### MCM Members Seminar

##### MCM110

Members and postdoctors of Morningside Center of Mathematics will present their current work

in this seminar on each Thursday, 10:30-11:30am.

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SpeakerProf. Weizhe Zheng (MCM)

Title  Ultraproduct cohomology and the decomposition theorem

Time: 10:30-11:30am, April 15, 2021

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract  Ultraproducts of étale cohomology provide a large family of Weil cohomology theories for algebraic varieties. Their properties are closely related to questions of l-independence and torsion-freeness of l-adic cohomology. I will present recent progress in ultraproduct cohomology with coefficients, such as the decomposition theorem, and applications to l-adic cohomology. This talk is based on joint work with Anna Cadoret.

（观看直播请使用森云110直播系统，Zoom仅提供线上互动提问环节）

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SpeakerProf. Song Wang (MCM)

Title Minkwoski-Siegel Formula

Time: 10:30-11:30am, April 8, 2021

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract  In this talk we will survey the Minkowski-Siegel Formula which interprets the average number of the integral solutions of ternery quadratic forms among a genus class in terms of various quantities such as local densities.

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SpeakerProf. Xu Shen (MCM)

Title An introduction to diamonds

Time: 10:30-11:30am, April 1, 2021

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract  We give a brief and example-based introduction to Scholze's theory of diamonds, which plays a fundamental role in the recent work of Fargues-Scholze on the geometrization of local Langlands correspondences.

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SpeakerProf. Ye Tian (MCM)

Title Distribution problem on elliptic curves

Time: 10:30-11:30am, Mar. 25, 2021

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract  In this talk, we review distribution problems of elliptic curves over a fixed number field.

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SpeakerProf. Xin Wan (MCM)

Title BSD formula for general weight modular forms of rank 0 and 1

Time: 10:30-11:30am, Mar. 18, 2021

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract We present a joint work with Jetchev and Skinner to prove BSD formula for modular forms of general weight and analytic rank 0 or 1. This generalizes our previous work for elliptic curves. We also explain the new techniques used in the argument. The rank 0 case is deduced from rank 1 case without using cyclotomic Iwasawa theory.

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Speaker: Prof. Yongquan Hu (MCM)

TitleOn a generalization of Colmez's functor

Time: 10:30-11:30am, Mar. 11, 2021

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract In 2005, Colmez defined an exact functor from the category of finite length admissible smooth representations of GL_2(Q_p) over a field of characteristic p to the category of finite length continuous representations of the absolute Galois group of Q_p. This functor has played a crucial role in the p-adic Langlands program for GL_2(Q_p). In this talk, I will review the construction of Colmez’s functor, and discuss a generalization due to Breuil. If time permits, I will explain the proof of the exactness of this generalized functor. This is a joint work with Breuil, Herzig, Morra and Schraen.

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Speaker: Prof. Baohua Fu (MCM)

Title Isolated symplectic singularities

Time: 10:30-11:30am, Jan. 21, 2021

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract In 2000, Beauville introduced symplectic singularities, as an analogue of hyperkahler among rational singularities. Basic examples include singularities in finite symplectic quotients and in nilpotent orbit closures.  As the simplest case, isolated symplectic singularities are very interesting and connected to the Lebrun-Salamon conjecture, while there are very few such examples. Are there any new examples? I will report some recent progress.

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SpeakerDr.  Yewon Jeong (MCM)

Title Several types of dual defective cubic hypersurfaces

Time: 10:30-11:30am, Jan. 14, 2021

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

AbstractGiven a hypersurface X=V(f) in a complex projective space, we say X is dual defective if the Gauss map of X, the restriction of the gradient map of f on X, has positive dimensional fibers. Especially for cubics, there is an interesting classification of them. We will study several types of dual defective cubic hypersurfaces and the relation between them.

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Speaker: Dr. Bin Zhao (MCM)

TitleSlopes of modular forms

Time10:30-11:30am, Jan. 7, 2021

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract: In this talk, I will first explain the motivation to study the slopes of modular forms. Then I will explain a conjecture raised by Bergdall and Pollack which gives an effective algorithm to compute the slopes of modular forms and give some important consequences of this conjecture. I will talk about some strategies to prove this conjecture if time permits. This is a joint work in progress with Ruochuan Liu, Nha Truong and Liang Xiao.

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SpeakerDr.  Hao Zhang  (MCM)

Title The p-adic Gelfand-Kapranov-Zelevinsky hypergeometric complex

Time: 10:30-11:30am, Dec. 31, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract:In this talk, I will go over our construction of p-adic GKZ-hypergeometric complex. Itis a twisted logarithmic de-Rham complex describing the variation of a family of exponential sums. Using rigid cohomology and arithmetic D-module theory, we study finiteness properties and holonomicity of this complex.

