In this note we answer two question posed by Berkani and Koliha [Acta Sci. Math.69 (2003), 359–376]. We show that generalized Browder's (resp. generalized $a$-Browder's) theorem holds for a Banach space operator if and only if Browder's (resp. $a$-Browder's) theorem does. We also give condition under which generalized Weyl's (resp. generalized $a$-Weyl's) theorem is equivalent to Weyl's (resp. $a$-Weyl's) theorem.

In this paper, we prove that, for any integer $n\ge 2,$ and any $\delta > 0$ there exists an $\epsilon(n,\delta) \ge 0$ such that if $M$ is an $n$-dimensional complete manifold with sectional curvature $K_M \ge 1$ and if $M$ has conjugate radius $\rho \ge\frac{\pi}{2}+\delta $ and contains a geodesic loop of length $2(\pi-\epsilon(n,\delta))$ then $M$ is diffeomorphic to the Euclidian unit sphere $\mathbb{S}^{n}.$

We prove that Mazur's functional characterization for one-sided estimates can be restricted to smaller classes of functionals in the case in which the functions under consideration are continuous. We apply this result to stability problems for dynamical systems in $l^\infty$, and in the Banach space of all selfadjoint operators on a Hilbert space.

For a closed topological $n$-manifold $X$, the surgery exact sequence contains the set of manifold structures and the set of tangential structures of $X$. In the case of a compact topological $n$-manifold with boundary $(X$, $\partial X)$, the classical surgery theory usually considers two different types of structures. The first one concerns structures whose restrictions are fixed on the boundary. The second one uses two similar structures on the manifold pair. In his classical book, Wall mentioned the possibility of introducing a mixed type of structure on a manifold with boundary. Following this suggestion, we introduce mixed structures on a topological manifold with boundary, and describe their properties. Then we obtain connections between these structures and the classical ones, and prove that they fit in some surgery exact sequences. The relationships can be described by using certain braids of exact sequences. Finally, we discuss explicitly several geometric examples.

In this paper we present some results about $wV$ (weak property $V$ of Peł czyński) or property $wV^*$ (weak property $V^*$ of Peł czyński) in Banach spaces. We show that $E$ has property $wV$ if for any reflexive subspace $F$ of $E^*$, $^{\perp} {F}$ has property $wV$. It is shown that $G$ has property $wV$ if under some condition $K_{w^*}(E^*, F^*)$ contains the dual of $G$. Moreover, it is proved that $E^*$ contains a copy of $c_0$ if and only if $E$ contains a copy of $\ell_1$ where $E$ has property $wV^*$. Finally, the identity between $L(C(\Omega, E), F)$ and $WP(C(\Omega, E), F)$ is investigated.

It is proved that every abelian VNL-ring is an SVNL-ring, which gives a positive answer to a question of Osba et al. [7]. Some characterizations of duo VNL-rings are given and some main results of Osba et al. [7] on commutative VNL-rings are extended to right duo VNL-rings and even abelian GVNL-rings.

In this work we consider a complete spacelike submanifold $M^{n}$ immersed in the De Sitter space $S_{p}^{n+p}(1)$ with parallel mean curvature vector. We use a Simons type inequality to obtain some rigidity results characterizing umbilical submanifolds and hyperbolic cylinders in $S_p^{n+p}(1)$.

A method of choice for realizing finite groups as regular Galois groups over $\mathbb{Q}(T)$ is to find $\mathbb{Q}$-rational points on Hurwitz moduli spaces of covers. In another direction, the use of the so-called patching techniques has led to the realization of all finite groups over $\mathbb{Q}_p(T)$. Our main result shows that, under some conditions, these $p$-adic realizations lie on some special irreducible components of Hurwitz spaces (the so-called Harbater–Mumford components), thus connecting the two main branches of the area. As an application, we construct, for every projective system $(G_n)_{n\geq0}$ of finite groups, a tower of corresponding Hurwitz spaces $(\mathcal{H}_{G_n})_{n\geq0}$, geometrically irreducible and defined over some cyclotomic extension of $\mathbb{Q}$, which admits projective systems of $\mathbb{Q}_p^{\mathrm{ur}}$-rational points for all primes $p$ not dividing the orders $|G_n|$ ($n\geq0$).

Let $\Delta$ be one of the dual polar spaces $DW(5,q)$ or $DH(5,q^2)$. We consider a class of subspaces of $\Delta$, each member of which carries the structure of a near hexagon, and classify all these subspaces. Using this classification, we determine all hyperplanes of $DW(5,q)$ without ovoidal quads.

We show that the spherical subalgebra $U_{k,c}$ of the rational Cherednik algebra associated to $S_n C_{\ell}$, the wreath product of the symmetric group and the cyclic group of order $\ell$, is isomorphic to a quotient of the ring of invariant differential operators on a space of representations of the cyclic quiver of size $\ell$. This confirms a version of [5Conjecture 11.22] in the case of cyclic groups. The proof is a straightforward application of work of Oblomkov [12] on the deformed Harish–Chandra homomorphism, and of Crawley–Boevey, [3] and [4], and Gan and Ginzburg [7] on preprojective algebras.

