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101. CMB 2007 (vol 50 pp. 196)

Fernández, Julio; González, Josep; Lario, Joan-C.
Plane Quartic Twists of $X(5,3)$
Given an odd surjective Galois representation $\varrho\from \G_\Q\to\PGL_2(\F_3)$ and a positive integer~$N$, there exists a twisted modular curve $X(N,3)_\varrho$ defined over $\Q$ whose rational points classify the quadratic $\Q$-curves of degree $N$ realizing~$\varrho$. This paper gives a method to provide an explicit plane quartic model for this curve in the genus-three case $N=5$.

Categories:11F03, 11F80, 14G05

102. CMB 2007 (vol 50 pp. 284)

McIntosh, Richard J.
Second Order Mock Theta Functions
In his last letter to Hardy, Ramanujan defined 17 functions $F(q)$, where $|q|<1$. He called them mock theta functions, because as $q$ radially approaches any point $e^{2\pi ir}$ ($r$ rational), there is a theta function $F_r(q)$ with $F(q)-F_r(q)=O(1)$. In this paper we establish the relationship between two families of mock theta functions.

Keywords:$q$-series, mock theta function, Mordell integral
Categories:11B65, 33D15

103. CMB 2007 (vol 50 pp. 71)

Gurak, S.
Polynomials for Kloosterman Sums
Fix an integer $m>1$, and set $\zeta_{m}=\exp(2\pi i/m)$. Let ${\bar x}$ denote the multiplicative inverse of $x$ modulo $m$. The Kloosterman sums $R(d)=\sum_{x} \zeta_{m}^{x + d{\bar x}}$, $1 \leq d \leq m$, $(d,m)=1$, satisfy the polynomial $$f_{m}(x) = \prod_{d} (x-R(d)) = x^{\phi(m)} +c_{1} x^{\phi(m)-1} + \dots + c_{\phi(m)},$$ where the sum and product are taken over a complete system of reduced residues modulo $m$. Here we give a natural factorization of $f_{m}(x)$, namely, $$ f_{m}(x) = \prod_{\sigma} f_{m}^{(\sigma)}(x),$$ where $\sigma$ runs through the square classes of the group ${\bf Z}_{m}^{*}$ of reduced residues modulo $m$. Questions concerning the explicit determination of the factors $f_{m}^{(\sigma)}(x)$ (or at least their beginning coefficients), their reducibility over the rational field ${\bf Q}$ and duplication among the factors are studied. The treatment is similar to what has been done for period polynomials for finite fields.

Categories:11L05, 11T24

104. CMB 2007 (vol 50 pp. 158)

Tipu, Vicentiu
A Note on Giuga's Conjecture
Let $G(X)$ denote the number of positive composite integers $n$ satisfying $\sum_{j=1}^{n-1}j^{n-1}\equiv -1 \tmod{n}$. Then $G(X)\ll X^{1/2}\log X$ for sufficiently large $X$.

Category:11A51

105. CMB 2007 (vol 50 pp. 11)

Borwein, David; Borwein, Jonathan
van der Pol Expansions of L-Series
We provide concise series representations for various L-series integrals. Different techniques are needed below and above the abscissa of absolute convergence of the underlying L-series.

Keywords:Dirichlet series integrals, Hurwitz zeta functions, Plancherel theorems, L-series
Categories:11M35, 11M41, 30B50

106. CMB 2006 (vol 49 pp. 578)

Muić, Goran
On the Structure of the Full Lift for the Howe Correspondence of $(Sp(n), O(V))$ for Rank-One Reducibilities
In this paper we determine the structure of the full lift for the Howe correspondence of $(Sp(n),O(V))$ for rank-one reducibilities.

Categories:22E35, 22E50, 11F70

107. CMB 2006 (vol 49 pp. 560)

Luijk, Ronald van
A K3 Surface Associated With Certain Integral Matrices Having Integral Eigenvalues
In this article we will show that there are infinitely many symmetric, integral $3 \times 3$ matrices, with zeros on the diagonal, whose eigenvalues are all integral. We will do this by proving that the rational points on a certain non-Kummer, singular K3 surface are dense. We will also compute the entire Néron-Severi group of this surface and find all low degree curves on it.

