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Yu. G. Zarhin

Publications and source records attributed to Yu. G. Zarhin.

15 recordsLinked to original sources
arXiv2021

Homomorphisms of hyperelliptic jacobians

In his previous papers (Math. Res. Letters 7 (2000), 123--13; Progress in Math. 195 (2001), 473--490; Math. Res. Letters 8 (2001), 429--435; Moscow Math. J. 2 (2002), issue 2, 403-431; Proc. Amer. Math. Soc. 131 (2003), no. 1, 95--102) the author introduced certain explicit constructions of hyperelliptic jacobians without nontrivial endomorphisms. In the present paper we discuss when these jacobians are mutually non-isogenous. In addition, a special case ($n=m=3$) of our Theorem 1.2 provides the following criterion for elliptic curves $C_f: y^2=f(x)$ and $C_h: y^2=h(x)$ to be non-isogenous. (Here $f(x)$ and $h(x)$ are cubic polynomials with coefficients in a field $K$ of characteristic zero.) Suppose that $f(x)$ and $h(x)$ are irreducible over $K$, their Galois groups over $K$ coincide with the full symmetric group $S_3$, and their splitting fields are linearly disjoint over $K$. Then the elliptic curves $C_f$ and $C_h$ are non-isogenous over an algebraic closure of $K$.

math.NT↗
arXiv2015

Isogenies of abelian varieties over finite fields

In this paper we give conditions under which two abelian varieties that are defined over a finite field $F$, and are isogenous over some larger field, are $F$-isogenous. Further, we give conditions under which a given isogeny is defined over $F$.

math.NT↗
arXiv2000

Symplectic representations of inertia groups

Suppose $\ell$ is a prime number, $\ell >3$, $K$ is a field that is an unramified finite extension of the field $\Q_\ell$ of $\ell$-adic numbers, and $G$ is a finite group that is a semi-direct product of a normal $\ell'$-subgroup $H$ and a cyclic $\ell$-group $L$. Suppose that the group algebra $K[H]$ is decomposable. If there exists an embedding of $G$ in the symplectic group $\Sp_{2d}(K)$ for some positive integer $d$, then there exists an embedding of $G$ in $\Sp_{2d}({\mathcal O}_K)$, where ${\mathcal O}_K$ is the ring of integers of $K$.

math.NT↗
arXiv2000

Polarizations on abelian varieties

The results in this paper imply that for every number field F and positive integer r, there exists an F-isogeny class of abelian varieties such that r divides the degree of every F-polarization on every abelian variety in the isogeny class.

math.AG↗
arXiv1999

Étale cohomology and reduction of abelian varieties

In this paper we study the étale cohomology groups associated to abelian varieties. We obtain necessary and sufficient conditions for an abelian variety to have semistable reduction (or purely additive reduction which becomes semistable over a quadratic extension) in terms of the action of the absolute inertia group on the étale cohomology groups with finite coefficients.

math.AG↗
arXiv1999

Hodge classes on abelian varieties of low dimension

In this paper we study Hodge classes on complex abelian varieties. We prove some general results that allow us, in certain cases, to compute the Hodge group of a product abelian variety $X = X_1 \times X_2$ once we know the Hodge groups of the two factors. Using these results we can compute the Hodge groups of all abelian varieties of dimension $\leq 5$. We prove that the Hodge ring of any such abelian variety $X$ is generated by divisor classes together with the so-called Weil classes on (quotients of) $X$.

math.AG↗
arXiv1998

Modular representations arising from self-dual $\ell$-adic representations of finite groups

Suppose $\ell$ is a prime number, ${\mathbf Q}_\ell$ is the field of $\ell$-adic numbers, ${\mathbf F}_\ell$ is the finite field of $\ell$ elements, and $d$ is a positive integer. Suppose $G$ is a finite subgroup of a symplectic group $Sp_{2d}({\mathbf Q}_\ell)$. We prove that $G$ can be embedded in $Sp_{2d}({\mathbf F}_\ell)$ in such a way that the characteristic polynomials are preserved (mod $\ell$), as long as $\ell>3$.