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SpeakerDr.  Bingyu Xia  (MCM)

Title Bridgeland stability condition on surfaces with curves of negative self-intersection

Time: 10:30-11:30am, Dec. 24, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract: I will explain some background motivation in birational geometry, and construct stability conditions for surfaces containing a curve whose self-intersection is negative. This is joint work with R. Tramel.

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SpeakerDr.  Alexandre Pyvovarov  (MCM)

Title Generic smooth representations

Time: 10:30-11:30am, Dec. 17, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract: Let $F$ be a non-archimedean local field. In this talk we will explore genericity of irreducible smooth representations of $GL_n(F)$ by restriction to a maximal compact subgroup $K$ of $GL_n(F)$. Let $(J, \lambda)$ be a Bushnell--Kutzko type for a Bernstein component $\Omega$. The work of Schneider--Zink gives an irreducible $K$-representation $\sigma_{min}(\lambda)$, which appears with multiplicity one in $\mathrm{Ind}_J^K \lambda$. Let $\pi$ be an irreducible smooth representation of $GL_n(F)$ in $\Omega$. We will prove that $\pi$ is generic if and only if $\sigma_{min}(\lambda)$ is contained in $\pi$, in which case it occurs with multiplicity one.

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SpeakerDr.  Renjie Lyu  (MCM)

TitleCubic hypersurfaces: Chow groups, motives and rationality problems

Time: 10:30-11:30am, Dec. 10, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract:  The Chow group of algebraic varieties is extensively used to study the rationality problem. In this talk, I will talk about two results. One is called the universal generation of the Chow groups of smooth cubic hypersurfaces. It studies the cylinder homomorphism on the Chow group by the Fano correspondence. Another is a relation of Chow motives between a smooth cubic hypersurface and its Fano variety of lines. The proof is built upon an observation due to Galkin and Shinder to study the Grothendieck ring of varieties. Besides, I will show applications of the results to integral Hodge(Tate) conjectures.

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SpeakerDr.  Yu Min  (MCM)

TitleIntegral p-adic Hodge theory of formal schemes in low ramification

Time: 10:30-11:30am, Dec. 3, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract: In this talk, I will briefly review the theory of prismatic cohomology and talk about some results concerning the module structure of prismatic cohomology groups. Then I will discuss their applications in the study of the integral comparison theorem and the degeneration of the (integral) Hodge-to-de Rham spectral sequence.

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SpeakerDr.  Dongming She  (MCM)

TitleLocal Langlands correspondence for the twisted exterior and symmetric square epsilon-factors of GL(N)

Time: 10:30-11:30am, Nov. 26, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract: We will introduce the local Langlands correspondence, the Langlands-Shahidi method, and sketch the proof of the equality of the twisted symmetric and exterior square local arithmetic and analytic L- and epsilon-factors of GL(N) over a p-adic field. We use GSpin groups to define these twisted local analytic factors via Langlands-Shahidi method. The proof uses some globalization method to reduce it to the stability of the corresponding analytic gamma-factors, whose proof is given by some analysis of the asymptotic behavior of certain partial Bessel functions.

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SpeakerDr. Arnaud Plessis  (MCM)

TitleOn a conjecture of R\'emond.

Time: 10:30-11:30am, Nov. 19, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract: A R\'emomd conjecture predicts that the points of small height in G(k(Gamma)), when G is either G_m^n or an abelian variety defined over a number field k and Gamma a subgroup of G(\overline{k}) of finite rank, lie in the saturated group of Gamma. This conjecture is only known in a few cases. I will state them by explaining why it is difficult to get more results concerning this conjecture. Finally, I will talk about my current research, which consists to find a new idea to deal with this problem.

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SpeakerDr. Guhan Venkat  (MCM)

TitleRationality of Stark-Heegner cycles attached to base change Bianchi modular forms

Time: 10:30-11:30am, Nov. 05, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract:Stark–Heegner cycles for Bianchi modular forms, that is automorphic forms for GL(2) over an imaginary quadratic field F, were defined in an earlier joint work with C. Williams (U. of Warwick). These are local cohomology classes in the p-adic Galois representation associated to the Bianchi form. They are conjectured to be the restriction (at p) of global cohomology classes in the (semi–stable) Bloch–Kato Selmer group defined over ring class fields of a relative quadratic extension K/F. In this talk, I will report on an ongoing project about some degenarate cases where this conjecture holds.

