Marzia Polito
We give a complete description of the tautological subgroup of the fourth cohomology group of the moduli space of pointed stable curves, and prove that for g \geq 8 it coincides with the cohomology group itself. We further give a conjectural upper bound depending on the genus for the degree of new tautological relations.
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After a short exposition of the basic properties of the tautological ring of the moduli space of genus g Deligne-Mumford stable curves with n markings, we explain three methods of detecting non-tautological classes in cohomology. The first is via curve counting over finite fields. The second is by obtaining length bounds on the action of the symmetric group S_n on tautological classes. The third is via classical boundary geometry. Several new non-tautological classes are found.
Tautological systems and local cohomology
探讨重言式系统与齐次空间上锥的局部上同调联系，研究其导出版本，表明在诸多情形下它是混合霍奇模复形的基础。
On the cohomology of tautological bundles over Quot schemes of curves
研究曲线商上塔利奥格利 bundles 的外幂和对称幂的上同调消失问题，通过构造具有消失上同调的解析，描述其全局截面空间。
Deligne's weight spectral sequence and tautological cohomology of the moduli space of curves
本文通过计算机程序实现Deligne的重量谱序列，计算标号光滑曲线模空间的有理上同调的重量分级，特别针对 genus 五和 genus 三的情况，研究了边界分层中上同调群由塔罗格类生成时的结构。
Let $N$ be the smallest integer such that there is a non-tautological cohomology class of even degree on $\mathcal{\bar M}_{2,N}$. We remark that there is such a non-tautological class on $\mathcal{\bar M}_{2,20}$, by work of Graber and Pandharipande. We show that $\mathcal{\bar M}_{2,N}$ has non-tautological cohomology only in one degree, which is not the middle degree. In particular, it follows that the tautological ring of $\mathcal{\bar M}_{2,N}$ is not Gorenstein. We present some evidence suggesting that N=20 holds.
We give an algorithmic description of the action of the Chern classes of tautological bundles on the cohomology of Hilbert schemes of points on surfaces within the framework of Nakajima's oscillator algebra. This leads to an identification of the cohomology ring of Hilbert schemes of the affine plane with a ring of differential operators on a Fock space. We end with the computation of the top Segre classes of tautological bundles associated to line bundles on Hilb^n up to n=7, and give a conjecture for the generating series.
Non-trivial and Non-tautological Cohomology of Strata of Differentials
本文通过多尺度微分模空间的边界分层几何，构建了非平凡和非琐碎的上同调类。
We prove that the tautological ring of $M_{2,n}^{ct}$, the moduli space of n-pointed genus two curves of compact type, does not have Poincaré duality for any $n \geq 8$. This result is obtained via a more general study of the cohomology groups of $M_{2,n}^{ct}$. We explain how the cohomology can be decomposed into pieces corresponding to different local systems and how the tautological cohomology can be identified within this decomposition. Our results allow the computation of $H^k(M_{2,n}^{ct})$ for any $k$ and $n$ considered both as $S_n$-representation and as mixed Hodge structure/$\ell$-ad…
We study tautological classes on the moduli space of stable $n$-pointed hyperelliptic curves of genus $g$ with rational tails. Our result gives a complete description of tautological relations. The method is based on the approach of Yin in comparing tautological classes on the moduli of curves and the universal Jacobian. It is proven that all relations come from the Jacobian side. The intersection pairings are shown to be perfect in all degrees. We show that the tautological algebra coincides with its image in cohomology via the cycle class map. The latter is identified with monodromy invarian…
We show that the rational cohomology of the genus zero stable map spaces to SL flag varieties is entirely tautological.
On the Chow and cohomology rings of moduli spaces of stable curves
本文研究稳定曲线模空间 $\overline{\mathcal{M}}_{g,n}$ 的有理 Chow 环与上同调环何时由赘言类生成，并证明若干低亏格、低标记点情形下二者同构且为赘言环。
We prove Getzler's claims about the tautological ring of stable curves of genus one, i.e. that the tautological ring coincides with the even cohomology ring, and that all relations between generators follow from the WDVV relation and Getzler's relation.
