On the Representation of Primes by Cubic Polynomials in Two Variables

In an earlier paper (see Proc. London Math. Soc. (3) 84 (2002)257–288) we showed that an irreducible integral binarycubic form f(x, y) attains infinitely many prime values, providingthat it has no fixed prime divisor. We now extend this resultby showing that f(m, n) still attains infinitely many primevalues if m and n are restricted by arbitrary congruence conditions,providing that there is still no fixed prime divisor. Two immediate consequences for the solvability of diagonal cubicDiophantine equations are given. 2000 Mathematics Subject Classification11N32 (primary), 11N36, 11R44 (secondary).     

Long Arithmetic Progressions in Sum-Sets and the Number x-Sum-Free Sets

In this paper we obtain optimal bounds for the length of thelongest arithmetic progression in various kinds of sum-sets.As an application, we derive a sharp estimate for the numberof sets A of residues modulo a prime n such that no subsum ofA equals x modulo n, where x is a fixed residue modulo n. 2000Mathematics Subject Classification 05A16, 11B25, 11P32.     

On Hill's Equation with a Singular Complex-Valued Potential

In this paper Hill's equation y' + qy = Ey, where q is a complex-valuedfunction with inverse square singularities, is studied. Resultson the dependence of solutions to initial value problems onthe parameter E and the initial point x₀, on the structure ofthe conditional stability set, and on the asymptotic distributionof (semi-)periodic and Sturm-Liouville eigenvalues are obtained.It is proved that a certain subset of the set of Floquet solutionsis a line bundle on a certain analytic curve in C². We establishnecessary and sufficient conditions for q to be algebro-geometric,that is, to be a stationary solution of some equation in theKorteweg-de Vries (KdV) hierarchy. To do this a distinctionbetween movable and immovable Dirichlet eigenvalues is employed.Finally, an example showing that the finite-band property doesnot imply that q is algebro-geometric is given. This is in contrastto the case where q is real and non-singular. 1991 MathematicsSubject Classification: 34L40, 14H60.     

Cm Elliptic Curves and Bicolorings of Steiner Triple Systems

It is shown that a necessary condition for the existence ofa bicolored Steiner triple system of order n is that n can bewritten in the form A²+3B² for integers A and B. In the casewhen n=q is either a prime congruent to 1 mod 3, or the squareof a prime congruent to 2 mod 3, it is shown that the numbersof colored vertices in the triple system would be unique, andare given by the number of points on specific twists of theCM elliptic curve y²=x³–1 over the finite field F_q. 2000Mathematics Subject Classification 05B07, 11G20, 14G15 (primary);11G15, 14K22 (secondary).     

Properties of large prime divisors of numbers of the form p − 1

The main result of this paper is the fact that the fraction of primes p ≤ x satisfying the condition that p ? 1 has a prime divisor q > exp(ln x/ln ln x) and the number of prime divisors of q ? 1 essentially differ from ln ln(x/n), where n = (p ? 1)/q, tends to zero as x increases.     

Embedded Thick Finite Generalized Hexagons in Projective Space

We show that every embedded finite thick generalized hexagon of order (s, t) in PG(n,q) which satisfies the conditions

1. s = q
2. the set of all points of generates PG(n, q)
3. for anypoint x of , the set of all points collinear in withx is containedin a plane of PG(n, q)
4. for any point x of , the set of allpoints of not oppositex in is contained in a hyperplane ofPG,(n, q)

is necessarily the standard representation of H(q) in PG(6,q) (on the quadric Q(6, q)), the standard representation ofH(q) for q even in PG(5, q) (inside a symplectic space), orthe standard representation of H(q, ) in PG(7, q) (where the lines of are the lines fixed by a trialityon the quadric Q⁺(7, q)). This generalizes a result by Cameronand Kantor [3], which is used in our proof.     

Lacunary Polynomials, Multiple Blocking Sets and Baer Subplanes

New lower bounds are given for the size of a point set in aDesarguesian projective plane over a finite field that containsat least a prescribed number s of points on every line. Thesebounds are best possible when q is square and s is small comparedwith q. In this case the smallest set is shown to be the unionof disjoint Baer subplanes. The results are based on new resultson the structure of certain lacunary polynomials, which canbe regarded as a generalization of Rédei's results inthe case when the derivative of the polynomial vanishes.     