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SpeakerProf. Daxin Xu  (MCM)

TitleHypergeometric sheaves for classical groups

Time: 10:30-11:30am, Oct. 29, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract:Recently, Jakob and Yun introduced a new class of p-adic representations called euphotic representations, generalizing simple supercuspidal representations and epipelagic representations. In this talk, we will talk about hypergeometric local systems for classical groups constructed by certain euphotic representations. It is based on my joint work in progress with Masoud Kamgarpour and Lingfei Yi.

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SpeakerDr.  Ka-Fai Li (MCM)

Title: U(n)-invariant metrics and positively curved complete Kahler manifolds.

Time: 10:30-11:30am, Oct. 22, 2020

PlaceZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract:The U(n)-invariant Kahler metrics were studied by Wu-Zheng to construct examples of complete Kahler manifolds with positive holomorphic bisectional curvature. In this talk, we will review Wu-Zheng's construction and discuss the longtime behavior of the Kahler-Ricci flow solution starting from these metrics.

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SpeakerDr.  Yangyu Fan (MCM)

Titlep-adic Gross-Zagier formula

Time: 10:30-11:30am, Oct. 15, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

Abstract:In this talk, I will briefly introduce recent work of D. Disegni on the p-adic Gross-Zagier formula on Shimura curves.

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SpeakerDr.  Cong Ding (MCM)

TitleComplex submanifolds with splitting tangent sequences in rational homogeneous spaces of Picard number one

Time: 10:30-11:30am, Sep. 24, 2020

PlaceMCM110 & ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

AbstractIn this talk, we will present some properties of submanifolds with splitting tangent sequence in irreducible Hermitian symmetric spaces of compact type and more general rational homogeneous spaces of Picard number one.

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SpeakerDr. Yupeng Wang (MCM)

TitleA p-adic Simpson correspondence for rigid analytic varieties

Time: 4:00-5:00pm, Sep. 17, 2020

Place: ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

AbstractThe p-adic Simpson correspondence for proper smooth schemes over Spec(Z_p) was firstly studied by Faltings. Now, let k be a p-adic field. Assume K is the field of p-adic complex numbers. Then we can construct a p-adic Simpson correspondence for a rigid analytic variety X with a liftable good reduction $\mathfrak{X}$ defined over Spf($\mathcal(O)_K$) by constructing a new periods sheaf on X_{pro\'{e}t}.Firstly, we give a new description of Faltings'Extension by using the theory of cotangent complexes. Secondly, we construct the desired sheaf of periods. Nextly, we will prove a decompletion theorem which is used to compute cohomology groups. Finally, we establish the p-adic Simpson correspondence.

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SpeakerDr. Jun Wang (MCM)

TitleSharifi's conjectures and generalizations

Time: 4:00-5:00pm, Sep. 10, 2020

Place: ZOOM  (Zoom ID: 466 356 2952   Password: mcm1234)

AbstractR. Sharifi formulated remarkable conjectures which relate the arithmetic of cyclotomic fields to Eisenstein quotient of the homology groups of modular curves. In this talk, I will give a brief introduction to Sharifi's conjectures. Then I will talk about two generalizations of these conjectures. One is for exceptional eigenspace of modular curves, and the other is for a possible extension of Sharifi's conjecture to Bianchi manifold.  It is work in progress with Sheng-Chi Shih and Emmanuel Lecouturier.

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Speaker: Prof. Xu Shen (MCM)

TitleHarder-Narasimhan strata and p-adic period domains

Time: 10:30-11:30am, Jan. 16, 2020

Place: MCM110

AbstractIn this talk, we will discuss the structures of certain moduli spaces of p-adic Hodge structures. More precisely, we will revisit the Harder-Narasimhan stratification on a p-adic flag variety by the theory of modifications of G-bundles on the Fargues-Fontaine curve.  This allows us to compare the Harder-Narasimhan strata with the Newton strata introduced by Caraiani-Scholze. As a consequence, we get further equivalent conditions in terms of p-adic Hodge-Tate period domains for fully Hodge-Newton decomposable pairs.

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Speaker: Prof. Baohua Fu (MCM)

TitleRigidity of wonderful group compactifications under Fano deformations

Time: 10:30-11:30am, Jan. 9, 2020

Place: MCM110

AbstractFor a complex connected simple linear algebraic group G of adjoint type, De Concini and Procesi constructed its wonderful compactification \bar{G}, which is a smooth Fano G\times G-variety enjoying many interesting properties. Assume G is not of type B3, it is shown that its wonderful compactification \bar{G} is rigid under Fano deformations. Namely, for any family of smooth Fano varieties over a connected base, if one fiber is isomorphic to \bar{G}, then so are all other fibers. This is a joint work with Qifeng Li (KIAS).

