Permutation polynomials from trace functions over finite fields

In this paper, we propose several classes of permutation polynomials based on trace functions over finite fields of characteristic 2. The main result of this paper is obtained by determining the number of solutions of certain equations over finite fields.     

New classes of permutation binomials and permutation trinomials over finite fields

Permutation polynomials over finite fields play important roles in finite fields theory. They also have wide applications in many areas of science and engineering such as coding theory, cryptography, combinatorial design, communication theory and so on. Permutation binomials and permutation trinomials attract people's interest due to their simple algebraic forms and additional extraordinary properties. In this paper, we find a new result about permutation binomials and construct several new classes of permutation trinomials. Some of them are generalizations of known ones.     

The groups of points on abelian varieties over finite fields

Let A be an abelian variety with commutative endomorphism algebra over a finite field k. The k-isogeny class of A is uniquely determined by a Weil polynomial f _A without multiple roots. We give a classification of the groups of k-rational points on varieties from this class in terms of Newton polygons of f _A (1 − t).     

Normal sequences over finite abelian groups

In this note, we obtain the structure of short normal sequences over a finite abelian p-group or a finite abelian group of rank two, thus answering positively a conjecture of Gao and Zhuang for various groups. The results obtained here improve all known results on this conjecture.     

Vanishing theorems for constructible sheaves on abelian varieties over finite fields

Let \(\kappa \) be a field, finitely generated over its prime field, and let k denote an algebraically closed field containing \(\kappa \). For a perverse \(\overline{\mathbb {Q}}_\ell \)-adic sheaf \(K_0\) on an abelian variety \(X_0\) over \(\kappa \), let K and X denote the base field extensions of \(K_0\) and \(X_0\) to k. Then, the aim of this note is to show that the Euler–Poincare characteristic of the perverse sheaf K on X is a non-negative integer, i.e. \(\chi (X,K)=\sum _\nu (-1)^\nu \dim _{\overline{\mathbb {Q}}_\ell }(H^\nu (X,K))\ge 0\). This generalizes the result of Franecki and Kapranov [9] for fields of characteristic zero. Furthermore we show that \(\chi (X,K)=0\) implies K to be translation invariant. This result allows to considerably simplify the proof of the generic vanishing theorems for constructible sheaves on complex abelian varieties of [11]. Furthermore it extends these vanishing theorems to constructible sheaves on abelian varieties over finite fields.     

The characteristic polynomials of abelian varieties of dimensions 3 over finite fields

We describe the set of characteristic polynomials of abelian varieties of dimension 3 over finite fields.     

Sparse univariate polynomials with many roots over finite fields

Suppose q is a prime power and $f\in {\mathbb{F}}_q[x]$ is a univariate polynomial with exactly t monomial terms and degree $<q-1$. To establish a finite field analogue of Descartes' Rule, Bi, Cheng, and Rojas (2013) proved an upper bound of $2{(q-1)}^{\frac{t-2}{t-1}}$ on the number of cosets in ${\mathbb{F}}_q^{⁎}$ needed to cover the roots of f in ${\mathbb{F}}_q^{⁎}$. Here, we give explicit f with root structure approaching this bound: When q is a perfect $(t-1)$-st power we give an explicit t-nomial vanishing on $q^{\frac{t-2}{t-1}}$ distinct cosets of ${\mathbb{F}}_q^{⁎}$. Over prime fields ${\mathbb{F}}_p$, computational data we provide suggests that it is harder to construct explicit sparse polynomials with many roots. Nevertheless, assuming the Generalized Riemann Hypothesis, we find explicit trinomials having $\mathrm{\Omega }\left(\frac{\log p}{\log \log p}\right)$ distinct roots in ${\mathbb{F}}_p$.     

The loci of abelian varieties with points of high multiplicity on the theta divisor

We study the loci of principally polarized abelian varieties with points of high multiplicity on the theta divisor. Using the heat equation and degeneration techniques, we relate these loci and their closures to each other, as well as to the singular set of the universal theta divisor. We obtain bounds on the dimensions of these loci and relations among their dimensions, and make further conjectures about their structure. Research of the first author is supported in part by National Science Foundation under the grant DMS-05-55867.     

The number of irreducible polynomials over finite fields of characteristic 2 with given trace and subtrace

In this paper we obtained the formula for the number of irreducible polynomials with degree n over finite fields of characteristic two with given trace and subtrace. This formula is a generalization of the result of Cattell et al. (2003) [2].     

Modularity of abelian varieties over Q with bad reduction in one prime only

We show that certain abelian varieties over Q with bad reduction at one prime only are modular by using methods based on the tables of Odlyzko and class field theory.     

Linear recurring sequence subgroups in finite fields

Given a finite field and a linear recurrence relation over it is possible to find, in a fairly “obvious” way, a finite extension of and a subgroup M of the multiplicative group of such that the elements of M may be written, without repetition, so as to form a cyclically closed sequence which obeys the recurrence. Here we investigate this phenomenon for second-order recurrences; the situation in which has prime order and the characteristic polynomial of the relation is irreducible over is described.