Narrow Results

We study the behavior of conductors of $L$-functions associated to certain Weil–Deligne representations under twisting. For each global field $K$ we prove a sharp upper bound for the conductor of the Rankin–Selberg $L$-function $L(A⊠B,s)$ where $A,B/K$ are abelian varieties.

Let C_i, i=1,2, be two smooth non-hyperelliptic curves over the complex numbers of genus g≥ 3, and connected étale double covers, such that the theta divisors Ξ_i of the associated Prym varieties (p_i, Ξ_i) are non singular in codimension ≤ 3. If are the norm maps, then Ξ_i is isomorphic to { and h⁰ (L) is even and positive}. Then the Abel maps define generic ℙ¹ bundles X_i→Ξ_i, where X_i is the special divisor variety and even}. We prove, under the hypotheses above, that biregular isomorphism of the special divisor varieties X₁≅ X₂ implies isomorphism of the double covers .

Let M be a complex projective manifold with the property that for any compact Riemann surface C and holomorphic map f : C → M the pullback of the tangent bundle of M is semistable. We prove that in this case M is a curve or a finite étale quotient of an abelian variety answering a conjecture of Biswas.

We study questions surrounding cup-product maps which arise from pairs of non-degenerate line bundles on an abelian variety. Important to our work is Mumford's index theorem which we use to prove that non-degenerate line bundles exhibit positivity analogous to that of ample line bundles. As an application we determine the asymptotic behavior of families of cup-product maps and prove that vector bundles associated to these families are asymptotically globally generated. To illustrate our results we provide several examples. For instance, we construct families of cup-product problems which result in a zero map on a one-dimensional locus. We also prove that the hypothesis of our results can be satisfied, in all possible instances, by a particular class of simple abelian varieties. Finally, we discuss the extent to which Mumford's theta groups are applicable in our more general setting.

In this paper, we give a detailed proof of a result due to Torsten Ekedahl, describing complex tori admitting a rigid group action and showing explicitly their projectivity and their structure in terms of CM-fields. In the appendix, joint with Claudon, we show, using a method of Green-Voisin, that all group actions on complex tori deform to projective ones.

In this paper, we discuss an interesting interaction between complex algebraic geometry and dynamics: the integrability of the Yang–Mills system for a field with gauge group SU(2) and the intersection of quartics in projective 4-space ℂℙ⁴. Using Enriques classification of algebraic surfaces and dynamics, we show that these two quartics intesect in the affine part of an abelian surface and it follows that the system of differential equations is algebraically completely integrable.

In this paper, we consider a dynamical system related to the Yang–Mills system for a field with gauge group SU(2). We solve this system in terms of genus two hyperelliptic functions. The corresponding invariant surface defined by the two constants of motion can be completed as a cyclic double cover of an abelian surface (the jacobian of a genus 2 curve) and we show that this system is algebraic completely integrable in the generalized sense. Also we show that this system is part of an algebraic completely integrable system in five unknowns having three constants of motion.

This work is the third part of a series of papers. In the first two, we considered curves and varieties in a power of an elliptic curve. Here, we deal with subvarieties of an abelian variety in general.

Let V be a proper irreducible subvariety of dimension d in an abelian variety A, both defined over the algebraic numbers. We say that V is weak-transverse if V is not contained in any proper algebraic subgroup of A, and transverse if it is not contained in any translate of such a subgroup.

Assume a conjectural lower bound for the normalized height of V. Then, for V transverse, we prove that the algebraic points of bounded height of V which lie in the union of all algebraic subgroups of A of codimension at least d + 1 translated by the points close to a subgroup Γ of finite rank, are non-Zariski-dense in V. If Γ has rank zero, it is sufficient to assume that V is weak-transverse. The notion of closeness is defined using a height function.

We show the existence of abelian surfaces over ℚ_p having good reduction with supersingular special fiber whose associated p-adic Galois module is not semisimple.

We generalize the existence of maximal orders in a semi-simple algebra for general ground rings. We also improve several statements in Chaps. 5 and 6 of Reiner's book [Maximal Orders, London Mathematical Society Monographs, Vol. 5 (Academic Press, London, 1975), 395 pp.] concerning separable algebras by removing the separability condition, provided the ground ring is only assumed to be Japanese, a very mild condition. Finally, we show the existence of maximal orders as endomorphism rings of abelian varieties in each isogeny class.

We formulate a geometric analog of the Titchmarsh divisor problem in the context of abelian varieties. For any abelian variety A defined over ℚ, we study the asymptotic distribution of the primes of ℤ which split completely in the division fields of A. For all abelian varieties which contain an elliptic curve we establish an asymptotic formula for such primes under the assumption of Generalized Riemann Hypothesis. We explain how to derive an unconditional asymptotic formula in the case that the abelian variety is a complex multiplication elliptic curve.

