Poitou–Tate duality over extensions of global fields

In this paper, we are interested in the Poitou–Tate duality in Galois cohomology. We will formulate and prove a theorem for a nice class of modules (with a continuous Galois action) over a pro-p ring. The theorem will comprise of the Tate local duality, Poitou–Tate duality and the Poitou–Tate?s exact sequence.     

On the Tate–Shafarevich group of Abelian schemes over higher dimensional bases over finite fields

We study analogues for the Tate–Shafarevich group for Abelian schemes with everywhere good reduction over higher dimensional bases over finite fields.     

Hilbert’s Tenth Problem for function fields of varieties over algebraically closed fields of positive characteristic

Let K be the function field of a variety of dimension ?? 2 over an algebraically closed field of odd characteristic. Then Hilbert??s Tenth Problem for K is undecidable. This generalizes the result by Kim and Roush from 1992 that Hilbert??s Tenth Problem for the purely transcendental function field ${{{\overline{\mathbb{F}}_p}}(t_1,t_2)}$ is undecidable when p?>?2.     

Schur–Weyl duality over finite fields

We prove a version of the Schur–Weyl duality over finite fields. We prove that for any field k, if k has at least r + 1 elements, the Schur–Weyl duality holds for the rth tensor power of a finite dimensional vector space V. Moreover, if the dimension of V is at least r + 1, the natural map ${{k\mathfrak{S}_r \to \mathsf{End}_{{\rm GL}(V)}(V^{\otimes r})}}We prove a version of the Schur–Weyl duality over finite fields. We prove that for any field k, if k has at least r + 1 elements, the Schur–Weyl duality holds for the rth tensor power of a finite dimensional vector space V. Moreover, if the dimension of V is at least r + 1, the natural map k\mathfrakS_r ? End_GL(V)(V^?r){{k\mathfrak{S}_r \to \mathsf{End}_{{\rm GL}(V)}(V^{\otimes r})}} is an isomorphism. This isomorphism may fail if dim _k V is not strictly larger than r.     

Equivariant Riemann–Roch theorems for curves over perfect fields

We prove an equivariant Riemann–Roch formula for divisors on algebraic curves over perfect fields. By reduction to the known case of curves over algebraically closed fields, we first show a preliminary formula with coefficients in . We then prove and shed some further light on a divisibility result that yields a formula with integral coefficients. Moreover, we give variants of the main theorem for equivariant locally free sheaves of higher rank.     

Isomorphism classes of Doche–Icart–Kohel curves over finite fields

We give explicit formulas for the number of distinct elliptic curves over a finite field, up to isomorphism, in two families of curves introduced by C. Doche, T. Icart and D.R. Kohel.     

A Rudin–Carleson theorem for planar vector fields

This paper generalizes the Rudin–Carleson theorem for homogeneous solutions of locally solvable real analytic vector fields.     

An improvement of the Hasse–Weil–Serre bound for curves over some finite fields

The Hasse–Weil–Serre bound is improved for low genus curves over finite fields with discriminant from $\{-3,-4,-7,-8\}$ by studying maximal and minimal curves.     

A Grothendieck–Lefschetz theorem for equivariant Picard groups

We prove a Grothendieck–Lefschetz theorem for equivariant Picard groups of non-singular varieties with finite group actions.     

The critical groups of a family of graphs and elliptic curves over finite fields

Let q be a power of a prime, and E be an elliptic curve defined over  . Such curves have a classical group structure, and one can form an infinite tower of groups by considering E over field extensions for all k≥1. The critical group of a graph may be defined as the cokernel of L(G), the Laplacian matrix of G. In this paper, we compare elliptic curve groups with the critical groups of a certain family of graphs. This collection of critical groups also decomposes into towers of subgroups, and we highlight additional comparisons by using the Frobenius map of E over  . This work was partially supported by the NSF, grant DMS-0500557 during the author’s graduate school at the University of California, San Diego, and partially supported by an NSF Postdoctoral Fellowship.     

On Mordell–Weil groups of isotrivial abelian varieties over function fields

We show that the Mordell–Weil rank of an isotrivial abelian variety with cyclic holonomy depends only on the fundamental group of the complement to the discriminant, provided the discriminant has singularities in CM class introduced here. This class of singularities includes all unibranched plane curves singularities. As a corollary, we describe a family of simple Jacobians over the field of rational functions in two variables for which the Mordell–Weil rank is arbitrarily large.     

The Nevo–Zimmer intermediate factor theorem over local fields

The Nevo–Zimmer theorem classifies the possible intermediate G-factors Y in Open image in new window , where G is a higher rank semisimple Lie group, P a minimal parabolic and X an irreducible G-space with an invariant probability measure. An important corollary is the Stuck–Zimmer theorem, which states that a faithful irreducible action of a higher rank Kazhdan semisimple Lie group with an invariant probability measure is either transitive or free, up to a null set. We present a different proof of the first theorem, that allows us to extend these two well-known theorems to linear groups over arbitrary local fields.     

The Eisenstein reciprocity law for formal Lubin–Tate groups

A generalized norm residue symbol on Lubin–Tate formal groups is studied. The triviality of this symbol in the case where the first argument belongs to the definition field of the formal group is investigated. Explicit formulas for the generalized norm residue symbol ( , ) _F,n are used. To this end, a restriction on the expansion of the first argument in powers of a uniformizer is removed. Bibliography: 6 titles.     

Springer��s theorem for tame quadratic forms over Henselian fields

A quadratic form over a Henselian-valued field of arbitrary residue characteristic is tame if it becomes hyperbolic over a tame extension. The Witt group of tame quadratic forms is shown to be canonically isomorphic to the Witt group of graded quadratic forms over the graded ring associated to the filtration defined by the valuation, hence also isomorphic to a direct sum of copies of the Witt group of the residue field indexed by the value group modulo 2.     

A topological characterization for closed sets under polar duality in ℚ n

A topological characterization is given for closed sets in ⁿ under the restriction of (cone) polar duality to ⁿ .     

Gallot–Tanno theorem for closed incomplete pseudo-Riemannian manifolds and applications

We extend the Gallot–Tanno theorem to closed pseudo-Riemannian manifolds. It is done by showing that if the cone over a manifold admits a parallel symmetric (0, 2)-tensor then it is Riemannian. Applications of this result to the existence of metrics with distinct Levi-Civita connections but having the same unparametrized geodesics and to the projective Obata conjecture are given. We also apply our result to show that the holonomy group of a closed (O(p + 1, q), S ^p,q )-manifold does not preserve any nondegenerate splitting of \mathbb R^p+1,q{\mathbb {R}^{p+1,q}}.