Jean-Marc Couveignes, Emmanuel Hallouin
We show how to transport descent obstructions from the category of covers to the category of varieties. We deduce examples of curves having $\QQ$ as field of moduli, that admit models over every completion of $\QQ$, but have no model over $\QQ$.
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We extend the notion of rational points and cohomological obstructions on varieties to categories fibred in groupoids. We also establish the generalized theory of descent by torsors. Then we interpret the obstruction given by the second cohomology of abelian sheaves in terms of categorical points of gerbes, analogue to descent by torsors. As an application, we construct some composite obstructions not larger than the descent obstruction. We also propose some new kinds of obstructions including the derived obstruction, which has good behavior under a product and is also not larger than the desc…
Nous montrons comment associer à une gerbe définie sur un corps de nombres une obstruction de Brauer-Manin mesurant, comme dans le cas des variétés, le défaut d'existence d'une section globale. Ceci nous conduit à une généralisation de la dualité de Tate-Poitou au cas non-abélien. We find a way to associate to a gerbe defined over a number field a Brauer-Manin obstruction, which measures, as for varieties, the defect to the existence of a global section. This leads us to a generalization of Tate-Poitou duality in the non-abelian case.
Cohomological descent for obstructions to local-global principle
本文提出上同调降维框架，用于编码阿德里克点和局部-整体原理的障碍，通过构造新障碍获得某些代数叠类的障碍比较结果。
Rational points on varieties and the Brauer-Manin obstruction
本讲义介绍了有理点存在性的Brauer-Manin障碍，重点探讨理论与计算之间的相互作用。
We investigate the question of whether the existence of a family of local zero-cycles of degree $d$ orthogonal to the Brauer group implies the non-emptiness of the Brauer-Manin set for certain varieties. We provide various examples of Brauer-Manin obstruction to the existence of zero-cycles of appropriate degrees.
Recently Dasheng Wei proved that the Brauer-Manin obstruction is the only obstruction to the Hasse principle for 0-cycles of degree 1 on some fibrations over the projective line defined by bi-cyclic normic equations. In the present paper, we prove the exactness of the global-to-local sequence for Chow groups of 0-cycles of such varieties, which signifies that the Brauer-Manin obstruction is also the only obstruction to weak approximation for 0-cycles of arbitrary degree. Our main theorem also generalizes several existing results.
We study the section conjecture of anabelian geometry and the sufficiency of the finite descent obstruction to the Hasse principle for the moduli spaces of principally polarized abelian varieties and of curves over number fields. For the former we show that the section conjecture fails and the finite descent obstruction holds for a general class of adelic points, assuming several well-known conjectures. This is done by relating the problem to a local-global principle for Galois representations. For the latter, we prove some partial results that indicate that the finite descent obstruction suff…
A torsor under a k-group scheme G on a variety X over a number field k imposes a descent obstruction against the existence of rational points on X. We discuss the finite descent obstruction, that is for all such torsors under finite k-groups G, in view of a local-global interpolation property for sections of the fundamental group short exact sequence of X/k. There are applications to the Brauer-Manin obstruction, to the descent obstruction by torsors under linear groups, and to the birational version of Grothendieck's section conjecture over number fields. In particular, we obtain examples of …
We study the Brauer-Manin obstruction to the existence of zero-cycles of degree $d$ on certain classes of varieties over number fields. We generalise existing results in the literature and prove some results about fibrations over the projective line, where the geometric Brauer group of the generic fibre is not assumed to be finite. The idea is to assume that the Brauer-Manin obstruction to the Hasse principle is the only one for certain fibres and then deduce analogous results for zero-cycles.
This paper is devoted to the explicit description of the Galois descent obstruction for hyperelliptic curves of arbitrary genus whose reduced automorphism group is cyclic of order coprime to the characteristic of their ground field. Along the way, we obtain an arithmetic criterion for the existence of a hyperelliptic descent. The obstruction is described by the so-called arithmetic dihedral invariants of the curves in question. If it vanishes, then the use of these invariants also allows the explicit determination of a model over the field of moduli; if not, then one obtains a hyperelliptic mo…
We prove that for a large class of subvarieties of abelian varieties over global function fields, the Brauer-Manin condition on adelic points cuts out exactly the rational points. This result is obtained from more general results concerning the intersection of the adelic points of a subvariety with the adelic closure of the group of rational points of the abelian variety.
