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Yuri G. Zarhin

Publications and source records attributed to Yuri G. Zarhin.

At least 91 records · Page 5Linked to original sources
arXiv2007

Cubic surfaces and cubic threefolds, jacobians and intermediate jacobians

In this paper we study principally polarized complex abelian varieties that admit an automorphism of order 3. It turns out that certain natural conditions on the multiplicities of its action on the differentials of the first kind do guarantee that those polarized varieties are not jacobians of curves. As an application, we get another proof of the already known (thanks to Clemens and Griffiths) fact that intermediate jacobians of certain cubic threefolds are not jacobians of curves.

math.AG↗
arXiv2006

Abelian varieties without homotheties

A celebrated theorem of Bogomolov asserts that the $\ell$-adic Lie algebra attached to the Galois action on the Tate module of an abelian variety over a number field contains all homotheties. This is not the case in characteristic $p$: a "counterexample" is provided by an ordinary elliptic curve defined over a finite field. In this note we discuss (and explicitly construct) more interesting examples of "non-constant" absolutely simple abelian varieties (without homotheties) over global fields in characteristic $p$.

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arXiv2006

Superelliptic jacobians

We discuss the structure of the endomorphism algebras of the jacobians of superelliptic curves y^q=f(x) where q is a prime power and f(x) is an irreducible cubic or quartic polynomial over the field of rational functions k(t) in characteristic zero, whose Galois group is the full symmetric group.

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arXiv2005

Non-isogenous superelliptic jacobians

In his previous papers (J. reine angew. Math. 544 (2002), 91--110; math.AG/0103203) the author introduced a certain explicit construction of superelliptic jacobians, whose endomorphism ring is the ring of integers in the $p$th cyclotomic field. (Here $p$ is an odd prime.) In the present paper we discuss when these jacobians are mutually non-isogenous. (The case of hyperelliptic jacobians was treated in author's e-print math.NT/0301173 .)

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arXiv2005

Finite linear groups, lattices, and products of elliptic curves

Let $V$ be a finite dimensional complex linear space and let $G$ be an irreducible finite subgroup of $\GL(V)$. For a $G$-invariant lattice $Λ$ in $V$ of maximal rank, we give a description of structure of the complex torus $V/Λ$. In particular, we prove that for a wide class of groups, $V/Λ$ is isogenous to a self-product of an elliptic curve, and that in many cases $V/Λ$ is isomorphic to a product of mutually isogenous elliptic curves with complex multiplication. We show that there are $G$ and $Λ$ such that the complex torus $V/Λ$ is not an abelian variety but one can always replace $Λ$ by another $G$-invariant lattice $Δ$ such that $V/Δ$ is a product if elliptic curves with complex multiplication. We amplify these results with a criterion, in terms of the character and the Schur $\mathbf Q$-index of $G$-module $V$, of the existence of a nonzero $G$-invariant lattice in $V$.

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arXiv2004

Homomorphisms of abelian varieties

We discuss Galois properties of points of prime order on an abelian variety that imply the simplicity of its endomorphism algebra. Applications to hyperelliptic jacobians are given. In particular, we improve some of our earlier results.

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arXiv2004

Non-supersingular Hyperelliptic jacobians

In his previous papers the author proved that in characteristic different from 2 the jacobian J(C) of a hyperelliptic curve C: y^2=f(x) has only trivial endomorphisms over an algebraic closure K_a of the ground field K if the Galois group of the irreducible polynomial f(x) in K[x] is either the full symmetric group S_n or the alternating group A_n. Here n > 8 is the degree of f. The goal of this paper is to extend this result to the case when either n=7,8 or n=5,6 and char(K)>3.

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arXiv2003

Cyclic covers of prime power degree, jacobians and endomorphisms

Suppose that $K$ is a field of characteristic 0, $K_a$ is its algebraic closure, $p$ is a prime, $q=p^r$ is a power prime. Suppose that $f(x) \in K[x]$ is a polynomial of degree $n > 4$ without multiple roots. Let us consider the superelliptic curve $C: y^q=f(x)$ and its jacobian $J(C)$. We study the endomorphism algebra $End^0(J(C))$ of all $K_a$-endomorphisms of $J(C)$. We prove that $End^0(J(C))$ is "as small as possible" if the Galois group of $f$ over $K$ is either the full symmetric group $S_n$ or the alternating group $A_n$.