Extensions of tautological rings and motivic structures in the cohomology of $\overline{\mathcal{M}}_{g,n}$
本文研究 $\overline{\mathcal{M}}_{g,n}$ 上同调中在重言运算下封闭且包含重言子环的子环族，利用归纳论证证实了 Chenevier–Lannes 关于低次数上同调中伽罗瓦表示与霍奇结构的预测，并证明 $H^4$ 由重言类生成。
We explore the structure of the cohomology ring of the moduli space of stable 1-dimensional sheaves on $\mathbb{P}^2$ of any degree. We obtain a minimal set of tautological generators, which implies an optimal generation result for both the cohomology and the Chow ring of the moduli space. Our approach is through a geometric study of tautological relations.
Non-tautological cycles on moduli spaces of smooth pointed curves
本研究推广了已有方法，证明除有限多组亏格$g$和点数$n$外，光滑带点曲线模空间$\bM_{g,n}$上均存在非上同调代数上同调类，覆盖了绝大多数此前未解决的情形。
We describe the structure of the top tautological group in the cohomology of the moduli space of smooth genus $g$ curves with $n$ marked points.
We present a localization proof of the fact that the cohomology of the moduli spaces of genus zero stable maps to projective spaces is entirely tautological. In addition, we obtain a description of a Bialynicki-Birula stratification in the context of Gathmann's moduli spaces of maps with prescribed contact order to a fixed hyperplane.
Using a simple geometric argument, we obtain an infinite family of nontrivial relations in the tautological ring of $M_g$ (and in fact that of $M_{g,2}$). One immediate consequence of these relations is that the classes $κ_1,...,κ_{[g/3]}$ generate the tautological ring of $M_g$, which has been conjectured by Faber, and recently proven at the level of {\em cohomology} by Morita.
We find a set of generators and relations for the system of extended tautological rings associated to the moduli spaces of stable maps in genus zero, admitting a simple geometrical interpretation. In particular, when the target is $\PP^n$, these give a complete presentation for the cohomology and Chow rings in the cases with/without marked points.
In this paper, our aim is to find the relations amongst the cohomology classes of Brill-Noether subvarieties of the moduli space of semistable bundles over an elliptic curve. We obtain results similar to the Poincaré relations on a Jacobian variety.
We give quantum Pieri rules for quantum cohomology of Grassmannians of classical types, expressing the quantum product of Chern classes of the tautological subbundles with general cohomology classes. We derive them by showing the relevant genus zero, three-pointed Gromov-Witten invariants coincide with certain classical intersection numbers.
To a quiver $Q$ and choices of nonzero scalars $q_i$, non-negative integers $α_i$, and integers $θ_i$ labeling each vertex $i$, Crawley-Boevey--Shaw associate a "multiplicative quiver variety" $\mathcal{M}_θ^q(α)$, a trigonometric analogue of the Nakajima quiver variety associated to $Q$, $α$, and $θ$. We prove that the pure cohomology, in the Hodge-theoretic sense, of the stable locus $\mathcal{M}_θ^q(α)^s$ is generated as a $\mathbb{Q}$-algebra by the tautological characteristic classes. In particular, the pure cohomology of genus $g$ twisted character varieties of $GL_n$ is generated by tau…
Extension Groups of Tautological Bundles on Punctual Quot Schemes of Curves
本文证明了曲线上点态 Quot 概形上重言丛的上同调与扩张群公式，并由此推出重言丛决定原始向量丛的同构类，同时给出沿 Quot--Chow 态射推前的消失结果。
Holomorphic forms and non-tautological cycles on moduli spaces of curves
本文利用曲线模空间上的全纯形式构造新的非重言代数上同调类，推广了Graber–Pandharipande和van Zelm关于双椭圆闭链的工作，证明了无穷多个$\mathcal{M}_{g,n}$及$g=12$和$g\geq16$时$\mathcal{M}_g$上存在非重言类。
Gromov-Witten theory, degenerations, and the tautological ring
该研究开发新的退化技术，结合对数GW理论的重构定理，证明了几类代数簇的GW闭链的tautological性与退化相关猜想，为GW理论与tautological环的关系提供关键证据。