Keywords:symmetric matrices, eigenvalues, elliptic surfaces, K3 surfaces, Néron--Severi group, rational curves, Diophantine equations, arithmetic geometry, algebraic geometry, number theory
Categories:14G05, 14J28, 11D41

108. CMB 2006 (vol 49 pp. 481)

Browkin, J.; Brzeziński, J.
On Sequences of Squares with Constant Second Differences
The aim of this paper is to study sequences of integers for which the second differences between their squares are constant. We show that there are infinitely many nontrivial monotone sextuples having this property and discuss some related problems.

Keywords:sequence of squares, second difference, elliptic curve
Categories:11B83, 11Y85, 11D09

109. CMB 2006 (vol 49 pp. 526)

Choi, So Young
The Values of Modular Functions and Modular Forms
Let $\Gamma_0$ be a Fuchsian group of the first kind of genus zero and $\Gamma$ be a subgroup of $\Gamma_0$ of finite index of genus zero. We find universal recursive relations giving the $q_{r}$-series coefficients of $j_0$ by using those of the $q_{h_{s}}$-series of $j$, where $j$ is the canonical Hauptmodul for $\Gamma$ and $j_0$ is a Hauptmodul for $\Gamma_0$ without zeros on the complex upper half plane $\mathfrak{H}$ (here $q_{\ell} := e^{2 \pi i z / \ell}$). We find universal recursive formulas for $q$-series coefficients of any modular form on $\Gamma_0^{+}(p)$ in terms of those of the canonical Hauptmodul $j_p^{+}$.

Categories:10D12, 11F11

110. CMB 2006 (vol 49 pp. 472)

Silvester, Alan K.; Spearman, Blair K.; Williams, Kenneth S.
Cyclic Cubic Fields of Given Conductor and Given Index
The number of cyclic cubic fields with a given conductor and a given index is determined.

Keywords:Discriminant, conductor, index, cyclic cubic field
Categories:11R16, 11R29

111. CMB 2006 (vol 49 pp. 428)

Lee, Min Ho
Vector-Valued Modular Forms of Weight Two Associated With Jacobi-Like Forms
We construct vector-valued modular forms of weight 2 associated to Jacobi-like forms with respect to a symmetric tensor representation of $\G$ by using the method of Kuga and Shimura as well as the correspondence between Jacobi-like forms and sequences of modular forms. As an application, we obtain vector-valued modular forms determined by theta functions and by pseudodifferential operators.

Categories:11F11, 11F50

112. CMB 2006 (vol 49 pp. 448)

Pacelli, Allison M.
A Lower Bound on the Number of Cyclic Function Fields With Class Number Divisible by $n$
In this paper, we find a lower bound on the number of cyclic function fields of prime degree~$l$ whose class numbers are divisible by a given integer $n$. This generalizes a previous result of D. Cardon and R. Murty which gives a lower bound on the number of quadratic function fields with class numbers divisible by $n$.

Categories:11R29, 11R58

113. CMB 2006 (vol 49 pp. 296)

Sch"utt, Matthias
On the Modularity of Three Calabi--Yau Threefolds With Bad Reduction at 11
This paper investigates the modularity of three non-rigid Calabi--Yau threefolds with bad reduction at 11. They are constructed as fibre products of rational elliptic surfaces, involving the modular elliptic surface of level 5. Their middle $\ell$-adic cohomology groups are shown to split into two-dimensional pieces, all but one of which can be interpreted in terms of elliptic curves. The remaining pieces are associated to newforms of weight 4 and level 22 or 55, respectively. For this purpose, we develop a method by Serre to compare the corresponding two-dimensional 2-adic Galois representations with uneven trace. Eventually this method is also applied to a self fibre product of the Hesse-pencil, relating it to a newform of weight 4 and level 27.