math.GR↗
arXiv1998

Reduction of abelian varieties

We study semistable reduction and torsion points of abelian varieties. In particular, we give necessary and sufficient conditions for an abelian variety to have semistable reduction. We also study Néron models of abelian varieties with potentially good reduction and torsion points of small order. We study some invariants that measure the extent to which an abelian variety with potentially good reduction fails to have good reduction.

alg-geom↗
arXiv1998

Subgroups of inertia groups arising from abelian varieties

Given an abelian variety over a field with a discrete valuation, Grothendieck defined a certain open normal subgroup of the absolute inertia group. This subgroup encodes information on the extensions over which the abelian variety acquires semistable reduction. We study this subgroup, and use it to obtain information on the extensions over which the abelian variety acquires semistable reduction.

alg-geom↗
arXiv1996

Weil classes on abelian varieties

Consider a complex abelian variety X on which a field F acts. Generalizing a construction of A. Weil, one associates to this a subspace W_F of the cohomology of X, which we call the space of Weil classes w.r.t. F. The purpose of this paper is to answer the following two questions: Q1: under what conditions on F does the space W_F contain, or even consist of, Hodge classes?, Q2: if W_F contains Hodge classes, under what conditions on F are these exceptional? In case X is defined over a number field, we also answer the analogous questions for Tate classes.

alg-geom↗
arXiv1996

p-adic abelian integrals and commutative Lie groups

The aim of this paper is to propose an ``elementary" approach to Coleman's theory of p-adic abelian integrals. Our main tool is a theory of commutative p-adic Lie groups (the logarithm map); we use neither dagger analysis nor Monsky-Washnitzer cohomology theory. Notice that we also treat the case of bad reduction. A preliminary version of this paper appeared as Exposé 9 dans ``Problemes Diophantiens 88-89" (D. Bertrand, M. Waldschmidt), Publ. Math. Univ. Paris VI 90(1990), 15 pp.

alg-geom↗
arXiv1996

Connectedness extensions for abelian varieties

Suppose $A$ is an abelian variety over a field $F$, and $\ell$ is a prime not equal to the characteristic of $F$. Let $F_{Φ,\ell}(A)$ denote the smallest extension of $F$ such that the Zariski closure of the image of the $\ell$-adic representation associated to $A$ is connected. Serre introduced this field, and proved that when $F$ is a finitely generated extension of ${\mathbf Q}$, $F_{Φ,\ell}(A)$ does not depend on the choice of $\ell$. In this paper we study extensions $F_{Φ,\ell}(B)/F$ for twists $B$ of a given abelian variety, especially when the abelian varieties are of Weil type.

alg-geom↗
arXiv1996

Images of $\ell$-adic representations and automorphisms of abelian varieties

Suppose $F$ is either a global field or a finitely generated extension of ${\mathbf Q}$, $A$ is an abelian variety over $F$, and $\ell$ is a prime not equal to the characteristic of $F$. Let $Z$ denote the center of the endomorphism algebra of $A$. Let $G$ denote the group of ${\mathbf Q}_\ell$-points of the identity connected component of the Zariski closure of the image of the $\ell$-adic representation associated to $A$. We prove the $\ell$-independence of the intersection of $G$ with the torsion subgroup of $Z$. Our results provide evidence in the direction of the Mumford-Tate Conjecture.

alg-geom↗
arXiv1995

Hodge groups of abelian varieties with purely multiplicative reduction

The main result of the paper is that if $A$ is an abelian variety over a subfield $F$ of ${\bold C}$, and $A$ has purely multiplicative reduction at a discrete valuation of $F$, then the Hodge group of $A$ is semisimple. Further, we give necessary and sufficient conditions for the Hodge group to be semisimple. We obtain bounds on certain torsion subgroups for abelian varieties which do not have purely multiplicative reduction at a given discrete valuation, and therefore obtain bounds on torsion for abelian varieties, defined over number fields, whose Hodge groups are not semisimple.

alg-geom↗