The local obstruction to semi-stable reduction for abelian varieties
本文综述了格罗滕迪克定义的阿贝尔簇半稳定约化局部障碍群的研究进展，并首次纳入等特征局部域情形，旨在给出仅依赖维数的群论刻画。
We provide a relation between Brauer-Manin obstruction and descent obstruction for torsors over open varieties under a connected linear algebraic group or a group of multiplicative type is given. Such a relation is further refined for torsors under a torus. As an appliaction, we prove that the semi-simple part of a connected linear algebraic group will satisfy strong approximation with Brauer-Manin obstruction if G iteself satisfies strong approximation with Brauer-Manin obstruction.The equivalence between descent obstruction and etale Brauer-Manin obstruction for smooth projective varieties i…
For smooth open toric varieties, we establish strong approximation off infinity with Brauer-Manin obstruction.
Rational points and Brauer--Manin obstruction on Shimura varieties of level one classifying abelian varieties with quaternionic multiplication
该研究探讨具有四元数乘法的阿贝尔簇对应的一级志村簇的有理点问题，证明这类志村簇极少存在有理点，为数论中志村簇有理点分布研究提供了结论。
Strong approximation with Brauer-Manin obstruction is established for smooth varieties containing a connected linear algebraic group with a compatible action.
Iterated descent obstructions for algebraic stacks
本文基于一个猜想证明了数域上光滑分离有限型叠的下降阻碍等于迭代下降阻碍，并将其推广到具有光滑几何整簇有限平展覆盖的代数叠。
Cohomological Obstructions for Varieties over $p$-adic Function Fields
本文引入 $p$-adic 函数域上光滑整簇的各种上同调障碍，证明非分歧障碍是算术对偶障碍中最精细的，并构造实例表明其优于 Manin 障碍，最后与非分歧障碍与下降障碍进行比较。
We extend the descent theory of Colliot-Thélène and Sansuc to arbitrary smooth algebraic varieties by removing the condition that every invertible regular function is constant. This links the Brauer--Manin obstruction for integral points on arithmetic schemes to the obstructions defined by torsors under groups of multiplicative type.
Reciprocity obstruction to strong approximation over p-adic function fields
本文在p进曲线函数域上构造SL_n齐性空间反例，证明强逼近失效，并提出且刻画了作为唯一障碍的互反障碍。
Let $k$ be a number field. In the spirit of a result by Yongqi Liang, we relate the arithmetic of rational points over finite extensions of $k$ to that of zero-cycles over $k$ for Kummer varieties over $k$. For example, for any Kummer variety $X$ over $k$, we show that if the Brauer-Manin obstruction is the only obstruction to the Hasse principle for rational points on $X$ over all finite extensions of $k$, then the ($2$-primary) Brauer-Manin obstruction is the only obstruction to the Hasse principle for zero-cycles of any given odd degree on $X$ over $k$. We also obtain similar results for pr…
Ramified descent
研究光滑几何连通簇X上的分枝下降问题，探讨数域K上的adele点如何近似于可提升到给定分枝覆盖的点，引入Brauer-Manin障碍，证明其对Hasse原理和弱近似构成障碍，且为阿贝尔覆盖提供非平凡超越障碍的例子。
Let $k$ be a number field, let $X$ be a Kummer variety over $k$, and let $δ$ be an odd integer. In the spirit of a result by Yongqi Liang, we relate the arithmetic of rational points over finite extensions of $k$ to that of zero-cycles over $k$ for $X$. For example, we show that if the Brauer-Manin obstruction is the only obstruction to the existence of rational points on $X$ over all finite extensions of $k$, then the $2$-primary Brauer-Manin obstruction is the only obstruction to the existence of a zero-cycle of degree $δ$ on $X$ over $k$.