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arXiv2003

Hyperelliptic jacobians without complex multiplication and Steinberg representations in positive characteristic

In his previous papers (Math. Res. Letters 7 (2000), 123--13; Math. Res. Letters 8 (2001), 429--435; Moscow Math. J. 2 (2002), issue 2, 403-431) the author proved that in characteristic $\ne 2$ the jacobian $J(C)$ of a hyperelliptic curve $C: y^2=f(x)$ has only trivial endomorphisms over an algebraic closure $K_a$ of the ground field $K$ if the Galois group $\Gal(f)$ of the irreducible polynomial $f(x) \in K[x]$ is either the symmetric group $\Sn$ or the alternating group $\A_n$. Here $n\ge 9$ is the degree of $f$. The goal of this paper is to extend this result to the case of certain ``smaller'' doubly transitive simple Galois groups. Namely, we treat the infinite series $n=2^m+1, \Gal(f)=Ł_2(2^m):=\PSL_2(\F_{2^m})$, $n=2^{4m+2}+1, \Gal(f)=\Sz(2^{2m+1})= {^2\B_2}(2^{2m+1})$ and $n=2^{3m}+1, \Gal(f)=\U_3(2^m):=\PSU_3(\F_{2^m})$.

math.NT↗
arXiv2003

The Tate Conjecture for Powers of Ordinary Cubic Fourfolds Over Finite Fields

Recently N. Levin (Comp. Math. 127 (2001), 1--21) proved the Tate conjecture for ordinary cubic fourfolds over finite fields. In this paper we prove the Tate conjecture for self-products of ordinary cubic fourfolds. Our proof is based on properties of so called polynomials of K3 type introduced by the author (Duke Math. J. 72 (1993), 65--83).

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arXiv2003

Very simple representations: variations on a theme of Clifford

We discuss a certain class of absolutely irreducible group representations that behave nicely under the restriction to normal subgroups and subalgebras. These representations proved to be useful for the construction of abelian varieties with small endomorphism rings.

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arXiv2002

The endomorphism rings of jacobians of cyclic covers of the projective line

Suppose K is a field of characteristic 0, $K_a$ is its algebraic closure, p is an odd prime. Suppose, $f(x) \in K[x]$ is a polynomial of degree $n \ge 5$ without multiple roots. Let us consider a curve $C: y^p=f(x)$ and its jacobian J(C). It is known that the ring End(J(C)) of all $K_a$-endomorphisms of J(C) contains the ring $Z[ζ_p]$ of integers in the pth cyclotomic field (generated by obvious automorphisms of C). We prove that $End(J(C))=Z[ζ_p]$ if the Galois group of f over K is either the symmetric group $S_n$ or the alternating group $A_n$.

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arXiv2002

Hyperelliptic jacobians without complex multiplication, doubly transitive permutation groups and projective representations

In his previous paper (Math. Res. Letters 7(2000), 123--132) the author proved that in characteristic zero the jacobian $J(C)$ of a hyperelliptic curve $C: y^2=f(x)$ has only trivial endomorphisms over an algebraic closure $K_a$ of the ground field $K$ if the Galois group $Gal(f)$ of the irreducible polynomial $f(x) \in K[x]$ is either the symmetric group $S_n$ or the alternating group $A_n$. Here $n>4$ is the degree of $f$. In the next paper (Progress in Math. 195(2001), 473--490) we extended this result to the case of certain``smaller'' Galois groups. In particular, we treated the infinite series $n=2^r+1, Gal(f)=L_2(2^r)$. The case of small Mathieu groups $M_n$ (with $n=11,12)$ was also treated. In this paper we do the case of large Mathieu groups $M_n$ (with $n=22,23,24$). We also treat the infinite series $Gal(f)=L_m(2^r)$ (with $m>2$ except the cases $(m,r)=(3,2)$ or $(4,1)$), assuming that the set $R$ of roots of $f$ can be identified with the corresponding projective space $P^{m-1)(F_{2^r})$ over the finite field $F_{2^r}$ of characteristic 2 in such a way that the Galois action on $R$ becomes the natural action of $L_m(2^r)$ on the projective space.

