Ido Efrat, Eliyahu Matzri
Let p be a prime number and F a field containing a root of unity of order p. We relate recent results on vanishing of triple Massey products in the mod-p Galois cohomology of F, due to Hopkins, Wickelgren, Minac, and Tan, to classical results in the theory of central simple algebras. For global fields, we prove a stronger form of the vanishing property.
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We prove the Massey Vanishing Conjecture for $n=4$ and $p=2$. That is, we show that for all fields $F$, if a fourfold Massey product modulo $2$ is defined over $F$, then it vanishes over $F$.
A major difficult problem in Galois theory is the characterization of profinite groups which are realizable as absolute Galois groups of fields. Recently the Kernel $n$-Unipotent Conjecture and the Vanishing $n$-Massey Conjecture for $n\geq 3$ were formulated. These conjectures evolved in the last forty years as a byproduct of the application of topological methods to Galois cohomology. We show that both of these conjectures are true for odd rigid fields. This is the first case of a significant family of fields where both of the conjectures are verified besides fields whose Galois groups of $p…
A conjecture of Mináč and Tân predicts that for any n>2, any prime p and any field k, the Massey product of n Galois cohomology classes in H^1(k,Z/pZ) must vanish if it is defined. We establish this conjecture when k is a number field.
We show that the absolute Galois group of any field has the vanishing triple Massey product property. Several corollaries for the structure of maximal pro-$p$-quotient of absolute Galois groups are deduced. Furthermore, the vanishing of some higher Massey products is proved.
Massey products and unipotent extensions with restricted ramification
本文构造了具有限制分歧和分裂的数域pro-p扩张新例子，其伽罗瓦群分解为局部域pro-p绝对伽罗瓦群的余积，并证明这些扩张满足强Massey消失性质，从而具有大的单幂商。
Massey products in Galois cohomology and the Elementary Type Conjecture
本文证明Efrat初等类型猜想蕴含Minač--Tân Massey消失猜想的强化版，从而在若干情形下使含单位根的域的极大pro-p伽罗瓦群满足强n-Massey消失性质。
We study the vanishing of four-fold Massey products in mod p Galois cohomology. First, we describe a sufficient condition, which is simply expressed by the vanishing of some cup-products, in direct analogy with the work of Guillot, Mináč and Topaz for p=2. For local fields with enough roots of unity, we prove that this sufficient condition is also necessary, and we ask whether this is a general fact. We provide a simple splitting variety, that is, a variety which has a rational point if and only if our sufficient condition is satisfied. It has rational points over local fields, and so, if it s…
Massey products in Galois cohomology and Pythagorean fields
本文证明Minac-Tan的Massey消没猜想的加强版本对极大pro-2伽罗瓦群为初等型且平方类有限的域成立，从而涵盖有限平方类数的毕达哥拉斯域及其有限扩张。
Massey products and the Iwasawa theory of fine Selmer groups
本文用Massey积重新表述Coates-Sujatha猜想，证明μ-不变量的消失可传递至邻域扩张，并建立形变环无阻碍性与精细Selmer群μ-不变量消失的等价关系。
On the Vanishing of the Brauer-Manin Obstruction for Normic Bundles
研究有限域扩张下布劳尔 - 马宁障碍对有理点存在性的影响，针对数域上\((p, mp)\)-范数丛，证明基变换到特定有限扩张后障碍消失，对\((p,2p)\)-范数丛给出更简便条件，且证明可除性假设通常最优。
On the Massey Vanishing Conjecture and Formal Hilbert 90
本文在满足形式希尔伯特定理90的投射有限群与连续特征的设定下，证明了三重及部分退化四重Massey积的Massey消没猜想，核心是构造了对应希尔伯特90模。
Brauer--Manin obstruction from failure of Kodaira vanishing in positive characteristic
研究正特征全局域上 Kodaira 消失定理失效的光滑射影曲面的 Brauer-Manin 集，特别应用于 Raynaud 曲面。
Let p be a prime. We study pro-p groups of p-absolute Galois type, as defined by Lam-Liu-Sharifi-Wake-Wang. We prove that the pro-p completion of the right-angled Artin group associated to a chordal simplicial graph is of p-absolute Galois type, and moreover it satisfies a strong version of the Massey vanishing property. Also, we prove that Demushkin groups are of p-absolute Galois type, and that the free pro-p product -- and, under certain conditions, the direct product -- of two pro-p groups of p-absolute Galois type satisfying the Massey vanishing property is again a pro-p group of p-absolu…
We explicitly construct a del Pezzo surface $X$ of degree 4 over a field $k$ such that $\operatorname{H}^1(k,\operatorname{Pic}\overline X)$ is isomorphic to $\mathbb{ZZ}/2\mathbb{Z}$ while $\operatorname{Br} X/\operatorname{Br} k$ is trivial. This proves that the algorithm to compute the Brauer group in [VAV] cannot be generalized in some cases.