Reflective obstructions of unitary modular varieties
本文利用 Prasad 体积公式定量估计酉模簇的反射障碍，证明高维时障碍足够小，并将其 Kodaira 维数问题归结为小权尖点形式构造。
We study the obstruction degrees of translates of sub-tori of multiplicative tori and we show how they are connected to lower bounds for the essential minimum of these varieties. In particular, we combine our computations with results of A. Schinzel and of F. Amoroso - R. Dvornicich, that we thus extend to translates of sub-tori defined over CM fields. This shows that the essential minimum of these varieties have a geometric behavior similar to that of varieties which are not translates of sub-tori. We also refine and extend to translates of sub-tori a lower bound obtained by D. Bertrand in co…
Comparing local-global obstructions on algebraic stacks
本文针对数域上的商叠，推广了簇的局部-整体障碍关系，证明Étale-Brauer障碍是多种相关障碍中最精细的一种，拓展了代数叠上局部-整体障碍的研究。
Let $k$ be a field of characteristic 0 and $G$ a linear algebraic $k$-group. When $G$ is abelian, it is well known that torsors under $G_{X}$ over a $k$-scheme $π:X\to \textup{Spec} k$ provide an obstruction to the existence of $k$-rational points on $X$, since Leray spectral sequence gives rise (when $X$ is 'nice', e.g. $X$ smooth and proper) to an exact sequence of groups (5-term exact sequence associated). This sequence gives an obstruction for a $\bar{G}_{X}$-torsor $\bar{P}\to\bar{X}$ with field of moduli $k$ to be defined over $k$, i.e. to be obtained by extension of scalars to the algeb…
Weak approximation of symmetric products and norm varieties
本文研究数域上簇的对称积及其光滑射影模型是否保持带Brauer-Manin障碍的弱逼近性质，并将同一方法推广到范数簇。
Brauer-Manin Obstruction on Generalized Kummer Varieties
本文研究数域上 Abel 簇经素数阶自同构取商所得广义 Kummer 簇，证明其 Brauer–Manin 障碍仅能源于 Brauer 群的 $p$-准素部分，并据此给出若干无局部–整体原理障碍的族。
Let r > 0 be an integer. We present a sufficient condition for an abelian variety A over a number field k to have infinitely many quadratic twists of rank at least r, in terms of density properties of rational points on the Kummer variety Km(A^r) of the r-fold product of A with itself. One consequence of our results is the following. Fix an abelian variety A over k, and suppose that for some r > 0 the Brauer-Manin obstruction to weak approximation on the Kummer variety Km(A^r) is the only one. Then A has a quadratic twist of rank at least r. Hence if the Brauer-Manin obstruction is the only on…
Faithfully flat descent of quasi-coherent complexes on rigid analytic varieties via condensed mathematics
本文通过凝聚数学将Mathew关于伪凝聚复形的忠实平坦下降结果推广至刚性解析簇上的拟凝聚复形。
Let $S$ be a finite set of primes. We prove that a form of finite Galois descent obstruction is the only obstruction to the existence of $\mathbb{Z}_{S}$-points on integral models of Hilbert modular varieties, extending a result of D.Helm and F.Voloch about modular curves. Let $L$ be a totally real field. Under (a special case of) the absolute Hodge conjecture and a weak Serre's conjecture for mod $\ell$ representations of the absolute Galois group of $L$, we prove that the same holds also for the $\mathcal{O}_{L,S}$-points.
Descent and étale-Brauer obstructions for 0-cycles
该研究定义了数域上代数簇0-闭链的下降集与平展-Brauer障碍集，证明其包含于Brauer-Manin集且与Suslin 0次奇异同调相容，将有理点算术研究工具迁移至0-闭链场景并推广Liang的策略到挠子，给出多类代数簇的应用。
For a family of varieties over a number field, we give conditions under which 100% of members have no Brauer-Manin obstruction to the Hasse principle.
Refined obstructions to local-global principles for 0-cycles
本文引入新的精细化障碍，用于研究数字段上代数簇0-循环的局部-全局原理，通过Tate-Shafarevich群的有限性，探讨广义Kummer簇和双椭圆面的Hasse原理和弱逼近，并回答Zhang关于Brauer-Manin和连通降阶障碍关系的问题。
We introduce a new obstruction to lifting smooth proper varieties in characteristic $p>0$ to characteristic $0$. It is based on Grothendieck's specialization homomorphism and the resulting discrete finiteness properties of étale fundamental groups.
Suppose $X$ is a torsor under an abelian variety $A$ over a number field. We show that any adelic point of $X$ that is orthogonal to the algebraic Brauer group of $X$ is orthogonal to the whole Brauer group of $X$. We also show that if there is a Brauer-Manin obstruction to the existence of rational points on $X$, then there is already an obstruction coming from the locally constant Brauer classes. These results had previously been established under the assumption that $A$ has finite Tate-Shafarevich group. Our results are unconditional.