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Speaker: Dr. Peng Yu (MCM)

TitleCM value formula for orthogonal Shimura variety with application to lambda invariant

Time: 10:30-11:30am, Jan. 2, 2020

Place: MCM110

AbstractIn 1985, Gross and Zagier discovered a beautiful factorization formula for the norm of difference of singular moduli. This has inspired a lot of interesting work, one of which is the study of CM values of automorphic Green functions on orthogonal or unitary Shimura varieties. Now we generalize the definition of CM cycles beyond the ‘small’ and ‘big’ CM cycles and give a uniform formula in general using the idea of regularized theta lifts. Finally, as an application, we are able to give an explicit factorization formula for the norm of λ((d1+\sqrt{d1})/2) - λ((d2+\sqrt{d2})/2) with λ being the modular lambda invariant under the condition (d1, d2) = 1.

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Speaker: Dr. Alexandre Pyvovarov (MCM)

TitleBernstein Centre

Time: 10:30-11:30am, Dec 26, 2019

Place: MCM110

AbstractLet $F$ be a local non-archimedean field and $\mathcal{O}_F$ its ring of integers. Let $\Omega$ be a Bernstein component of the category of smooth representations of $GL_n(F)$, let $(J, \lambda)$ be a Bushnell-Kutzko $\Omega$-type, and let $\mathfrak{Z}_{\Omega}$ be the centre of the Bernstein component $\Omega$. We will explain how to compute $(\mathrm{c\text{--} Ind}_{GL_n(\mathcal{O}_F)}^{GL_n(F)} \lambda)\otimes_{\mathfrak{Z}_{\Omega}}\kappa(\mathfrak{m})$, where $\kappa(\mathfrak{m})$ is the residue field at maximal ideal $\mathfrak{m}$ of $\mathfrak{Z}_{\Omega}$, and the maximal ideal $\mathfrak{m}$ belongs to a Zariski-dense set in $\mathrm{Spec}\: \mathfrak{Z}_{\Omega}$.

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Speaker: Dr. Hao Zhang (MCM)

TitleAn introduction to Dwork theory

Time: 10:30-11:30am, Dec 19, 2019

Place: MCM110

AbstractIn this talk, I will give an introduction of Dwork theory in studying zeta functions and L-functions. Especially on a comparison theorem between algebraic and analytic Dwork cohomology. And then talk about some applications.

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Speaker: Prof. Laurent Fargues (MCM)

TitleAn Arithmetic Analog of the Abel Jacobi Morphism

Time: 4:00-5:00pm, Dec 13, 2019 (NOT Thursday!)

Place: N224

AbstractGlobal class field theory for function fields can be deduced from the fact that, in high degree, the Abel Jacobi morphism of a proper smooth algebraic curve is a locally trivial fibration in simply connected varieties. I will explain a similar statement in the framework of my geometrisation conjecture of the local Langlands correspondence. Here the curve is the one I defined and studied in my joint work with Fontaine.

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Speaker: Dr. Ka-Fai Li (MCM)

TitleSome curvature flows on compact complex manifolds

Time: 10:30-11:30am, Dec. 5, 2019

Place: MCM110

AbstractIn this talk, we will talk about the Kahler-Ricci flow and Anomaly flow on compact complex manifolds. We will discuss their relation to a parabolic Monge-Ampere equation and their limit behavior.

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Speaker: Dr. Bingyu Xia (MCM)

TitleA generalized Quot scheme for objects in derived category

Time: 10:30-11:30am, Nov. 28, 2019

Place: MCM110

AbstractI will introduce a generalized version of Quot scheme for objects in derived category, and talk about its relation to husks and stable pairs.

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Speaker: Dr. Yewon Jeong (MCM)

TitleSeveral types of cubic hypersurfaces with degenerate Gauss map

Time: 10:30-11:30am, Nov. 21, 2019

Place: MCM110

AbstractGiven a hypersurface X = V ( f ) in a complex projective space, the Gauss map of X can be regarded as the restriction of the gradient map of f on X. We say, the hypersurface X has degenerate Gauss map if general fibers of the Gauss map have positive dimension. Especially for cubic hypersurfaces with degenerate Gauss map, there is an interesting classification of them. We will study several types of cubic hypersurfaces and the relation between them.

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Speaker: Dr. Bin Zhao (MCM)

TitleSpectral Halo of Eigencurves

Time: 10:30-11:30am, Nov. 14, 2019

Place: MCM110

AbstractIn a previous work of Ruochuan Liu, Daqing Wan and Liang Xiao, they proved that over the boundary of the weight disc, most components of the eigencurve are disjoint unions of spaces finite flat over the weight disc. In this talk, I will explain a joint work with Liang Xiao on a refinement of this result. A main ingredient in the proof is a down to earth computation of the projective envelope of a Serre weight.