Let G be the product of an abelian variety and a torus defined over a number field K. The aim of this paper is detecting the dependence among some given rational points of G by studying their reductions modulo all primes of K. We show that if some simple conditions on the order of the reductions of the points are satisfied then there must be a dependency relation over the ring of K-endomorphisms of G. We generalize Larsen's result on the support problem to several points on products of abelian varieties and tori.

This paper proves a control theorem for the p-primary Selmer group of an abelian variety with respect to extensions of the form: Maximal pro-p extension of a number field unramified outside a finite set of primes R which does not include any primes dividing p in which another finite set of primes S splits completely. When the Galois group of the extension is not p-adic analytic, the control theorem gives information about p-ranks of Selmer and Tate–Shafarevich groups of the abelian variety. The paper also discusses what can be said in regards to a control theorem when the set R contains all the primes of the number field dividing p.

We construct p-adic L-functions associated to cuspidal Hilbert modular eigenforms of parallel weight two in certain dihedral or anticyclotomic extensions via the Jacquet–Langlands correspondence, generalizing works of Bertolini–Darmon, Vatsal and others. The construction given here is adelic, which allows us to deduce a precise interpolation formula from a Waldspurger-type theorem, as well as a formula for the dihedral μ-invariant. We also make a note of Howard's non-vanishing criterion for these p-adic L-functions, which can be used to reduce the associated Iwasawa main conjecture to a certain non-triviality criterion for families of p-adic L-functions.

In this paper, we will study the dynamical Manin–Mumford problem, focusing on the question of polarizability for endomorphisms of an abelian variety A and on the action of a Frobenius and its Verschiebung on the diagonal subvariety of A × A. We complete the study with different polarizability criteria.

We discuss the notion of polarized isogenies of abelian varieties, that is, isogenies which are compatible with given principal polarizations. This is motivated by problems of unlikely intersections in Shimura varieties. Our aim is to show that certain questions about polarized isogenies can be reduced to questions about unpolarized isogenies or vice versa. Our main theorem concerns abelian varieties $B$ which are isogenous to a fixed abelian variety $A$. It establishes the existence of a polarized isogeny $A\to B$ whose degree is polynomially bounded in $n$, if there exist both an unpolarized isogeny $A\to B$ of degree $n$ and a polarized isogeny $A\to B$ of unknown degree. As a further result, we prove that given any two principally polarized abelian varieties related by an unpolarized isogeny, there exists a polarized isogeny between their fourth powers. The proofs of both theorems involve calculations in the endomorphism algebras of the abelian varieties, using the Albert classification of these endomorphism algebras and the classification of Hermitian forms over division algebras.

In 1983, Silverman and Tate showed that the set of points in a 1-dimensional family of abelian varieties where a section of infinite order has “small height” is finite. We conjecture a generalization to higher-dimensional families, where we replace “finite” by “not Zariski dense.” We show that this conjecture would imply the uniform boundedness conjecture for torsion points on abelian varieties. We then prove a few special cases of this new conjecture.

We study the behavior under twisting of the Selmer rank parities of a self-dual prime-degree isogeny on a principally polarized abelian variety defined over a number field, subject to compatibility relations between the twists and the isogeny. In particular, we study isogenies on abelian varieties whose Selmer rank parities are related to the rank parities of elliptic curves with $j$-invariant 0 or 1728, assuming the Shafarevich–Tate conjecture. Using these results, we show how to classify the conjectural rank parities of all quartic or sextic twists of an elliptic curve defined over a number field, after a finite calculation. This generalizes the previous results of Hadian and Weidner on the behavior of $p$-Selmer ranks under $p$-twists.

We consider the identity component of the Sato–Tate group of the Jacobian of curves of the form

We approach this problem in three ways. First we use a theorem of Kani-Rosen to determine the splitting of Jacobians for $C_1$ curves of genus 4 and 5 and prove what the identity component of the Sato–Tate group is in each case. We then determine the splitting of Jacobians of higher genus $C_1$ curves by finding maps to lower genus curves and then computing pullbacks of differential 1-forms. In using this method, we are able to relate the Jacobians of curves of the form $C_1$, $C_2$ and $C_3$. Finally, we develop a new method for computing the identity component of the Sato–Tate groups of the Jacobians of the three families of curves. We use this method to compute many explicit examples, and find surprising patterns in the shapes of the identity components $S{T}^0(C)$ for these families of curves.

We study base field extensions of ordinary abelian varieties defined over finite fields using the module theoretic description introduced by Deligne. As applications we give algorithms to determine the minimal field of definition of such a variety and to determine whether two such varieties are twists.