Donald Yau
Boardman, Johnson, and Wilson gave a precise formulation for an unstable algebra over a generalized cohomology theory. Modifying their definition slightly in the case of complex K-theory by taking into account its periodicity, we prove that an unstable algebra for complex $K$-theory is precisely a filtered $λ$-ring, and vice versa.
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Motivated by recent works on the genus of classifying spaces of compact Lie groups, here we study the set of filtered $λ$-ring structures over a filtered ring from a purely algebraic point of view. From a global perspective, we first show that this set has a canonical topology compatible with the filtration on the given filtered ring. For power series rings $R \llbrack x \rrbrack$, where $R$ is between $\bZ$ and $\bQ$, with the $x$-adic filtration, we mimic the construction of the Lazard ring in formal group theory and show that the set of filtered $λ$-ring structures over $R \llbrack x \rrbra…
Filtrations and cohomology I: crystallization
本文比较了多种滤过导出交换环的概念，探讨了HKR-滤过Hochschild同调与Hodge-滤过上同调，并证明de Rham上同调是无穷小上同调的结晶化。
We construct Hodge filtered function spaces associated to infinite loop spaces. For Brown-Peterson cohomology, we show that the corresponding Hodge filtered spaces satisfy an analog of Wilson's unstable splitting. As a consequence, we obtain an analog of Quillen's theorem for Hodge filtered Brown-Peterson cohomology for complex manifolds.
A Bott tower is an iterated $\CP ^1$-bundle over a point, where each $\CP ^1$-bundle is the projectivization of a rank $2$ decomposable complex vector bundle. For a Bott tower, the filtered cohomology is naturally defined. We show that isomorphism classes of Bott towers are distinguished by their filtered cohomology rings. We even show that any filtered cohomology ring isomorphism between two Bott towers is induced by an isomorphism of the Bott towers.
A cohomology theory for lambda-rings is developed. This is then applied to study deformations of lambda-rings.
It is shown that most possibly truncated power series rings admit uncountably many filtered lambda-ring structures. The question of how many of these filtered lambda-ring structures are topologically realizable by the K-theory of torsionfree spaces is also considered for truncated polynomial rings.
We construct Hodge filtered cohomology groups for complex manifolds that combine the topological information of generalized cohomology theories with geometric data of Hodge filtered holomorphic forms. This theory provides a natural generalization of Deligne cohomology. For smooth complex algebraic varieties, we show that the theory satisfies a projective bundle formula and $\A^1$-homotopy invariance. Moreover, we obtain transfer maps along projective morphisms.
Motivated by the cohomology theory of loop spaces, we consider a special class of higher order homotopy commutative differential graded algebras and construct the filtered Hirsch model for such an algebra $A$. When $x\in H(A)$ with $\mathbb{Z}$ coefficients and $x^{2}=0,$ the symmetric Massey products $% \langle x\rangle ^{n}$ with $n\geq 3$ have a finite order (whenever defined). However, if $\Bbbk $ is a field of characteristic zero, $\langle x\rangle ^{n}$ is defined and vanishes in $H(A\otimes \Bbbk )$ for all $n$. If $p$ is an odd prime, the Kraines formula $\langle x\rangle ^{p}=-β\mathc…
Let X be a pseudomanifold. In this text, we use a simplicial blow-up to define a cochain complex whose cohomology with coefficients in a field, is isomorphic to the intersection cohomology of X, introduced by M. Goresky and R. MacPherson. We do it simplicially in the setting of a filtered version of face sets, also called simplicial sets without degeneracies, in the sense of C.P. Rourke and B.J. Sanderson. We define perverse local systems over filtered face sets and intersection cohomology with coefficients in a perverse local system. In particular, as announced above when X is a pseudomanifol…
The action of Sq on the cohomology of the Steenrod algebra is induced by an endomorphism Theta of the Lambda algebra. This paper studies the behavior of Theta in order to understand the action of Sq; the main result is that Sq is injective in filtrations less than 4, and its kernel on the 4-line is computed.
Recovering generalized homology from Floer homology: the complex oriented case
本文通过完备Tate上同调将滤过圆等变谱与复定向上同调理论关联，证明对Liouville流形仅依赖稳定同伦型，并利用Morava K-理论及复K-理论计算恢复整数同调与复K-理论。
We discuss an Abel-Jacobi invariant for algebraic cobordism cycles whose image in topological cobordism vanishes. The existence of this invariant follows by abstract arguments from the construction of Hodge filtered cohomology theories in joint work of Michael J. Hopkins and the author. In this paper, we give a concrete description of the new Abel-Jacobi map and Hodge filtered cohomology groups for projective smooth complex varieties.
Sufficient conditions on a space are given which guarantee that the $K$-theory ring and the ordinary cohomology ring with coefficients over a principal ideal domain are invariants of, respectively, the adic genus and the SNT set. An independent proof of Notbohm's theorem on the classification of the adic genus of $BS^3$ by $KO$-theory $λ$-rings is given. An immediate consequence of these results about adic genus is that the power series ring $\mathbf{Z} \lbrack \lbrack x \rbrack \rbrack$ admits uncountably many pairwise non-isomorphic $λ$-ring structures.