Categories:14J32, 11F11, 11F23, 20C12

114. CMB 2006 (vol 49 pp. 247)

Myjak, Józef; Szarek, Tomasz; Ślȩczka, Maciej
A Szpilrajn--Marczewski Type Theorem for Concentration Dimension on Polish Spaces
Let $X$ be a Polish space. We will prove that $$ \dim_T X=\inf \{\dim_L X': X'\text{ is homeomorphic to } X\}, $$ where $\dim_L X$ and $\dim_T X$ stand for the concentration dimension and the topological dimension of $X$, respectively.

Keywords:Hausdorff dimension, topological dimension, Lévy concentration function, concentration dimension
Categories:11K55, 28A78

115. CMB 2006 (vol 49 pp. 196)

Chernousov, Vladimir
Another Proof of Totaro's Theorem on $E_8$-Torsors
We give a short proof of Totaro's theorem that every$E_8$-torsor over a field $k$ becomes trivial over a finiteseparable extension of $k$of degree dividing $d(E_8)=2^63^25$.

Categories:11E72, 14M17, 20G15

116. CMB 2006 (vol 49 pp. 21)

Chapman, Robin; Hart, William
Evaluation of the Dedekind Eta Function
We extend the methods of Van der Poorten and Chapman for explicitly evaluating the Dede\-kind eta function at quadratic irrationalities. Via evaluation of Hecke $L$-series we obtain new evaluations at points in imaginary quadratic number fields with class numbers 3 and 4. Further, we overcome the limitations of the earlier methods and via modular equations provide explicit evaluations where the class number is 5 or 7.

Category:11G15

117. CMB 2006 (vol 49 pp. 108)

Kwapisz, Jaroslaw
A Dynamical Proof of Pisot's Theorem
We give a geometric proof of classical results that characterize Pisot numbers as algebraic $\lambda>1$ for which there is $x\neq0$ with $\lambda^nx \to 0 \mod$ and identify such $x$ as members of $\Z[\lambda^{-1}] \cdot \Z[\lambda]^*$ where $\Z[\lambda]^*$ is the dual module of $\Z[\lambda]$.

Category:11R06

118. CMB 2005 (vol 48 pp. 576)

Ichimura, Humio
On a Theorem of Kawamoto on Normal Bases of Rings of Integers, II
Let $m=p^e$ be a power of a prime number $p$. We say that a number field $F$ satisfies the property $(H_m')$ when for any $a \in F^{\times}$, the cyclic extension $F(\z_m, a^{1/m})/F(\z_m)$ has a normal $p$-integral basis. We prove that $F$ satisfies $(H_m')$ if and only if the natural homomorphism $Cl_F' \to Cl_K'$ is trivial. Here $K=F(\zeta_m)$, and $Cl_F'$ denotes the ideal class group of $F$ with respect to the $p$-integer ring of $F$.

Category:11R33

119. CMB 2005 (vol 48 pp. 535)

Ellenberg, Jordan S.
On the Error Term in Duke's Estimate for the Average Special Value of $L$-Functions
Let $\FF$ be an orthonormal basis for weight $2$ cusp forms of level $N$. We show that various weighted averages of special values $L(f \tensor \chi, 1)$ over $f \in \FF$ are equal to $4 \pi c + O(N^{-1 + \epsilon})$, where $c$ is an explicit nonzero constant. A previous result of Duke gives an error term of $O(N^{-1/2}\log N)$.

Categories:11F67, 11F11

120. CMB 2005 (vol 48 pp. 636)

Győry, K.; Hajdu, L.; Saradha, N.
Correction to: On the Diophantine Equation $n(n+d)\cdots(n+(k-1)d)=by^l$
In the article under consideration (Canad. Math. Bull. \textbf{47} (2004), pp.~373--388), Lemma 6 is not true in the form presented there. Lemma 6 is used only in the proof of part (i) of Theorem 9. We note, however, that part (i) of Theorem 9 in question is a special case of a theorem by Bennet, Bruin, Gy\H{o}ry and Hajdu.