Let k be a number field and X a smooth projective k-variety. In this paper, we study the information obtainable from descent via torsors under finite k-group schemes on the location of the k-rational points on X within the adelic points. Our main result is that if a curve C/k maps nontrivially into an abelian variety A/k such that A(k) is finite and Sha(k,A) has no nontrivial divisible elements, then the information coming from finite abelian descent cuts out precisely the rational points of C. We conjecture that this is the case for all curves of genus at least 2. We relate finite descent obs…
Let $\mathbb{F}$ be a finite field and $C,D$ smooth, geometrically irreducible proper curves over $\mathbb{F}$ and set $K = \mathbb{F}(D)$. We consider Brauer-Manin and abelian descent obstructions to the existence of rational points and to weak approximation for the curve $C \otimes_\mathbb{F} K$. In particular, we show that Brauer-Manin is the only obstruction to weak approximation and the Hasse principle in the case that the genus of $D$ is less than that of $C$. We also show that we can identify the points corresponding to non-constant maps $D \to C$ using Frobenius descents.
Let X be a smooth variety over a number field k embedded as a degree d subvariety of $\mathbb{P}^n$ and suppose that X is a counterexample to the Hasse principle explained by the Brauer-Manin obstruction. We consider the question of whether the obstruction is given by the d-primary subgroup of the Brauer group, which would have both theoretic and algorithmic implications. We prove that this question has a positive answer in the case of torsors under abelian varieties, Kummer surfaces and (conditional on finiteness of Tate-Shafarevich groups) bielliptic surfaces. For Kummer varieties we show th…
Etale descent obstruction and anabelian geometry of curves over finite fields
本文通过建立平展基本群之间的态射与全局函数域上曲线的局部常值阿代尔点之间的双射，将Grothendieck的阿纳贝尔猜想与Sutherland和第二个作者的最新猜想联系起来，为阿纳贝尔猜想提供了进一步证据。
For a nice algebraic variety $X$ over a number field $F$, one of the central problems of Diophantine Geometry is to locate precisely the set $X(F)$ inside $X(\A_F)$, where $\A_F$ denotes the ring of adèles of $F$. One approach to this problem is provided by the finite descent obstruction, which is defined to be the set of adelic points which can be lifted to twists of torsors for (certain) finite étale group schemes over $F$ on $X$. More recently, Kim proposed an iterative construction of another subset of $X(\A_F)$ which contains the set of rational points. In this paper, we compare the two c…
The Brauer-Manin obstruction on algebraic stacks
本文研究代数堆上的Brauer-Manin集和配对，扩展了Colliot-Thélène和Sansuc的降理论，证明了局部由变分线性群商的堆的Brauer群的 torsion 性，并展示了Brauer-Manin障碍与其它上同调障碍的一致性。
Let $X$ be a rationally connected algebraic variety, defined over a number field $k$. We find a relation between the arithmetic of rational points on $X$ and the arithmetic of zero-cycles. More precisely, we consider the following statements: (1) the Brauer-Manin obstruction is the only obstruction to weak approximation for $K$-rational points on $X_K$ for all finite extensions $K/k$; (2) the Brauer-Manin obstruction is the only obstruction to weak approximation in some sense that we define for zero-cycles of degree 1 on $X_K$ for all finite extensions $K/k$; (3) a certain sequence of local-gl…
We give large families of Shimura curves defined by congruence conditions, all of whose twists lack $p$-adic points for some $p$. For each such curve we give analytically large families of counterexamples to the Hasse principle via the descent (or equivalently étale Brauer-Manin) obstruction to rational points applied to étale coverings coming from the level structure. More precisely, we find infinitely many quadratic fields defined using congruence conditions such that a twist of a related Shimura curve by each of those fields violates the Hasse principle. As a minimal example, we find the tw…
We reinterpret Kim's non-abelian reciprocity maps for algebraic varieties as obstruction towers of mapping spaces of etale homotopy types, removing technical hypotheses such as global basepoints and cohomological constraints. We then extend the theory by considering alternative natural series of extensions, one of which gives an obstruction tower whose first stage is the Brauer--Manin obstruction, allowing us to determine when Kim's maps recover the Brauer-Manin locus. A tower based on relative completions yields non-trivial reciprocity maps even for Shimura varieties; for the stacky modular c…
Weak approximation versus the Hasse principle for subvarieties of abelian varieties
本文研究阿贝尔簇子簇的弱逼近失效问题，证明了有限下降作为有理点存在的唯一障碍可推导出弱逼近失效由有限下降解释，并推广至 Mordell-Weil 筛障碍。
Galois invariants of finite abelian descent and Brauer sets
该文研究全局域上代数簇的有限阿贝尔下降、Brauer-Manin障碍对应的阿德尔点子集的伽罗瓦不变量还原基域障碍集的条件，并将常曲线的相关结果推广到函数域上的等平凡曲线。
We introduce descent methods to the study of strong approximation on algebraic varieties. We apply them to two classes of varieties defined by P(t)=N_{K/k}(z): firstly for quartic extensions of number fields K/k and quadratic polynomials P(t) in one variable, and secondly for k=Q, an arbitrary number field K and P(t) a product of linear polynomials over Q in at least two variables. Finally, we illustrate that a certain unboundedness condition at archimedean places is necessary for strong approximation.