Speaker: Dr. Jie Liu (MCM)

TitleDetermine varieties via hypersurfaces

Time: 10:30-11:30am, Nov. 7, 2019

Place: MCM110

AbstractIt is a classical problem in algebraic geometry, especially in adjunction theory, to ask which properties of the ambient space can be determined by its ample divisors. In this talk, I will focus on some very explicit examples to show that how the VMRT (varieties of minimal rational tangents) theory can be applied to this problem.

Speaker: Dr. Guhanvenkat Harikumar (MCM)

TitleStark-Heegner cycles for Bianchi modular forms

Time: 10:30-11:30am, Oct 31, 2019

Place: MCM110

AbstractIn his seminal paper in 2001, Henri Darmon came up with a systematic construction of p-adic points, viz. Stark-Heegner points, on elliptic curves over the rationals. In this talk, I will report on the construction of local (p-adic) cohomology classes in the Harris-Taylor-Soudry representation associated to a Bianchi cusp form, building on the ideas of Henri Darmon and Rotger-Seveso. These local cohomology classes are conjecturally the restriction of global cohomology classes in an appropriate Bloch-Kato Selmer group and have consequences towards the Bloch-Kato-Beilinson conjecture as well as Gross-Zagier type results. This is based on a joint work with Chris Williams (University of Warwick).

Speaker: Dr. Shinan Liu (MCM)

TitleLocal model of Shimura varieties in $\Gamma_0(p)$ and $\Gamma_1(p)$ levels

Time: 10:30-11:30am, Oct 24, 2019

Place: MCM110

AbstractLocal models of Shimura varieties are objects defined by linear algebra, which describe singularities of Shimura varieties at bad primes. In this exipository talk, we first give an instroduction to Pappas-Zhu's group-theoretic definition of local model in$\Gamma_0(p)$ level, then we quickly review the work of Haines-Stroh and our work in $\Gamma_1(p)$ level.

Speaker: Dr. Yangyu Fan (MCM)

TitleKatz p-adic L-function

Time: 10:30-11:30am, Oct 17, 2019

Place: MCM110

AbstractLet $E$ be an imaginary quadratic field. When the prime $p$ splits in $E$, Katz constructed a two variable $p$-adic L-function interpolating algebraic critical Hecke L-values over $E$ in 1970's. In this talk, we will introduce some recent results concerning the counter construction in the non-split case.

Speaker: Prof. Shigeru Mukai (MCM)

TitleGeometric realization of T-shaped root systems and the Jacobians of del Pezzo surfaces

Time: 10:30-11:30am, Oct 10, 2019

Place: MCM110

AbstractIt is well known that the blow-up of the projective plane has a Cremona symmetry of the Weyl group of the root system of type E.  This was generalized to a T-shaped Cremona symmetry of higher dimensional multi-projective spaces by Coble and Mukai.  Using this framework I will describe the “Jacobians” of del Pezzo surfaces dP_d, and construct several extremal elliptic fibrations over the d-dimensional projective space.

Speaker: Prof. Song Wang (MCM)

TitleCuspidality Criterion

Time: 15:30-16:30, Jan 17, 2019

Place: N817

AbstractIn this talk we will survey the known modularity and cuspidality cases up to now. In particular, we will survey one of our old work on cuspidality criterion on GL(2) \times GL(3).

Speaker: Prof. Xin Wan (MCM)

TitleIwasawa theory and Bloch-Kato conjecture for unitary groups

Time: 15:30-16:30, Jan 10, 2019

Place: N817

AbstractWe present some recent work on Iwasawa theory for motives corresonding to Galois representations associated to cusp forms on unitary groups over totally real fields twisted by Hecke characters, and some consequences for Bloch-Kato conjectures. We prove that if the central critical value is 0, then the Selmer group has positive rank.

Speaker: Prof. Ye Tian (MCM)

TitleIntroduction to Heegner Points

Time: 15:30-16:30, Jan 3, 2019

Place: N817

AbstractWe introduce the basic arithmetic theory of Heegner points and some applications.

Speaker: Prof. Yongquan Hu (MCM)

TitleMop p cohomology of Shimura curves

Time: 15:30-16:30, Dec 20, 2018

Place: N817

AbstractAt present, the mod p (and p-adic) local Langlands correspondence is only well understood for the group GL2(Qp), but remains mysterious even for GL2 of an unramified extension of Qp. However, the Buzzard-Diamond-Jarvis conjecture and the mod p local-global compatibility for GL2/Q suggest that this hypothetical correspondence may be realized in the cohomology of Shimura curves with characteristic p coefficients, cut out by some modular residual global representation. In the talk, I will report some results on the mod p cohomology of Shimura curves from the point of view of the mod p Langlands program. This is joint work (in progress) with Haoran Wang.

