu.cnIn this talk, we consider the gradient flow of the Yang-Mills-Higgs functional for Higgs pairs on a Hermitianvector bundle (E, H 0 ) over a compact Kähler manifold(M, ω). We study the asymptotic behavior of the Yang-Mills-Higgs flow for Higgs pairs <strong>at</strong> infinity, and show th<strong>at</strong>the limiting Higgs sheaf is isomorphic to the double dualof the graded Higgs sheaves associ<strong>at</strong>ed to the Harder-Narasimhan-Seshadri filtr<strong>at</strong>ion of the initial Higgs bundle.Ricci curv<strong>at</strong>ure in Kahler-Ricci flowZhou ZhangUniversity of Sydney, Australiazhangou@m<strong>at</strong>hs.usyd.edu.auRicci curv<strong>at</strong>ure is a geometric quantity n<strong>at</strong>urally rel<strong>at</strong>edto the behaviour of Ricci flow. In this talk, we discusssome recent results on the rel<strong>at</strong>ions between the variousbounds of Ricci curv<strong>at</strong>ure and the Kähler-Ricci flow existingfor either finite or infinite time.A class of Weingarten curv<strong>at</strong>ure measuresBin ZhouPeking University, Chinabzhou@pku.edu.cn
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- Page 48 and 49: 1 PRIMA 2013 AbstractsContents1 Pub
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