Category:11D41

121. CMB 2005 (vol 48 pp. 333)

Alzer, Horst
Monotonicity Properties of the Hurwitz Zeta Function
Let $$ \zeta(s,x)=\sum_{n=0}^{\infty}\frac{1}{(n+x)^s} \quad{(s>1,\, x>0)} $$ be the Hurwitz zeta function and let $$ Q(x)=Q(x;\alpha,\beta;a,b)=\frac{(\zeta(\alpha,x))^a}{(\zeta(\beta,x))^b}, $$ where $\alpha, \beta>1$ and $a,b>0$ are real numbers. We prove: (i) The function $Q$ is decreasing on $(0,\infty)$ if{}f $\alpha a-\beta b\geq \max(a-b,0)$. (ii) $Q$ is increasing on $(0,\infty)$ if{}f $\alpha a-\beta b\leq \min(a-b,0)$. An application of part (i) reveals that for all $x>0$ the function $s\mapsto [(s-1)\zeta(s,x)]^{1/(s-1)}$ is decreasing on $(1,\infty)$. This settles a conjecture of Bastien and Rogalski.

Categories:11M35, 26D15

122. CMB 2005 (vol 48 pp. 394)

Đoković, D. Ž.; Szechtman, F.; Zhao, K.
Diagonal Plus Tridiagonal Representatives for Symplectic Congruence Classes of Symmetric Matrices
Let $n=2m$ be even and denote by $\Sp_n(F)$ the symplectic group of rank $m$ over an infinite field $F$ of characteristic different from $2$. We show that any $n\times n$ symmetric matrix $A$ is equivalent under symplectic congruence transformations to the direct sum of $m\times m$ matrices $B$ and $C$, with $B$ diagonal and $C$ tridiagonal. Since the $\Sp_n(F)$-module of symmetric $n\times n$ matrices over $F$ is isomorphic to the adjoint module $\sp_n(F)$, we infer that any adjoint orbit of $\Sp_n(F)$ in $\sp_n(F)$ has a representative in the sum of $3m-1$ root spaces, which we explicitly determine.

Categories:11E39, 15A63, 17B20

123. CMB 2005 (vol 48 pp. 428)

Miyamoto, Roland; Top, Jaap
Reduction of Elliptic Curves in Equal Characteristic~3 (and~2)
and fibre type for elliptic curves over discrete valued fields of equal characteristic~3. Along the same lines, partial results are obtained in equal characteristic~2.

Categories:14H52, 14K15, 11G07, 11G05, 12J10

124. CMB 2005 (vol 48 pp. 211)

Germain, Jam
The Distribution of Totatives
The integers coprime to $n$ are called the {\it totatives} \rm of $n$. D. H. Lehmer and Paul Erd\H{o}s were interested in understanding when the number of totatives between $in/k$ and $(i+1)n/k$ are $1/k$th of the total number of totatives up to $n$. They provided criteria in various cases. Here we give an ``if and only if'' criterion which allows us to recover most of the previous results in this literature and to go beyond, as well to reformulate the problem in terms of combinatorial group theory. Our criterion is that the above holds if and only if for every odd character $\chi \pmod \kappa$ (where $\kappa:=k/\gcd(k,n/\prod_{p|n} p)$) there exists a prime $p=p_\chi$ dividing $n$ for which $\chi(p)=1$.

Categories:11A05, 11A07, 11A25, 20C99

125. CMB 2005 (vol 48 pp. 16)

Cojocaru, Alina Carmen
On the Surjectivity of the Galois Representations Associated to Non-CM Elliptic Curves
Let $ E $ be an elliptic curve defined over $\Q,$ of conductor $N$ and without complex multiplication. For any positive integer $l$, let $\phi_l$ be the Galois representation associated to the $l$-division points of~$E$. From a celebrated 1972 result of Serre we know that $\phi_l$ is surjective for any sufficiently large prime $l$. In this paper we find conditional and unconditional upper bounds in terms of $N$ for the primes $l$ for which $\phi_l$ is {\emph{not}} surjective.

Categories:11G05, 11N36, 11R45
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