We show that the vanishing of the $(g+1)$-st power of the theta divisor in the cohomology and Chow rings of the universal abelian variety implies, by pulling back along a collection of Abel-Jacobi maps, the vanishing results in the tautological ring of $\mathcal{M}_{g,n}$ of Looijenga, Ionel, Graber-Vakil, and Faber-Pandharipande. We also show that Pixton's double ramification cycle relations, which generalize the theta vanishing relations and were recently proved by the first and third authors, imply Theorem $\star$ of Graber and Vakil. Moreover, our proof provides an algorithm for expressing…
Let $X$ a smooth quasi-projective algebraic surface, $L$ a line bundle on $X$. Let $X^{[n]}$ the Hilbert scheme of $n$ points on $X$ and $L^{[n]}$ the tautological bundle on $X^{[n]}$ naturally associated to the line bundle $L$ on $X$. We explicitely compute the image $\bkrh(L^{[n]})$ of the tautological bundle $L^{[n]}$ for the Bridgeland-King-Reid equivalence $\bkrh : \B{D}^b(X^{[n]}) \ra \B{D}^b_{\perm_n}(X^n)$ in terms of a complex $\comp{\mc{C}}_L$ of $\perm_n$-equivariant sheaves in $\B{D}^b_{\perm_n}(X^n)$. We give, moreover, a characterization of the image $\bkrh(L^{[n]} \tens ... \ten…
Vanishing theorems on wonderful varieties
本文研究了奇妙簇上重言丛的消没定理，证明了Brieskorn结果的类似物及Orlik--Solomon代数的比较定理，扩展了Borel--Weil--Bott型消没定理，并将White基猜想的弱版本归约为上同调消没问题。
Let $V$ be a smooth, projective, convex variety. We define tautological $ψ$ and $κ$ classes on the moduli space of stable maps $\M_{0,n}(V)$, give a (graphical) presentation for these classes in terms of boundary strata, derive differential equations for the generating functions of the Gromov-Witten invariants of $V$ twisted by these tautological classes, and prove that these intersection numbers are completely determined by the Gromov-Witten invariants of $V$. This results in families of Frobenius manifold structures on the cohomology ring of $V$ which includes the quantum cohomology as a spe…
We introduce a space of stable meromorphic differentials with poles of prescribed orders and define its tautological cohomology ring. This space, just as the space of holomorphic differentials, is stratified according to the set of multiplicities of zeros of the differential. The main goal of this paper is to compute the Poincaré-dual cohomology classes of all strata. We prove that all these classes are tautological and give an algorithm to compute them. In a second part of the paper we study the Picard group of the strata. We use the tools introduced in the first part to deduce several relati…
Tautological algebra of the moduli stack of semistable bundles of rank 2 on a general curve
研究一般曲线上的秩2稳定丛模堆栈的拟代数结构，揭示其由除子类生成的性质，扩展经典Porteous公式的应用。
The eleventh cohomology group of $\bar{\mathcal{M}}_{g,n}$
本文证明 $\bar{\mathcal{M}}_{g,n}$ 的第十一有理上同调群几乎总为零，并利用 $H^{11}(\bar{\mathcal{M}}_{1,11})$ 构造出具有非零奇上同调和非重言闭链类的新模空间例子。
We determine the Chow ring (with Q-coefficients) of M_6 by showing that all Chow classes are tautological. In particular, all algebraic cohomology is tautological, and the natural map from Chow to cohomology is injective. To demonstrate the utility of these methods, we also give quick derivations of the Chow groups of moduli spaces of curves of lower genus. The genus 6 case relies on the particularly beautiful Brill-Noether theory in this case, and in particular on a rank 5 vector bundle "relativizing" a baby case of a celebrated construction of Mukai, which we interpret as a subbundle of the …
We prove that the rational cohomology $H^i(\mathcal{T}_g;\mathbf{Q})$ of the moduli space of trigonal curves of genus $g$ is independent of $g$ in degree $i<\lfloor g/4\rfloor.$ This makes possible to define the stable cohomology ring as $H^\bullet(\mathcal{T}_g;\mathbf{Q})$ for a sufficiently large $g.$ We also compute the stable cohomology ring, which turns out to be isomorphic to the tautological ring. This is done by studying the embedding of trigonal curves in Hirzebruch surfaces and using Gorinov-Vassiliev's method.
