Tomohide Terasoma
Let C_1 and C_2 be two degenerations of genus g curves. We prove that if two degenerations defines the same conjugacy classes in the mapping class group, they are equivalent under analytic deformations.
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Inspired by an article of Cotti, Dubrovin and Guzzetti arXiv:1706.04808, we extend to a degenerate case a result of Malgrange on integrable deformations of irregular singularities. We give an application to integrable deformations of the solution of some Birkhoff problem and apply it to the construction of Frobenius manifolds.
Logarithmic Equigeneric Smoothing and Maximal Nodal Degenerations
本文研究了曲线和曲面在代数族中的等纲变形问题，提出通过对数半正则性方法在退化情况下保持最大奇点数量的理论，并探讨了其在细化塞弗里计数中的应用。
In this paper we mainly describe $\mathbb{Q}$-Gorenstein smoothings of projective surfaces with only Wahl singularities which have birational fibers. For instance, these degenerations appear in normal degenerations of the projective plane, and in boundary divisors of the KSBA compactification of the moduli space of surfaces of general type [KSB88]. We give an explicit description of them as smooth deformations plus 3-fold birational operations, through the flips and divisorial contractions in [HTU13]. We interpret the continuous part (smooth deformations) as degenerations of certain curves in …
We consider a pair (H,I) where I is an involutive ideal of a Poisson algebra and H lies in I. We show that if I defines a 2n-gon singularity then, under arithmetical conditions on H, any deformation of H can "integrated" as a deformation of (H,I).
We compute local Gromov-Witten invariants of cubic surfaces at all genera. We use a deformation of a cubic surface to a nef toric surface and the deformation invariance of Gromov-Witten invariants.
We prove an analog of Schmid's $\text{\rm SL}_2$-orbit theorem for a class of variations of mixed Hodge structure which includes logarithmic deformations, degenerations of 1-motives and archimedean heights. In particular, as consequence this theorem, we obtain a simple formula for the asymptotic behavior of the archimedean height of a flat family of algebraic cycles which depends only on the weight filtration and local monodromy.
We show that the counting of rational curves on a complete toric variety that are in general position to the toric prime divisors coincides with the counting of certain tropical curves. The proof is algebraic-geometric and relies on degeneration techniques and log deformation theory. This generalizes results of Mikhalkin obtained by different methods in the surface case to arbitrary dimensions.
Let X be a surface with quotient singularities which admits a smoothing to the plane. We prove that X is a deformation of a weighted projective plane P(a^2,b^2,c^2), where a,b,c is a solution of the Markov equation a^2+b^2+c^2=3abc. We also prove a generalisation for del Pezzo surfaces of degree K^2 at least 5.
Let $Q^*$ denote the dual of the quotient bundle on the Grassmannian $G(2,n)$. We prove that the ideal of $Q^*$ in its natural embedding has initial ideal equal to the Stanley-Reisner ideal of a certain unobstructed simplicial complex. Furthermore, we show that the coordinate ring of $Q^*$ has no infinitesimal deformations for $n>5$.
The Caporaso-Harris-Ran degeneration principle: proof and applications
本文研究曲面退化中 Severi 簇的极限，给出 Caporaso-Harris-Ran 退化原理及 Caporaso-Harris 递推公式的完整证明，服务于曲线计数。
Unobstructedness of deformations for a d-semistable central corank one boundary point
针对复阿贝尔曲面的不可约II型退化，本文证明其局部平凡、平坦及对数光滑形变函子均光滑，确立了d-半稳定中心余秩一边界点形变的无阻碍性。
We derive the combinatorial representations of Picard group and deformation space of anti-canonical hypersurfaces of a toric variety using techniques in toric geometry. The mirror cohomology correspondence in the context of mirror symmetry is established for a pair of Calabi-Yau (CY) ${\sf n}$-spaces in toric varieties defined by reflexive polytopes for an arbitrary dimension ${\sf n}$. We further identify the Kahler cone of the toric variety and degeneration cone of CY hypersurfaces, by which the Kahler cone and degeneration cone for a mirror CY pair are interchangeable under mirror symmetry.…
In this paper, we explore the connections between the Minimal Model Program and the theory of Berkovich spaces. Let $k$ be a field of characteristic zero and let $X$ be a smooth and proper $k((t))$-variety with semi-ample canonical divisor. We prove that the essential skeleton of $X$ coincides with the skeleton of any minimal $dlt$-model and that it is a strong deformation retract of the Berkovich analytification of $X$. As an application, we show that the essential skeleton of a Calabi-Yau variety over $k((t))$ is a pseudo-manifold.
Deformations of $(p,q)$-forms and degenerations of the Frölicher spectral sequence
本文研究了复结构形变下Frölicher谱序列的退化性质，给出了固定(p,q)时(p,q)-形式形变无阻碍的微分条件，并建立了保证谱序列各页退化性质形变稳定性的充分条件。
Degenerations of elliptic quartics and K-moduli of Fano threefolds
本文研究经两次爆破构造的法诺三维簇的K-模空间，将其同构于带CM线丛线性化的VGIT商空间，分类了该形变族的K-(半/多)稳定成员，相关证明用到希尔伯特概型几何等新要素。
We give more or less explicit equations for all two-dimensional cusp singularities of embedding dimension at least 4. They are closely related to Felix Klein's equations for universal curves with level n structure. The main technical result is a description of the versal deformation of an n-gon in $P^{n-1}$. The final section contains the equations for smoothings of simple elliptic singularities (of multiplicity at most 9).