We consider local-global principles for rational points on varieties, in particular torsors, over one-variable function fields over complete discretely valued fields. There are several notions of such principles, arising either from the valuation theory of the function field, or from the geometry of a regular model of the function field. Our results compare the corresponding obstructions, proving in particular that a local-global principle with respect to valuations implies a local-global principle with respect to a sufficiently fine regular model.
We show that a positive proportion of cubic fields are not monogenic, despite having no local obstruction to being monogenic. Our proof involves the comparison of $2$-descent and $3$-descent in a certain family of Mordell curves $E_k \colon y^2 = x^3 + k$. As a by-product of our methods, we show that, for every $r \geq 0$, a positive proportion of curves $E_k$ have Tate--Shafarevich group with $3$-rank at least $r$.
We study probability distributions arising from local obstructions to the existence of $p$-adic points in families of varieties. In certain cases we show that an Erdős-Kac type law holds.
The Brauer-Manin obstruction is used to explain the failure of the local-global principle for algebraic varieties. In 1999 Skorobogatov gave the first example of a variety that does not satisfy the local-global principle which is not explained by the Brauer-Manin obstruction. He did so by applying the Brauer-Manin obstruction to étale covers of the variety, and thus defining a finer obstruction. In 2008 Poonen gave the first example of failure of the local-global principle which cannot be explained for by Skorobogatov's étale-Brauer obstruction. However, Poonen's construction was not accompani…
Geometrically Abelian Sections on Higher-Dimensional Varieties
该研究探讨高维簇的算术信息检测，通过几何阿贝尔基本群截面，在p进域、有限生成域上推导相关结论，还给出Esnault与Wittenberg定理强化版本的新证明。
Solvable Descent and the Grunwald Problem for Solvable Groups
本文通过Harpaz和Wittenberg的方法证明了可解下降定理，解决了可解群的Grünwald问题，并提供了Shafarevich逆伽罗瓦问题的替代证明。
Inspired by Kummer theory on abelian varieties, we give similar looking descriptions of the Galois groups occuring in the differential Galois theories of Picard-Vessiot, Kolchin and Pillay, and mention some arithmetic applications.
Tori and surfaces violating a local-to-global principle for rationality
本文证明了Brauer-Manin障碍即使在基变换不变形式下也不足以解释有理性的局部到全局原理的反例，并给出了全局域上环面簇和有理曲面的具体例子。
In 2010, Poonen gave the first example of failure of the local-global principle that cannot be explained by Skorobogatov's étale Brauer-Manin obstruction. Motivated by this example, we show that the Brauer-Manin obstruction detects non-existence of rational points on a sufficiently fine Zariski open cover of any variety over an imaginary quadratic or totally real field. We provide some evidence for why this is expected to happen more generally over any number field, some of which relates to the section conjecture in anabelian geometry. We then prove a result about the behavior of the étale Bra…
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…
We split the program of explicit descent of elliptic curves into two parts. For $n=3$ and $n=5,$ we first display a model for the universal elliptic curve $E$ with full level $n$ structure and describe the map of rational points of $E$ to the cohomology group $H^1(G, E[n]).$ Second, we find models in $\PP^{n-1}$ of principal homogeneous spaces of $E$ corresponding to all possible elements of $H^1(G, E[n]),$ i.e. for those elements with trivial period-index obstruction. For this we use the relationship established in \cite{me2} between the period-index obstruction and the norm symbol, a general…
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