We consider the standard action of the dihedral group $\bf{D}_n$ of order $2n$ on $\bf{C}$. This representation is absolutely irreducible and so the corresponding Hopf bifurcation occurs on $\bf{C} \oplus \bf{C}$. Golubitsky and Stewart (Hopf bifurcation with dihedral group symmetry: Coupled nonlinear oscillators. In: Multiparameter Bifurcation Series, M. Golubitsky and J. Guckenheimer, eds., Contemporary Mathematics 46, Am. Math. Soc., Providence, R.I. 1986, 131–173) and van Gils and Valkering (Hopf bifurcation and symmetry: standing and travelling waves in a circular chain. Japan J. Appl. Math.3, 207–222, 1986) prove the generic existence of three branches of periodic solutions, up to conjugacy, in systems of ordinary differential equations with $\bf{D}_n$-symmetry, depending on one real parameter, that present Hopf bifurcation. These solutions are found by using the Equivariant Hopf Theorem. We prove that generically, when $n\neq 4$ and assuming Birkhoff normal form, these are the only branches of periodic solutions that bifurcate from the trivial solution.

We provide a complete local classification of pseudo-parallel sub-manifolds with flat normal bundle of space forms, extending the classification by Dillen-Nölker for the semi-parallel case.

We combine the theory of sectorial sesquilinear forms with the theory of unbounded subnormal operators in Hilbert spaces to characterize the Friedrichs extensions of multiplication operators (with analytic symbols) in certain functional Hilbert spaces. Such characterizations lead to abstract Galerkin approximations and generalized wave equations.

In this paper, we classify 3-dimensional Lagrangian Willmore submanifolds of the nearly kaehler 6-sphere $S^6(1)$ with constant scalar curvature.

We determine for all $d$ and $p$ the maximal derived length of a soluble subgroup of the multiplicative group of a division ring of finite degree $d$ and characteristic $p\,\ge\,0$ to within one.

Par une méthode entièrement nouvelle utilisant les déformations $p$-adiques de pentes positives de représentations automorphes pour $\mathrm{GSp}_{4/\mathbb{Q}}$, nous prouvons que le $p$-groupe de Selmer $H^1_f(\mathbb{Q},V_f(k))$ associé à une forme modulaire $f$ de poids $2k$ et ordinaire en $p$ est infini si l’ordre d’annulation à l’entier $k$ de la fonction $L$ de $f$ est impair.

By an entirely new method that makes use of $p$-adic deformations of automorphic representations of $\mathrm{GSp}_{4/\mathbb{Q}}$, we prove that the $p$-adic Selmer group $H^1_f(\mathbb{Q},V_f(k))$ associated to a modular form $f$ of weight $2k$ that is ordinary at $p$ is infinite if the order of vanishing at $k$ of the $L$-function of $f$ is odd.

We present an elementary proof that if $A$ is a finite set of numbers, and the sumset $A+_GA$ is small, $|A+_GA|\leq c|A|$, along a dense graph $G$, then $A$ contains $k$-term arithmetic progressions.

For each group $G$ having an infinite normal subgroup with the relative property (T) (e.g. $G=H\times K$, with $H$ infinite with property (T) and $K$ arbitrary) and each countable abelian group $\varLambda$ we construct free ergodic measure-preserving actions $\sigma_\varLambda$ of $G$ on the probability space such that the first cohomology group of $\sigma_\varLambda$, $\ssm{H}^1(\sigma_\varLambda,G)$, is equal to $\text{Char}(G)\times\varLambda$. We deduce that $G$ has uncountably many non-stably orbit-equivalent actions. We also calculate 1-cohomology groups and show existence of ‘many’ non-stably orbit-equivalent actions for free products of groups as above.

Une conjecture de Grothendieck prédit que le transport parallèle de toute classe de cycle algébrique invariante par monodromie est encore une classe de cycle algébrique. Nous prouvons qu'il s'agit d'une conséquence des conjectures standard.

Dans un travail antérieur, nous avions démontré, en caractéristique nulle, une variante de cette conjecture de déformation, en remplaçant la notion de cycle algébrique par celle de cycle motivé (adjonction formelle des inverses des isomorphismes de Lefschetz attachés à des polarisations). Nous étendons ici ce résultat en caractéristique arbitraire, sous diverses hypothèses (par exemple si la base est ‘presque complète’).

Nous définissons inconditionnellement des groupes de Galois motiviques dans ce contexte, et étudions leur variation en famille.

A conjecture due to Grothendieck predicts that the parallel transport of any monodromy-invariant algebraic cycle class remains an algebraic cycle class. We prove that this follows from the standard conjectures.

We have shown in a previous work a variant of this deformation conjecture in characteristic zero, in which algebraic cycles are replaced by motivated cycles (formal adjunction of inverses of Lefschetz isomorphisms attached to polarizations). We extend this result in any characteristic under various assumptions, for instance if the base is ‘almost complete’.

We give an unconditional construction of motivic Galois groups in this context, and study their variation in a family of projective smooth varieties.

La conjecture de Tate pour les variétés abéliennes sur les corps finis a été prouvée par Tate lui-même dans le cas d'un $H^2$, mais reste ouverte en degré supérieur. Nous démontrons ici une variante affaiblie de cette conjecture (en tout degré), qui décrit néanmoins tout cycle de Tate ‘en termes de’ cycles algébriques. Cette variante s'applique aussi aux variétés abéliennes $A$ sur un corps de type fini sur un corps fini, au moins dans le cas ‘de bonne réduction’, i.e. dans le cas où $A$ est fibre générique d'un schéma abélien sur une base projective normale sur un corps fini.

Tate's conjecture for abelian varieties over finite fields has been proven by Tate himself for $H^2$ but remains open in higher degree. We prove a weaker version of the conjecture in any degree, which describes every Tate cycle `in terms of' algebraic cycles. This variant also applies to abelian varieties $A$ over finitely generated fields of characteristic $p$, at least in the `good reduction' case, i.e. when $A$ is the generic fibre of an abelian scheme on a normal projective variety defined over a finite field.