There is a large number of different ways of constructing Calabi-Yau manifolds, as well as related non-geometric formulations, relevant in string compactifications. Showcasing this diversity, we discuss explicit deformation families of discretely distinct Hirzebruch hypersurfaces in $\mathbb{P}^n \times \mathbb{P}^1$ and identify their toric counterparts in detail. This precise isomorphism is then used to investigate some of their special divisors of interest, and in particular the secondary deformation family of their Calabi-Yau subspaces. In particular, most of the above so called Hirzebruch…
In this paper we present an example of two polarized K3 surfaces which are not Fundamental Group Equivalent (their fundamental groups of the complement of the branch curves are not isomorphic; denoted by FGE) but the fundamental groups of their related Galois covers are isomorphic. For each surface, we consider a generic projection to CP^2 and a degenerations of the surface into a union of planes - the "pillow" degeneration for the non-prime surface and the "magician" degeneration for the prime surface. We compute the Braid Monodromy Factorization (BMF) of the branch curve of each projected su…
On the behavior of analytic torsion for twisted canonical bundles under degenerations
研究在退化情况下扭曲canonical包的分析扭量行为，证明其对数在判别位形附近具有渐近展开，并提供非等价情况下的系数公式。
Equisingular Deformations of Curves and Surfaces in Threefolds
本文研究曲线和曲面在三维流形中的等奇异变形问题，提出基于变形理论的标准，证明奇点数量由全局可实现性决定，并探讨其在退化情况下的应用。
We study the behaviour of rational curves tangent to a hypersurface under degenerations of the hypersurface. Working within the framework of logarithmic Gromov-Witten theory, we extend the degeneration formula to the logarithmically singular setting, producing a virtual class on the space of maps to the degenerate fibre. We then employ logarithmic deformation theory to express this class as an obstruction bundle integral over the moduli space of ordinary stable maps. This produces new refinements of the logarithmic Gromov-Witten invariants, encoding the degeneration behaviour of tangent curves…
We present some applications of the deformation theory of toric Fano varieties to K-(semi/poly)stability of Fano varieties. First, we present two examples of K-polystable toric Fano 3-fold with obstructed deformations. In one case, the K-moduli spaces and stacks are reducible near the closed point associated to the toric Fano 3-fold, while in the other they are non-reduced near the closed point associated to the toric Fano 3-fold. Second, we study K-stability of the general members of two deformation families of smooth Fano 3-folds by building degenerations to K-polystable toric Fano 3-folds.
We study the boundary of the Milnor fibre of real analytic singularities $f: (\bR^m,0) \to (\bR^k,0)$, $m\geq k$, with an isolated critical value and the Thom $a_f$-property. We define the vanishing zone for $f$ and we give necessary and sufficient conditions for it to be a fibre bundle over the link of the singular set of $f^{-1}(0)$. In the case of singularities of the type $\fgbar: (\bC^n,0) \to (\bC,0)$ with an isoalted critical value, $f, g$ holomorphic, we further describe the degeneration of the boundary of the Milnor fibre to the link of $\fgbar$. As a milestone, we also construct a Lê…
Degeneration of families of projective hypersurfaces and Hodge conjecture
该研究通过维数归纳法，结合光滑超曲面情形的既有结论、混合霍奇模的邻近循环函子等工具，证明了光滑复射影簇的霍奇猜想。
Spectrum of singularities, analytic torsion and Calabi--Yau degenerations
本文通过解析挠率将奇点谱与Calabi--Yau退化几何相联系，提出高阶Durfee--Saito猜想，并利用挠率公式给出双有理光滑填充的障碍，推广了Voisin的结果。
Deformation of rational singularities and Hodge structure
本文证明了在中心纤维具有有理奇点等条件下，一参数退化中前沿 Hodge 数的不变性，并通过计算诱导 $V$-滤除揭示了其与结构层上同调维数不变性的等价性及局部单值群幂零阶数的性质。
We prove the logarithmic divergence of equivariant analytic torsion for one-parameter degenerations of projective algebraic manifolds, when the coefficient vector bundle is given by a Nakano semi-positive vector bundle twisted by the relative canonical bundle.
Meromorphic degeneration of rational functions over snc models of the projective line
本文研究单位穿孔圆盘上解析族在原点亚纯退化时于 snc 模型上的极限测度，证明其等于由该族诱导的非阿基米德有理函数的典范测度前推，推广了 DeMarco-Faber 与 Okuyama 的结论。
From amoebas to pluripotential theory on hybrid analytic spaces
本文讲义介绍非阿基米德几何在复代数簇亚纯退化中的应用，讨论混合空间及复与非阿基米德多重位势理论的相互作用，并总结psh度量收敛性与Monge-Ampere测度的关系。
Degenerations, contractions and deformations of various algebraic structures play an important role in mathematics and physics. There are many different definitions and special cases of these notions. We try to give a general definition which unifies these notions and shows the connections among them. Here we focus on contractions of Lie algebras and algebraic groups.