Speaker: Prof. Xu Shen (MCM)

TitleNewton strata for good reductions of Shimura varieties of orthogonal type

Time: 15:30-16:30, Dec 13, 2018

Place: N817

AbstractIn this talk, we will study the arithmetic geometry of the GSpin and SO Shimura varieties, which are special examples of Shimura varieties of abelian type. Over complex numbers, these Shimura varieties are closely related to moduli of hyperkaehler manifolds. Thanks to the works of Kisin and Vasiu, we can talk about smooth reductions of these varieties at good primes. It turns out the geometry over characteristic p is much finer, in the sense that these exist some natural stratifications for the reductions. We will describe all the Newton strata. Joint work with Chao Zhang.

Speaker: Prof. Baohua Fu (MCM)

TitleOn Fano complete intersections in rational homogeneous varieties

Time: 15:30-16:30, Dec 6, 2018

Place: N817

AbstractComplete intersections inside rational homogeneous varieties provide interesting examples of Fano manifolds. We first classify these Fano complete intersections which are locally rigid.  It turns out that most of them are hyperplane sections.  We then classify general hyperplane sections which are quasi-homogeneous. This is a joint work with Chenyu Bai and Laurent Manivel.

Speaker: Dr. Qinbo Chen (MCM)

Title: Convergence of viscosity solutions in the vanishing contact structure problem

Time: 15:30-16:30, Nov 29, 2018

Place: N817

Abstract: I will present a joint work with Hitoshi Ishii, Wei Cheng and Kai Zhao on the vanishing contact structure problem, which focuses on the asymptotic behavior of the viscosity solutions uε of Hamilton-Jacobi equation H (x, Du(x), ε u(x)) =c, as the factor ε goes to zero. It is a natural generalization of the vanishing discount problem which was first studied in a general framework by P.-L. Lions, G. Papanicolaou and S. Varadhan. In this talk, I will first briefly introduce some basic notations and results in Aubry-Mather theory and weak KAM theory. Then I will explain how to characterize the limit solution in terms of Peierls barrier functions and Mather measures from a dynamical viewpoint.

Speaker: Dr. Bin Zhao (MCM)

Title: Slopes of modular forms

Time: 15:30-16:30, Nov 22, 2018

Place: N817

Abstract: In this talk, I will first explain the motivation to study the slopes of modular forms. It has an intimate relation with the study of the geometry of eigencurves. On the boundary of the weight disc, the previous work by Liu-Wan-Xiao gives an almost complete answer to this question. I will then explain a recent joint work in progress with Rufei Ren on the generalization of their result to eigenvarieties for certain Hilbert modular forms.

Speaker: Dr. Hao Zhang (MCM)

Title: The p-adic Gelfand-Kapranov-Zelevinsky Hypergeometric system

Time: 15:30-16:30, Nov 15, 2018

Place: N817

Abstract: To a torus action on a complex vector space, Gelfand, Kapranov and Zelevinsky introduce a system of differential equations, called the GKZ hypergeometric system. Its solutions are GKZ hypergeometric functions. In this talk, we will talk about the p-adic counterpart of the GKZ hypergeometric system, and show how it gives the hypergeometric function over the finite field introduced by Gelfand and Graev.

Speaker: Dr. Alexandre Pyvovarov (MCM)

Title: Some new cases of the Breuil-Schneider conjecture

Time: 15:30-16:30, Nov 8, 2018

Place: N817

Abstract: Let F and E be two finite extensions of Qp such that E is large enough. Let r : Gal(F_bar/F) -> GL_n(E) be a Galois representation. In 2013 Caraiani, Emerton, Gee, Geraghty, Paskunas and Shin have constructed an E -Banach representation V(r) of GL_n(F). The authors have hypothesized that the representation V(r) corresponds to Galois representation r under hypothetical p-adic Langlands correspondence. In this work, we show that, under certain assumptions on r, the locally algebraic vectors of V(r) are isomorphic to an irreducible locally algebraic representation. This locally algebraic representation can be determined explicitly via the classical local Langlands correspondence and the knowledge of the Hodge-Tate weights of the Galois representation. From this we can derive new cases of the Breuil-Schneider conjecture.