Filtered complexes and cohomologically equivalent subcomplexes
受Rumin工作启发，提出从任意有限深度滤过余链复形构造上同调等价子复形的通用方法，证明其仅依赖滤过本身，并揭示与谱序列的联系。
Writing $\mathbb A$ for the 2-primary Steenrod algebra, which is the algebra of stable natural endomorphisms of the mod 2 cohomology functor on topological spaces. Working at the prime 2, computing the cohomology of $\mathbb A$ is an important problem of Algebraic topology, because it is the initial page of the Adams spectral sequence converging to stable homotopy groups of the spheres. A relatively efficient tool to describe this cohomology is the Singer algebraic transfer of rank $n$ in [Math. Z. 202 (1989), 493-523], which passes from a certain subquotient of a divided power algebra to the …
We prove a Verdier Hypercovering Theorem for cohomology theories arising from motivic spectra. This allows us to construct for smooth quasi-projective complex varieties a natural morphism from etale algebraic to Hodge filtered complex cobordism, which extends the map from etale motivic to Deligne-Beilinson cohomology.
An old result of the first author and David Lieberman says that if a compact Kaehler manifold X admits a holomorphic vector field V having at least one zero, then the Dolbeault cohomology algebra H^*(X, Ω^*) of X is isomorphic with the bigraded algebra associated to a certain filtered graded ring. If V has isolated zeros this is the graded algebra associated to a certain filtration of the coordinate ring of the scheme Z defined by zero(V). The purpose of this note is to show that if V is generated by a torus action then equivariant Dolbeault cohomology can be used to give direct geometric proo…
A filtered Hochschild-Kostant-Rosenberg theorem for real Hochschild homology
本文在$ C_2 $-Mackey函子中引入导出对合代数，证明其实Hochschild同调存在滤过且相关分次等同对合de Rham复形，并特化为Raksit的HKR-滤过Hochschild同调。
The algebra S of symmetric invariants over the field with two elements is an unstable algebra over the Steenrod algebra A, and is isomorphic to the mod two cohomology of BO, the classifying space for vector bundles. We provide a minimal presentation for S in the category of unstable A-algebras, i.e., minimal generators and minimal relations. From this we produce minimal presentations for various unstable A-algebras associated with the cohomology of related spaces, such as the BO(2^m-1) that classify finite dimensional vector bundles, and the connected covers of BO. The presentations then show …
We show how to induce products in sheaf cohomology for a wide variety of coefficients: sheaves of dg commutative and Lie algebras, symmetric Omega-spectra, filtered dg algebras, operads and operad algebras.
De Rham affineness of the Nygaard filtered prismatization in positive characteristic
本文研究了Nygaard filtered prismatization在正特征下的de Rham affineness性质，并通过公理化方法探讨其与相对de Rham stack的关系。
We identify the equivariant structure of the filtered pieces of the motivic filtration defined by Bhatt, Morrow and Scholze on the topological Hochschild cohomology spectrum of polynomial algebras over $\mathbb{F}_p$.
$q$-de Rham cohomology and topological Hochschild homology over ku
本文证明：若环 $R$ 有球面 $\mathbb{E}_2$-提升，则 $\mathrm{TC}^-$ 的偶滤过分次分量给出 $q$-de Rham 上同调上的 $q$-形变 Hodge 滤过，并由此构造数域 Habiro 环。
Hopf algebras in the cohomology of $\mathcal{A}_g$, $\mathrm{GL}_n(\mathbb{Z})$, and $\mathrm{SL}_n(\mathbb{Z})$
本文在主极化阿贝尔簇模空间的权零紧支上同调上构造了双分次余交换Hopf代数结构，利用Waldhausen构造的滤过变体证明Quillen谱序列是Hopf代数谱序列，并推导出相关上同调群维数随参数呈指数级增长。
Hochschild cohomology and extensions of triangulated categories
本文定义增强三角范畴的一阶范畴形变，证明其与 HH² 类一一对应，并用于解释 dg 代数弯曲形变及构造经典导出范畴的范畴解消。
Let X and Y be finite-type CW-complexes (X connected, Y simply connected), such that the rational cohomology ring of Y is a k-rescaling of the rational cohomology ring of X. Assume H^*(X,Q) is a Koszul algebra. Then, the homotopy Lie algebra pi_*(Omega Y) tensor Q equals, up to k-rescaling, the graded rational Lie algebra associated to the lower central series of pi_1(X). If Y is a formal space, this equality is actually equivalent to the Koszulness of H^*(X,Q). If X is formal (and only then), the equality lifts to a filtered isomorphism between the Malcev completion of pi_1(X) and the complet…
André-Quillen cohomology in the context of curved algebras
本文针对弯曲代数中拟同构失效的问题，通过引入不一定是augment的operad及滤过完全模上的预微分构造弯曲代数的同伦理论，结合Bar、cobar与Koszul对偶理论，实现了同伦弯曲代数的显式化，并揭示了其与导出复解析几何的联系。
Let $F_2$ be the prime field of two elements and let $GL_s:= GL(s, F_2)$ be the general linear group of rank $s.$ Denote by $\mathscr A$ the Steenrod algebra over $F_2.$ The (mod-2) Lambda algebra, $Λ,$ is one of the tools to describe those mysterious "Ext-groups". In addition, the $s$-th algebraic transfer of William Singer \cite{Singer} is also expected to be a useful tool in the study of them. This transfer is a homomorphism $Tr_s: F_2 \otimes_{GL_s}P_{\mathscr A}(H_{*}(B\mathbb V_s, F_2))\to {\rm Ext}_{\mathscr {A}}^{s,s+*}(F_2, F_2),$ where $\mathbb V_s$ denotes the elementary abelian $2$…
On the Goldman-Millson theorem for $A_\infty$-algebras in arbitrary characteristic
本文研究完备滤过 $A_\infty$-代数的形变理论，证明任意特征下的 Goldman–Millson 定理，刻画神经的同伦群，并在特征零下建立其与交换子 $L_\infty$-代数 Maurer–Cartan 集的同伦等价。
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