Vanishing of Brauer classes on K3 surfaces under reduction
本文证明了数域上K3曲面的Brauer类在某些技术假设下存在无穷多个约化使其消失，回答了Frei--Hassett--Várilly-Alvarado的问题。
We show that any triple Massey product with respect to prime 2 contains 0 whenever it is defined over any field. This extends the theorem of M. J. Hopkins and K. G. Wickelgren, from global fields to any fields. This is the first time when the vanishing of any $n$-Massey product for some prime $p$ has been established for all fields. This leads to a strong restriction on the shape of relations in the maximal pro-2-quotients of absolute Galois groups, which was out of reach until now. We also develop an extension of Serre's transgression method to detect triple commutators in relations of pro-$p…
Massey products in the étale cohomology of number fields
本文研究了数字段整环的étale上同调中3重Massey乘积的公式，发现虚二次域的类群具有无限p-类域塔的例子，并推翻了McLeman的(3,3)猜想。
Triple Massey products for higher genus curves
针对数域上绝对不可约光滑射影曲线，本文构造各亏格 $g>1$ 与素数 $\ell>3$ 下的超椭圆曲线，证明存在不含 $0$ 的非空 $\mathbb{Z}/\ell$ 系数三重 Massey 积。
In this paper, we develop a new necessary and sufficient condition for the vanishing of 4-Massey products of elements in the mod-2 Galois cohomology of a field. This new description allows us to define a splitting variety for 4-Massey products, which is shown in the Appendix to satisfy a local-to-global principle over number fields. As a consequence, we prove that, for a number field, all such 4-Massey products vanish whenever they are defined. This provides new explicit restrictions on the structure of absolute Galois groups of number fields.
Massey products and elliptic curves
本文研究完美域上绝对不可约光滑射影曲线中系数为 $\mathbb{Z}/\ell$ 的高阶 Massey 积消失问题，并完整刻画椭圆曲线上三重 Massey 积非消失的条件。
Let X be a homogeneous space of a quasi-trivial k-group G, with geometric stabilizer H, over a number field k. We prove that under certain conditions on the character group of H, certain algebraic Brauer-Manin obstructions to the Hasse principle and weak approximation vanish, because the abelian groups where they take values vanish. When H is connected or abelian, these algebraic Brauer-Manin obstructions to the Hasse principle and weak approximation are the only ones, so we prove the Hasse principle and weak approximation for X under certain conditions. As an application, we obtain new suffic…
Let $k$ be a finite field, a $p$-adic field or a number field. Let $K$ be a finite extension of the Laurent series field in $m$ variables $k((x_1,...,x_m))$ or, more generally, a finite extension of the field of rational functions $k((x_1,...,x_m))(y_1,...,y_n)$. When $r$ is an integer, we consider the Galois module $\mathbb{Q}/\mathbb{Z}(r)$ over $K$ and we prove several vanishing theorems for its cohomology. In the particular case when $K$ is a finite extension of the Laurent series field in two variables $k((x_1,x_2))$, we also prove exact sequences that play the role of the Brauer-Hasse-No…
We provide an explicit algorithm to compute a Massey triple product relative to a defining system for a smooth projective plane curve $X$ defined by a homogeneous polynomial $G(\underline x)$ over a field. The main idea is to use the description (due to Carlson and Griffiths) of the cup product for $H^1(X,\mathbb{C})$ in terms of the multiplications inside the Jacobian ring of $G(\underline x)$ and the Cech-deRham complex of $X$. Our algorithm gives a criterion whether a Massey triple product vanishes or not in $H^2(X)$ under a particular non-trivial defining system of the Massey triple produc…
Given a profinite group G of finite p-cohomological dimension and a pro-p quotient H of G by a closed normal subgroup N, we study the filtration on the Iwasawa cohomology of N by powers of the augmentation ideal in the group algebra of H. We show that the graded pieces are related to the cohomology of G via analogues of Bockstein maps for the powers of the augmentation ideal. For certain groups H, we relate the values of these generalized Bockstein maps to Massey products relative to a restricted class of defining systems depending on H. We apply our study to prove lower bounds on the p-ranks …
We relate the Brauer group of a smooth variety over a p-adic field to the geometry of the special fibre of a regular model, using the purity theorem in étale cohomology. As an illustration, we describe how the Brauer group of a smooth del Pezzo surface is determined by the singularity type of its reduction. We then relate the evaluation of an element of the Brauer group to the existence of points on certain torsors over the special fibre; we use this to describe situations when the evaluation is constant, and situations when the evaluation is surjective. In the latter case, we describe how thi…
Let F be a finite field and l a prime not equal to the characteristic of F. Let K be the function field of a surface over F. Assume that K contains a primitive lth root of unity. In the paper we prove a certain local-global principle for elements of H^3(K, μ_l) in terms of symbols in H^2(K, μ_l) with respect to discrete valuations of K. We also show that this local global principle is equivalent to the vanishing of certain unramified cohomology groups of 3-folds over finite fields. Using this local-global principle we show that every element in H^3(F, μ_l) is a symbol. The vanishing of the unr…
Non-formality of Galois cohomology modulo all primes
本文证明了存在域扩张使得素数$p$处的强Massey消没猜想不成立，其绝对Galois群的上链微分分次环非形式，从而回答了Positselski的问题。
Weak and genuine A_n-formality for number fields
该研究引入伽罗瓦上链代数的弱A_n-形式性，刻画有限群的A_n-形式性，证明数域在特定素数条件下有限A_3-嵌入问题可解但无相容解族，揭示真正A_3-形式性可检测全局相容性阻碍。
Let $G$ be a finite group acting on the rational function field $\mathbb{C}(x_g : g\in G)$ by $\mathbb{C}$-automorphisms $h(x_g)=x_{hg}$ for any $g,h\in G$. Noether's problem asks whether the invariant field $\mathbb{C}(G)=k(x_g : g\in G)^G$ is rational (i.e. purely transcendental) over $\mathbb{C}$. Saltman and Bogomolov, respectively, showed that for any prime $p$ there exist groups $G$ of order $p^9$ and of order $p^6$ such that $\mathbb{C}(G)$ is not rational over $\mathbb{C}$ by showing the non-vanishing of the unramified Brauer group: $Br_{nr}(\mathbb{C}(G))\neq 0$. For $p=2$, Chu, Hu, K…
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