Speaker: Dr. Bingyu Xia (MCM)

Title: Hilbert scheme of twisted cubics as simple wall-crossings

Time: 15:30-16:30, Nov 1, 2018

Place: N817

Abstract: Hilbert scheme is introduced by Grothendieck and it played an important role in algebraic geometry. Hilbert scheme of twisted cubics in the projective space P^3 is one of the easiest but nontrivial Hilbert scheme, its geometric structure was first described by Piene and Schlessinger in 1985. In this talk, I will introduce Bridgeland stability conditions on the derived category of the projective space P^3, and use wall-crossing phenomena of stability conditions to reprove Piene and Schlessinger's result.

Speaker: Dr. Yewon Jeong (MCM)

Title: Moduli of second fundamental forms of a nonsingular intersection of two quadrics

Time: 15:30-16:30, Oct 25, 2018

Place: N817

Abstract: In 1979, Griffiths and Harris raised a question on the moduli of second fundamental forms of a projective complex submanifold of codimension two. We will report on our study of the question for complete intersections of two quadrics.

Speaker: Dr. Jie Liu (MCM)

Title: Quasi-polarized Calabi-Yau threefolds

Time: 15:30-16:30, Oct 18, 2018

Place: N817

Abstract: A pair (X,L) is called a quasi-polarized Calabi-Yau threefold if X is Calabi-Yau threefold with at worst Gorenstein canonical singularities and L is a nef and big line bundle. In this talk, I will start by introducing the notion of canonical singularities, and then I will discuss the Fujita type results for (X,L) and their applications to the birational geometry of Fano manifolds with coindex four.

Speaker: Dr. Ka-Fai Li (MCM)

Title: The Kahler-Ricci flow on non-compact manifolds

Time: 15:30-16:30, Oct 11, 2018

Place: N817

Abstract: The Ricci flow was introduced by Hamilton in 1982, it is an intrinsic geometric flow that deforms the metric of a Riemannian manifold according to its Ricci curvature. While the existence and uniqueness of the solution is well-known on compact manifolds, we often need to impose some strong conditions in order to arrive at the same conclusion on non-compact manifolds. In this presentation, we will first discuss the background of the Ricci flow, then we will talk about some existence and uniqueness results on non-compact Kahler manifolds. If time is permitted, we will also discuss their applications.

Speaker: Dr. Peng Yu (MCM)

Title: CM Values Associated to Special Cycles on Shimura Varieties

Time: 9:30, June 6, 2018

Place: N818

Abstract: Kudla has a program inspired by theta functions and the work of Hirzebruch and Zagier in 1976. Its main goal is to prove that the generating functions arisen from certain arithmetic cycles on orthogonal Shimura varieties are actually modular. As part of the program, Kudla also conjectured a formula that relates the height pairing of the arithmetic cycles with some proper cycles with the central derivative of some Siegel Eisenstein series. The infinite part of the height turns out to be CM values of special functions on Shimura varieties. In this talk, I will present the background of the problem and known results on CM values. If time permits, I will further talk about my work on its applications to Siegel 3-fold case.

Speaker: Dr. Hongbo Yin (MCM)

Title: Cube sum problems

Time: 9:30, May 23, 2018

Place: N818

Abstract: In this talk, I will explain my recent joint work with Jie Shu and Xu Song which says that if p is a prime congruent to 2 or 5 mod 9, then at least one of 3p and 3p^2 is cube sum. I will introduce some background of the cube sum problem first and then focus on the proof of our results. As comparison, if time permit, I will also explain the proof of Satge's classical result that if p is a prime congruent to 2 mod 9 then 2p is a cube sum and also the proof of Dasgupta and Voight's work on Sylvester conjecture.

Speaker: Prof. Binyong Sun (MCM)

Title: Cohomological test vectors

Time: 9:30, May 16, 2018

Place: N818

Abstract: Various types of modular symbols provide a powerful tool to study arithmetic of special values of L-functions. The Archimedean behaviors of the modular symbols are captured by certain restriction maps of relative Lie algebra cohomology spaces. We call these restriction maps modular symbols at infinity. The modular symbols are non-zero and of arithmetic interest only when the associated modular symbols at infinity are non-zero. Moreover, the latter holds if and only if certain invariant linear functionals on cohomological representations do not vanish on the minimal K-types (in the sense of Vogan). We will give some examples of invariant linear functionals on cohomological representations which does not vanish on the minimal K-types, including the Rankin-Selberg case GL(n)xGL(n-1).

Speaker: Prof. Xiaokui Yang (MCM)

Title: Positivity notions in complex differential and algebraic geometry

Time: 9:30, May 9, 2018

Place: N818

Abstract: In this presentation, we will describe the relationship between various positivity notions in complex differential geometry and complex algebraic geometry. We derive several new vanishing theorems for partially positive vector bundles. As applications, we characterize uniruled and rationally connected projective manifolds by using partially positive curvature tensors. In particular, we confirm a conjecture of Yau that a compact Kahler manifold with positive holomorphic sectional curvature is projective algebraic and rationally connected.