In a series of two preprints, Y.-P. Lee studied relations satisfied by all formal Gromov-Witten potentials, as defined by A. Givental. He called them "universal relations" and studied their connection with tautological relations in the cohomology ring of moduli spaces of stable curves. Building on Y.-P. Lee's work, we give a simple proof of the fact that every tautological relation gives rise to a universal relation (which was also proved by Y.-P. Lee modulo certain results announced by C. Teleman). In particular, this implies that in any semi-simple Gromov-Witten theory where arbitrary correl…
The Gromov-Witten invariants of a smooth, projective variety $V$, when twisted by the tautological classes on the moduli space of stable maps, give rise to a family of cohomological field theories and endow the base of the family with coordinates. We prove that the potential functions associated to the tautological $ψ$ classes (the large phase space) and the $κ$ classes are related by a change of coordinates which generalizes a change of basis on the ring of symmetric functions. Our result is a generalization of the work of Manin--Zograf who studied the case where $V$ is a point. We utilize th…
We compute the cohomology spaces for the tautological bundle tensor the determinant bundle on the punctual Hilbert scheme H of subschemes of length n of a smooth projective surface X. We show that for L and A invertible vector bundles on X, and w the canonical bundle of X, if $w^{-1}\otimes L$, $w^{-1}\otimes A$ and A are ample vector bundles, then the higher cohomology spaces on H of the tautological bundle associated to L tensor the determinant bundle associated to A vanish, and the space of global sections is computed in terms of $H^0(A)$ and $H^0(L\otimes A)$. This result is motivated by t…
Witten's class on the moduli space of 3-spin curves defines a (non-semisimple) cohomological field theory. After a canonical modification, we construct an associated semisimple CohFT with a non-trivial vanishing property obtained from the homogeneity of Witten's class. Using the classification of semisimple CohFTs by Givental-Teleman, we derive two main results. The first is an explicit formula in the tautological ring of Mbar_{g,n} for Witten's class. The second, using the vanishing property, is the construction of relations in the tautological ring of Mbar_{g,n}. Pixton has previously conjec…
We compute some cohomology spaces for the symmetric power of the tautological bundle tensor the determinant bundle on the punctual Hilbert scheme of a complex smooth projective surface.
Independence of tautological classes and cohomological stability for strata of differentials
本文研究了微分分层的tautological环生成关系及上同调稳定性，证明了在特定条件下不存在低次关系，并推测在大g时tautological环非平凡。
Arithmetic volumes of moduli stacks of Shtukas
本文研究模堆栈中tautological classes的算术体积及其与Artin L函数导数的关系，并探讨phantom tautological ring的结构及其在函数域Colmez猜想中的应用。
In this work we compute the Chen--Ruan cohomology and the stringy Chow ring of the moduli spaces of smooth and stable $n$-pointed curves of genus 1. We suggest a definition for an Orbifold Tautological Ring in genus 1, which is both a subring of the Chen--Ruan cohomology and of the stringy Chow ring.
Hilbert polynomials of the first and second secant varieties
本文通过描述光滑射影复簇上2或3点的Hilbert方案上充分正线丛的对称幂的上同调群，将其维数用第一和第二割簇的希尔伯特多项式表示，并完全计算了这些多项式。
A Borel--Weil--Bott theorem for Quot schemes on $\mathbb{P}^1$
本文研究 $\mathbb{P}^1$ 上 Quot 概形中重言丛的上同调，建立了相应的 Borel–Weil–Bott 定理，并由此证明了 Marian、Oprea 和 Sam 关于重言丛外幂与对称幂的猜想。
Chow and cohomology rings of moduli stacks of plane quartics
本文研究了四次曲线模栈Hacking模栈的Chow环和上同调环，通过堆叠理论加权吹胀构造了一个光滑proper Deligne-Mumford堆栈，解决了KSBA和K-模空间之间的Calabi-Yau墙交叉问题，并计算了该模栈的Poincaré多项式，证明了循环类映射在有理系数下是同构的，并确定了其Chow环的生成元和关系。
We give a thorough study of Hurwitz stacks both in Galois and non galois case. The construction is applied to revisit somme classical examples, the stack of stable curves equipped with a level structure, and the stacks of tamely ramified cyclic covers. We exhibit some tautological cohomology classes, and give some universal relations between them. Applications are given to Cornalba-Harris type relations, and to some Hurwitz-Hodge integrals.
The fifteenth cohomology group of moduli spaces of stable curves
本研究针对稳定曲线模空间的第十五上同调群问题，利用半重言扩张新框架，证明了特定情形下的相关结论，确定了对应向量空间的关系与显式基，并给出了若干新小对的结果。
Hecke operators on symplectic surfaces and $χ$-independence
本文证明了关于拟射影辛曲面上单维层模空间的 BPS 上同调的 Toda χ-独立性猜想，并识别了与单维 Mukai 向量相关的 BPS Lie 代数，扩展了 Markman 的示性类生成定理。
We study the ring generated by the Chern classes of tautological line bundles on the moduli space of parabolic bundles of arbitrary rank on a Riemann surface. We show the Poincaré duals to these Chern classes have simple geometric representatives. We use this construction to show that the ring generated by these Chern classes vanishes below the dimension of the moduli space, in analogy with the Newstead-Ramanan conjecture for stable bundles.