math.AG↗
arXiv2001

Very simple 2-adic representations and hyperelliptic jacobians

Let $K$ be a number field, $n>4$ an integer, $f(x)$ an irreducible polynomial over $K$ of degree $n$, whose Galois group is either the full symmetric group $S_n$ or the alternating group $A_n$. Suppose $C:y^2=f(x)$ is the corresponding hyperelliptic curve and $J$ its jacobian defined over $K$. For each prime $\ell$ we write $V_{\ell}(J)$ for the $Q_{\ell}$-Tate module of $J$ and $e_{\ell}$ for the Riemann form on $V_{\ell}(J)$ attached to the theta divisor. (Here $Q_{\ell}$ is the field of $\ell$-adic numbers.) We write $sp(V_{\ell}(J))$ for the $Q_{\ell}$-Lie algebra of the symplectic group of $e_{\ell}$. We write $g_{\ell}$ for the Lie algebra of the image of the Galois group $Gal(K)$ of $K$ in $Aut(V_{\ell}(J))$. We prove that $g_{\ell}$ coincides with the direct sum $Q_{\ell}I \oplus sp(V_{\ell}(J))$ where $I$ is the identity operator.

math.AG↗
arXiv2001

Hyperelliptic jacobians and $\U_3(2^m)$

In his previous paper (Math. Res. Letters 7(2000), 123--132) the author proved that in characteristic zero the jacobian $J(C)$ of a hyperelliptic curve $C: y^2=f(x)$ has only trivial endomorphisms over an algebraic closure $K_a$ of the ground field $K$ if the Galois group $Gal(f)$ of the irreducible polynomial $f(x) \in K[x]$ is either the symmetric group $S_n$ or the alternating group $A_n$. Here $n>4$ is the degree of $f$. In math.AG/0003002 we extended this result to the case of certain ``smaller'' Galois groups. In particular, we treated the infinite series $n=2^r+1, Gal(f)=L_2(2^r)$ and $n=2^{4r+2}+1, Gal(f)=Sz(2^{2r+1})$. In this paper we do the case of $Gal(f)=\U_3(2^m)$ and $n=2^{3m}+1$.

math.AG↗
arXiv2001

Cyclic covers of the projective line, their jacobians and endomorphisms

We study the endomorphism ring $End(J(C))$ of the complex jacobian $J(C)$ of a curve $y^p=f(x)$ where $p$ is an odd prime and $f(x)$ is a polynomial with complex coefficiens of degree $n>4$ and without multiple roots. Assume that all the coefficients of $f$ lie in a (sub)field $K$ and the Galois group of $f$ over $K$ is either the full symmetric group $S_n$ or the alternating group $A_n$. Then we prove that $End(J(C))$ is the ring of integers in the in the $p$th cyclotomic field, if $p$ is a Fermat prime (e.g., $p=3,5,17,257$). Similar results for $p=2$ (the case of hyperelliptic curves) were obtained by the author in Math. Res. Lett. 7(2000), 123--132.

math.AG↗
arXiv2001

Hyperelliptic jacobians and projective linear Galois groups

In his previous paper (Math. Res. Letters 7(2000), 123--132) the author proved that in characteristic zero the jacobian $J(C)$ of a hyperelliptic curve $C: y^2=f(x)$ has only trivial endomorphisms over an algebraic closure $K_a$ of the ground field $K$ if the Galois group $Gal(f)$ of the irreducible polynomial $f(x) \in K[x]$ is either the symmetric group $S_n$ or the alternating group $A_n$. Here $n>4$ is the degree of $f$. In math.AG/0003002 we extended this result to the case of certain ``smaller'' Galois groups. In particular, we treated the infinite series $n=2^r+1, Gal(f)=L_2(2^r)$ and $n=2^{4r+2}+1, Gal(f)=Sz(2^{2r+1})$. In the present paper we prove that $J(C)$ has only trivial endomorphisms over $K_a$ if the set of roots of $f$ could be identified with the $(m-1)$-dimensional projective space $P^{m-1}(F_q)$ over a finite field $F_q$ of odd characteristic in such a way that $Gal(f)$, viewed as its permutation group, becomes either the projective linear group $PGL(m,F_q)$ or the projective special linear group $L_m(q):=PSL(m,F_q)$. Here we assume that $m>2$.

math.AG↗
arXiv2001

Hyperelliptic jacobians without complex multiplication in positive characteristic

We prove that in odd characteristic the jacobian of a hyperelliptic curve $y^2=f(x)$ has no nontrivial endomorphisms over an algebraic closure of the ground field if the Galois group of the polynomial $f$ of even degree is ``very big". The case of characteristic zero was previously treated by the author (Math. Res. Letters 7(2000), 123--132).

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