Speaker: Prof. Song Wang (MCM)

Title: Langlands and Multiplicities

Time: 9:30, May 2, 2018

Place: N818

Abstract: In this talk, we will survey current status on Langlands program, including recent breakthrough made by V. Lafforgue on Langlands parametrizations. Also, topics on multiplicities will also be addressed, and some ideals on constructing cusp forms of multiplicity greater than $1$ on $SO (2 N)$ over function fields.

Main reference: [Laf18] 1803.03791 SHTUKAS FOR REDUCTIVE GROUPS AND LANGLANDS CORRESPONDENCE FOR FUNCTION FIELDS

Speaker: Prof. Ye Tian (MCM)

Title: p-converse theorem for elliptic curves with complex multiplication

Time: 9:30, April 25, 2018

Place: N818

Abstract: Let E be an elliptic curve defined over rationals and p a prime. A theorem of Gross-Zagier and Kolyvagin says that if the L-function of E has vanishing order one at the center then the corank of its p-Selmer group is also one. In a joint work with Burungale, we show the converse to the above result in the case that E has complex multiplication and p>3 is ordinary for E. We will introduce the related concepts via the congruent number problem.

Speaker: Prof. Xu Shen (MCM)

Title: The Fargues-Rapoport conjecture

Time: 9:30, April 18, 2018

Place: N818

Abstract: Complex Shimura varieties arise as discrete quotients of certain Griffiths period domains. But things are quite different in the p-adic world. In this talk, we explain some ideas in the recent joint work with Miaofen Chen and Laurent Fargues on the structure of some p-adic period domains. More precisely, we will sketch a proof of the Fargues-Rapoport conjecture: for a basic local Shimura datum (G,b,μ), the weakly admissible locus coincides with the admissible one if and only if the Kottwitz set B(G, μ) is fully Hodge-Newton decomposable.

Speaker: Prof. Wenwei Li (MCM)

Title: On spherical spaces

Time: 9:30, April 11, 2018

Place: N818

Abstract: Spherical varieties are expected to be a general vehicle for extending Langlands program to a relative setting. Over an algebraically closed field, they have been classified in combinatorial terms by Luna-Vust, extending the well-known theory of toric varieties. In this talk, I plan to survey Wedhorn's recent work on spherical algebraic spaces. If possible, I will also sketch some possible mini-projects in this direction.

Speaker: Prof. Yongquan Hu (MCM)

Title: Asymptotic growth of the cohomology of Bianchi groups

Time: 9:30, April 4 (Wednesday), 2018

Place: N817

Abstract: Given a level N and a weight k, we know the dimension formula of the space of classical modular forms. This turns out to be unknown if we consider Bianchi modular forms, that is, modular forms over imaginary quadratic fields. In this talk, we consider the asymptotic behavior of the dimension when the level is fixed and the weight grows. I will first explain the background of this problem, and an upper bound obtained by Simon Marshall using Emerton's completed cohomology. Then I will explain how to improve this bound using the mod p representation theory of GL2(Qp).

SpeakerProf. Baohua FuMCM

TitleEquivariant compactifications of vector groups

Time9:30am, March 28, 2018

PlaceN817

Abstract: In 1999, Hassett-Tschinkel considered the equivariant version of this propblem obtained the classification up to dim. 3. I'll report recent progress on this (equivariant) problem. In particular, we obtain the classification up to dimension 5.

SpeakerDr. Qinbo ChenMCM

TitleGevrey genericity of Arnold diffusion

Time9:30am, March 21, 2018

PlaceN817

Abstract: It is well known that Arnold diffusion is a typical phenomenon for generic a priori unstable Hamiltonian systems. In this talk, by using variational method, we will show that under generic Gevrey-smooth perturbations, Arnold diffusion still exists in a priori unstable Hamiltonian systems.

SpeakerProf. Xin WanMCM

TitleBSD conjecture and generalizations

Time9:30am, March 14, 2018

PlaceN817

Abstract: We first give a survey on BSD conjecture and what is known about it, especially focus on some recent work on the full BSD formula in the rank 0 and 1 cases. Then we also discuss some generalizations to modular forms.

Speaker: Prof. Weizhe Zheng (MCM)

Title: Around l-independence

Time: 9:30, May 30, 2018

Place: N818

Abstract: Serre and Tate proposed a number of conjectures on the l-independence of l-adic cohomology. I will survey some old and new results around these conjectures.