In this paper, we study a deformation theory of rigid analytic spaces. We develop a theory of cotangent complexes for rigid geometry which fits in with our deformations. We then use the complexes to give a cohomological description of infinitesimal deformation of rigid analytic spaces. Moreover, we will prove an existence of a formal versal family for a proper rigid analytic space.
Let $π: \mathcal{X}^* \rightarrow B^*$ be an algebraic family of compact Kähler manifolds of complex dimension $n$ with negative first Chern class over a punctured disc $B^*\in \mathbb{C}$. Let $g_t$ be the unique Kähler-Einstein metric on $\mathcal{X}_t= π^{-1}(t)$. We show that as $t\rightarrow 0$, $(\mathcal{X}_t, g_t)$ converges in pointed Gromov-Hausdorff topology to a unique finite disjoint union of complete metric length spaces $\coprod_{α=1}^\mathcal{A} (Y_α, d_α)$ without loss of volume. Each $(Y_α, d_α)$ is a smooth open Kähler-Einstein manifold of complex dimension n outside its clo…
The theory of modular deformations is generalized for the category of complex analytic polyhedra which includes germs of complex space as well as any compact complex analytic space. The objective of the theory is a construction of fine moduli spaces. We also discuss new examples of modular families obtained by means of a computer algebra program.
On deformations of foliated complex analytic structures I: Theorems of existence and completeness
本文基于Kodaira-Spencer理论，证明了由切丛或余切丛局部自由子层定义的叶状复解析结构形变的存在性与完备性定理，并推广至同时形变情形。
On deformations of foliated complex analytic structures II: Functors of Artin rings
本文以Artin环函子为框架，研究叶状非奇异簇的形变，识别一阶形变与障碍。
We show that every compact complex analytic space endowed with a fine logarithmic structure and every morphism between such spaces admit a semi-universal deformation. These results generalize the analogous results in complex analytic geometry first independently proved by A. Douady and H. Grauert in the '70. We follow Douady's two steps process approach consisting of an infinite-dimensional construction of the semi-universal deformation space followed by a finite-dimensional reduction.
We consider three examples of families of curves over a non-archimedean valued field which admit a non-trivial group action. These equivariant deformation spaces can be described by algebraic parameters (in the equation of the curve), or by rigid-analytic parameters (in the Schottky group of the curve). We study the relation between these parameters as rigid-analytic self-maps of the disk.
A generalized Tate curve is a universal family of curves with fixed genus and degeneration data which becomes Schottky uniformized Riemann surfaces and Mumford curves by specializing moduli and deformation parameters. By considering each generalized Tate curve as a family of degenerating Riemann surfaces, we give explicit formulas of the period isomorphism between its de Rham and Betti cohomology groups, and of the associated objects: Gauss-Manin connection, variation of Hodge structure and monodromy weight filtration. A remarkable fact is that similar formulas hold also for families of Mumfor…
By analytic deformations of complex structures, we mean perturbations of the Dolbeault operator. By algebraic deformations of complex structures, we mean deformations of holomorphic glueing data. For complex manifolds there is, infinitesimally, a correspondence between these two types deformations. In this article we argue that an analogous correspondence holds between the analytic and algebraic deformations of a super Riemann surface.
Let $M$ be a compact complex manifold equipped with a hyperkähler metric, and $X$ be a closed complex analytic subvariety of $M$. In alg-geom/9403006, we proved that $X$ is trianalytic, i. e., complex analytic with respect to all complex structures induced by the hyperkähler structure, provided that $M$ is generic in its deformation class. Here we study the complex analytic deformations of trianalytic subvarieties. We prove that all deformations of $X$ are trianalytic and naturally isomorphic to $X$ as complex analytic varieties. We show that this isomorphism is compatible with the metric indu…
Tame deformations of highly singular function germs
本文研究具有非孤立奇点轨迹的实解析函数形变，给出了保证其纤维恒常性的解析与代数条件。
On deformations of foliated complex analytic structures III: Unfoldings
本文研究由余切层局部自由子层定义的叶状复解析结构的展开，证明其单参数族展开的存在性与完备性定理，以阿廷环函子语言给出非奇异叶状簇的展开并确定一阶展开与阻碍。
Smoothing toroidal crossing spaces
本文在温和假设下证明环面交叉空间的平滑化存在性，通过研究余维二子空间上不相干的对数结构并证明Hodge-de Rham退化定理，结合BV理论获得平滑化，可用于构造新Calabi-Yau和Fano流形。
Nodal degeneration of chiral algebras II: Local structure and chiral Zhu algebras
本文通过几何构造将顶点代数的Zhu代数推广到因子化代数，定义了一个导出结合代数及其手性双模，并证明其零阶同调恢复节点处顶点代数的模式转移代数。
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