Kazhdan-Lusztig Cells, q-Schur Algebras and James' Conjecture

We consider the Dipper–James q-Schur algebra S_q(n, r)_k,defined over a field k and with parameter q 0. An understandingof the representation theory of this algebra is of considerableinterest in the representation theory of finite groups of Lietype and quantum groups; see, for example, [6] and [11]. Itis known that S_q(n, r)_k is a semisimple algebra if q is nota root of unity. Much more interesting is the case when S_q(n,r)_k is not semisimple. Then we have a corresponding decompositionmatrix which records the multiplicities of the simple modulesin certain ‘standard modules’ (or ‘Weyl modules’).A major unsolved problem is the explicit determination of thesedecomposition matrices.     

A characterization of finite soluble groups

Let G be a finite soluble group of order m and let w(x₁, ...,x_n) be a group word. Then the probability that w(g₁, ..., g_n)= 1 (where (g₁, ..., g_n) is a random n-tuple in G) is at leastp^–(m–t), where p is the largest prime divisor ofm and t is the number of distinct primes dividing m. This contrastswith the case of a non-soluble group G, for which Abérthas shown that the corresponding probability can take arbitrarilysmall positive values as n .     

Flat Cyclotomic Polynomials of Order Three

A cyclotomic polynomial _n is said to be of order 3 if n = pqrfor three distinct odd primes p, q, and r. We establish theexistence of an infinite family of such polynomials whose coefficientsdo not exceed 1 in modulus. 2000 Mathematics Subject Classification11B83, 11C08.     

Hurwitz Groups with Given Centre

A Hurwitz group is any non-trivial finite group that can be(2,3,7)-generated; that is, generated by elements x and y satisfyingthe relations x² = y³ = (xy)⁷ = 1. In this short paper a completeanswer is given to a 1965 question by John Leech, showing thatthe centre of a Hurwitz group can be any given finite abeliangroup. The proof is based on a recent theorem of Lucchini, Tamburiniand Wilson, which states that the special linear group SL_n(q)is a Hurwitz group for every integer n 287 and every prime-powerq. 2000 Mathematics Subject Classification 20F05 (primary);57M05 (secondary).     

The Numerical Calculation of Odd-degree Polynomial Splines with Equi-spaced Knots

Constructive equations for polynomial splines of odd-degree2r+1 with knots x₁ = x₀+ih, i = 0(1)n are formulated in termsof even-order derivatives, odd-order derivatives being givenby explicit formulae which are shown to be identical with truncatedTaylor series expansions of the same form. The defining equationsare written in a manner which reveals a strong connection withthe well-known Numerov formula. Solution of the equations byblock iterative methods is considered for the case when evenderivatives are specified at x = x₀ and x_n. Block Jacobi andblock Gauss—Seidel iteration are shown to be convergentfor all positive r and optimum acceleration parameters for blockS.O.R. are given for r = 2(1)6. It is shown that distinct computationaladvantages result from relaxing the condition for a true splinefit and considering instead a truncated spline of higher order.     

SCALED ASYMPTOTICS FOR SOME q-SERIES

This work, investigates the asymptotics for Euler’s q-exponentialE_q(z), Ramanujan’s function A_q(z), Jackson’s q-Besselfunction J_v⁽²⁾ (z; q), the Stieltjes–Wigert orthogonalpolynomials S_n(x; q) and q-Laguerre polynomials L_n⁽⁾ (x; q)as q approaches 1.     

Global stability in difference equations satisfying the generalized Yorke condition

We present several conditions sufficient for global stability of the zero solution of nonautonomous difference equation xn+1=qxn+fn(xn,…,xn−k), n∈Z, when the nonlinearities fn satisfy a sort of negative feedback condition. Moreover, for every k∈N, we indicate qk such that one of our stability conditions is sharp if q∈(0,qk]. We apply our results to discrete versions of Nicholson's blowflies equation, the Mackey-Glass equations, and the Wazewska and Lasota equation.     

