Morningside Center of Mathematics

Chinese Academy of Sciences

MCM Members Seminar

10:30am, Each Thursday

**Speaker**: Dr. Ka-Fai Li (MCM)

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

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

**Place**: ZOOM (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.

**Speaker**: Dr. Yangyu Fan (MCM)

**Title**: *p*-adic Gross-Zagier formula

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

**Place**: MCM110 & 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.

**Speaker**: Dr. Cong Ding (MCM)

**Title**: Complex submanifolds with splitting tangent sequences in rational homogeneous spaces of Picard number one

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

**Place**: MCM110 & ZOOM (Zoom ID: 466 356 2952 Password: mcm1234)

**Abstract**: In 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.

**Speaker**: Dr. Yupeng Wang (MCM)

**Title**: A 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)

**Abstract**: The 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.

**Speaker**: Dr. Jun Wang (MCM)

**Title**: Sharifi's conjectures and generalizations

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

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

**Abstract**: R. 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.

**Speaker**: Prof. Xu Shen (MCM)

**Title**: Harder-Narasimhan strata and p-adic period domains

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

**Place**: MCM110

**Abstract**: In 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.

**Speaker**: Prof. Baohua Fu (MCM)

**Title**: Rigidity of wonderful group compactifications under Fano deformations

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

**Place**: MCM110

**Abstract**: For 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).

**Speaker**: Dr. Peng Yu (MCM)

**Title**: CM value formula for orthogonal Shimura variety with application to lambda invariant

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

**Place**: MCM110

**Abstract**: In 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.

**Speaker**: Dr. Alexandre Pyvovarov (MCM)

**Title**: Bernstein Centre

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

**Place**: MCM110

**Abstract**: Let $F$ 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 $\mathrm{Spec}\: \mathfrak{Z}_{\Omega}$.

**Speaker**: Dr. Hao Zhang (MCM)

**Title**: An introduction to Dwork theory

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

**Place**: MCM110

**Abstract**: In 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.

**Speaker**: Prof. Laurent Fargues (MCM)

**Title**: An Arithmetic Analog of the Abel Jacobi Morphism

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

**Place**: N224

**Abstract**: Global 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.

**Speaker**: Dr. Ka-Fai Li (MCM)

**Title**: Some curvature flows on compact complex manifolds

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

**Place**: MCM110

**Abstract**: In 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.

**Speaker**: Dr. Bingyu Xia (MCM)

**Title**: A generalized Quot scheme for objects in derived category

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

**Place**: MCM110

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

**Speaker**: Dr. Yewon Jeong (MCM)

**Title**: Several types of cubic hypersurfaces with degenerate Gauss map

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

**Place**: MCM110

**Abstract**: Given 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.

**Speaker**: Dr. Bin Zhao (MCM)

**Title**: Spectral Halo of Eigencurves

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

**Place**: MCM110

**Abstract**: In 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)

**Title**: Determine varieties via hypersurfaces

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

**Place**: MCM110

**Abstract**: It 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)

**Title**: Stark-Heegner cycles for Bianchi modular forms

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

**Place**: MCM110

**Abstract**: In 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)

**Title**: Local model of Shimura varieties in $\Gamma_0(p)$ and $\Gamma_1(p)$ levels

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

**Place**: MCM110

**Abstract**: Local 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)

**Title**: Katz p-adic L-function

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

**Place**: MCM110

**Abstract**: Let $E$ 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)

**Title**: Geometric realization of T-shaped root systems and the Jacobians of del Pezzo surfaces

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

**Place**: MCM110

**Abstract**: It 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)

**Title**: Cuspidality Criterion

**Time**: 15:30-16:30, Jan 17, 2019

**Place**: N817

**Abstract**: In 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)

**Title**: Iwasawa theory and Bloch-Kato conjecture for unitary groups

**Time**: 15:30-16:30, Jan 10, 2019

**Place**: N817

**Abstract**: We 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)

**Title**: Introduction to Heegner Points

**Time**: 15:30-16:30, Jan 3, 2019

**Place**: N817

**Abstract**: We introduce the basic arithmetic theory of Heegner points and some applications.

**Speaker**: Prof. Yongquan Hu (MCM)

**Title**: Mop p cohomology of Shimura curves

**Time**: 15:30-16:30, Dec 20, 2018

**Place**: N817

**Abstract**: At 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)

**Title**: Newton strata for good reductions of Shimura varieties of orthogonal type

**Time**: 15:30-16:30, Dec 13, 2018

**Place**: N817

**Abstract**: In 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)

**Title**: On Fano complete intersections in rational homogeneous varieties

**Time**: 15:30-16:30, Dec 6, 2018

**Place**: N817

**Abstract**: Complete 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).

**Speaker**：Prof. Baohua Fu（MCM）

**Title**：Equivariant compactifications of vector groups

**Time**：9:30am, March 28, 2018

**Place**：N817

**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.

**Speaker**：Dr. Qinbo Chen（MCM）

**Title**：Gevrey genericity of Arnold diffusion

**Time**：9:30am, March 21, 2018

**Place**：N817

**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.

**Speaker**：Prof. Xin Wan（MCM）

**Title**：BSD conjecture and generalizations

**Time**：9:30am, March 14, 2018

**Place**：N817

**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.

**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.