In this paper, we give three bases for the cohomology groups of the Hilbert scheme of two points on projective space. Then, we use these bases to compute all effective and nef cones of higher codimensional cycles on the Hilbert scheme. Next, we compute the class in one of these bases of the Chern classes of tautological bundles coming from line bundles. Finally, we provide an application of these results to the degrees of secant varieties of complete intersections.
Cohomology rings of the moduli of one-dimensional sheaves on the projective plane
本文研究射影平面上半稳定一维层模栈的上同调环，利用几何重言关系与 Virasoro 算子确定至 5 次的环结构，并验证局部 P² 的精细 GV/PT 对应及加强 P=C 猜想。
We give a proof of Pixton's generalized Faber-Zagier relations in the tautological Chow ring of $\overline M_{g,n}$. The strategy is very similar to the work of Pandharipande-Pixton-Zvonkine, who have given a proof of the same result in cohomology. The main tool is the Givental-Teleman classification of semisimple cohomological field theories, which, while in general only known in cohomology, via virtual localization can be shown to be also valid in Chow for the equivariant Gromov-Witten theory of the projective line. We obtain the relations just from this theory.
Borel-Weil factorization for super Grassmannians
本文通过显式多线性操作构造超格雷厄姆 manifold 上施施尔 functors 的上同调，揭示其作为自由模的结构及不可约表示的性质。
Tautological relations and integrable systems
本文提出了一族关于带n个标记点的亏格g稳定代数曲线模空间上同调类的猜想关系，并证明这些关系蕴含与F-上同调场论相关的Dubrovin-Zhang和双分歧层次的基本性质，同时证明了n=1任意g及g=0任意n情形下的所有关系。
The Seidel maps are two maps associated to a Hamiltonian circle action on a convex symplectic manifold, one on Floer cohomology and one on quantum cohomology. We extend their definitions to $S^1$-equivariant Floer cohomology and $S^1$-equivariant quantum cohomology based on a construction of Maulik and Okounkov. The $S^1$-action used to construct $S^1$-equivariant Floer cohomology changes after applying the equivariant Seidel map (a similar phenomenon occurs for $S^1$-equivariant quantum cohomology). We show the equivariant Seidel map on $S^1$-equivariant quantum cohomology does not commute wi…
Let X be the quasi-projective symplectic surface that is given by the total space of the invertible sheaf O(-2) over the projective line. Let Hilb X be the family of Hilbert schemes of points on X. We give and prove a closed formula expressing any multiplicative characteristic class evaluated on the Hilb X in terms of the standard Fock space description of the cohomology of the Hilb X. As a side result, we also deduce a formula for the Chern character of the tangent bundles of the Hilb X. The results found here are another step towards a complete description of the tangent bundle of the Hilber…
This is the geometric part of two papers on the cohomology of Kaehler groups. Using non-Abelian Hodge theory we show that if a finitely presented group with an unbounded complex linear morphism is the fundamental group of a compact Kaehler manifold then its second or its fourth Betti number does not vanish. Combined with our first paper this shows that a cocompact lattice in a real simple Lie group G of sufficiently large real rank is Kaehler if and only if G is of Hermitian type (a conjecture of Carlson and Toledo).
We prove a new recursive relation between the correlators $< τ_{d_1}γ_1...τ_{d_n}γ_n >_{g,β}$, which together with known relations allows one to express all of them through the full system of Gromov-Witten invariants in the sense of Kontsevich-Manin and the intersection indices of tautological classes on $\bar{M}_{g,n}$, effectively calculable in view of earlier results due to Mumford, Kontsevich, Getzler, and Faber. This relation shows that a linear change of coordinates of the big phase space transforms the potential with gravitational descendants to another function defined completely in te…
This is the topological part of two papers on the cohomology of Kaehler groups. In this paper we show that if a linear duality group of dimension larger than 6 is the fundamental group of a compact Kaehler manifold then its second or its fourth Betti number is non-zero. As a corollary a cocompact p-adic lattice of rank larger than 6 is never Kaehler.
Topology of the Vakil--Zinger moduli space
本文研究了Vakil-Zinger构造的光滑一型映射空间的拓扑结构，推导其有理同调生成元并验证Hodge和Tate猜想，同时描述其Picard群并恢复奇同调消失结果。
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