Bounds on the extensional strains in elastic homogeneous crystals under simple tension

Within the context of the linearized theory of elasticity, weconsider homogeneous crystals, which have orthorhombic, tetragonal,hexagonal symmetry or cubic symmetry (‘RTHC’ crystals).When such a crystal is subjected to a simple tension (or compression)of amount T in the direction n, there will be three, generallydifferent, extensional strains along the three mutually perpendiculardirections corresponding to the principal axes of strain. Thepurpose of this paper is to present a simple procedure to placebounds, upper and lower, on the possible extensional strainsin the crystal, both in the case when n is fixed in directionand in the case when n is arbitrary. The procedure allows usto determine whether the bounds are attained or not.     

Linear Forms in two m-adic Logarithms and Applications to Diophantine Problems

We give sharp, explicit estimates for linear forms in two logarithms, simultaneously for several non-Archimedean valuations. We present applications to explicit lower bounds for the fractional part of powers of rational numbers, and to the Diophantine equation (x ⁿ – 1)/(x – 1) = y ^q .     

On Waring's Problem for Cubes and Smooth Weyl Sums

Non-trivial estimates for fractional moments of smooth cubicWeyl sums are developed. Complemented by bounds for such sumsof use on both the major and minor arcs in a Hardy-Littlewooddissection, these estimates are applied to derive an upper boundfor the sth moment of the smooth cubic Weyl sum of the expectedorder of magnitude as soon as s> 7.691. Related argumentsdemonstrate that all large integers n are represented as thesum of eight cubes of natural numbers, all of whose prime divisorsare at most exp (c(log nlog log n)^1/2}, for a suitable positivenumber c. This conclusion improves a previous result of G. Harcosin which nine cubes are required. 1991 Mathematics Subject Classification:11P05, 11L15, 11P55.     

Low-Dimensional Representations of Special Linear Groups in Cross Characteristics

The low-dimensional projective irreducible representations incross characteristics of the projective special linear groupPSL_n(q) are investigated. If n 3 and (n, q) (3,2), (3,4), (4,2), (4,3), all such representationsof the first degree (which is (qⁿ – q)/(q – 1) – with = 0 or 1) and the second degree (which is (qⁿ –1)/(q – 1) come from Weil representations. We show thatthe gap between the second and the third degree is roughly q^2n-4.1991 Mathematics Subject Classification: 20C20, 20C33.     

Kamenev-type oscillation criteria for delay difference equations

Some oscillation criteria are established by Raccati transformation techniques for the following second-order nonlinear neutral difference equation Δ(pn(Δ(xn cnxn-τ))γ) qnxβn-σ=0,n=0,1,2…which extend and include several oscillation criteria in [11], and also correct a theorem and its proof in [10].     

Deformation Theory and The Computation of Zeta Functions

We present a new approach to the problem of computing the zetafunction of a hypersurface over a finite field. For a hypersurfacedefined by a polynomial of degree d in n variables over thefield of q elements, one desires an algorithm whose runningtime is a polynomial function of dⁿ log(q). (Here we assumed 2, for otherwise the problem is easy.) The case n = 1 isrelated to univariate polynomial factorisation and is comparativelystraightforward. When n = 2 one is counting points on curves,and the method of Schoof and Pila yields a complexity of , where the function C_d depends exponentiallyon d. For arbitrary n, the theorem of the author and Wan givesa complexity which is a polynomial function of (pdⁿ log(q))ⁿ,where p is the characteristic of the field. A complexity estimateof this form can also be achieved for smooth hypersurfaces usingthe method of Kedlaya, although this has only been worked outin full for curves. The new approach we present should yielda complexity which is a small polynomial function of pdⁿ log(q).In this paper, we work this out in full for Artin–Schreierhypersurfaces defined by equations of the form Z^p – Z= f, where the polynomial f has a diagonal leading form. Themethod utilises a relative p-adic cohomology theory for familiesof hypersurfaces, due in essence to Dwork. As a corollary ofour main theorem, we obtain the following curious result. Letf be a multivariate polynomial with integer coefficients whoseleading form is diagonal. There exists an explicit deterministicalgorithm which takes as input a prime p, outputs the numberof solutions to the congruence equation f = 0 op, and runs in bit operations, for any >0. This improves upon the elementary estimate of bit operations, where n is the number of variables,which can be achieved using Berlekamp's root counting algorithm.2000 Mathematics Subject Classification 11Y99, 11M38, 11T99.