76. CMB 2006 (vol 49 pp. 464)
 Ravindra, G. V.

A Note on Detecting Algebraic Cycles
The purpose of this note is to show that the homologically trivial
cycles contructed by Clemens and their generalisations
due to Paranjape can be detected by the technique of
spreading out. More precisely, we associate to these cycles (and the
ambient varieties in which they live) certain families which arise
naturally and which are defined over $\bbC$ and show that these
cycles, along with their relations, can be detected in the singular
cohomology of the total space of these families.
Category:14C25 

77. CMB 2006 (vol 49 pp. 270)
78. CMB 2006 (vol 49 pp. 296)
 Sch"utt, Matthias

On the Modularity of Three CalabiYau Threefolds With Bad Reduction at 11
This paper investigates the modularity of three
nonrigid CalabiYau 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
twodimensional 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
twodimensional 2adic Galois representations with uneven trace.
Eventually this method is also applied to a self fibre product of
the Hessepencil, relating it to a newform of weight 4 and level
27.
Categories:14J32, 11F11, 11F23, 20C12 

79. CMB 2006 (vol 49 pp. 196)
80. CMB 2006 (vol 49 pp. 72)
 Dwilewicz, Roman J.

Additive RiemannHilbert Problem in Line Bundles Over $\mathbb{CP}^1$
In this note we consider $\overline\partial$problem in
line bundles over complex projective space $\mathbb{CP}^1$
and prove that the
equation can be solved for $(0,1)$ forms with compact support. As a
consequence, any CauchyRiemann function on a compact real hypersurface in
such line bundles is a jump of two holomorphic functions defined on the
sides of the hypersurface. In particular, the results can be applied to
$\mathbb{CP}^2$ since by removing a point from it we get a line bundle over
$\mathbb{CP}^1$.
Keywords:$\overline\partial$problem, cohomology groups, line bundles Categories:32F20, 14F05, 32C16 

81. CMB 2006 (vol 49 pp. 11)
 Bevelacqua, Anthony J.; Motley, Mark J.

GoingDown Results for $C_{i}$Fields
We search for theorems that, given a $C_i$field $K$ and a subfield $k$ of $K$, allow
us to conclude that $k$ is a $C_j$field for some $j$. We give appropriate theorems in
the case $K=k(t)$ and $K = k\llp t\rrp$. We then consider the more difficult case where $K/k$
is an algebraic extension. Here we are able to prove some results, and make conjectures. We
also point out the connection between these questions and Lang's conjecture on nonreal function
fields over a real closed field.
Keywords:$C_i$fields, Lang's Conjecture Categories:12F, 14G 

82. CMB 2005 (vol 48 pp. 622)
 Vénéreau, Stéphane

Hyperplanes of the Form ${f_1(x,y)z_1+\dots+f_k(x,y)z_k+g(x,y)}$ Are Variables
The AbhyankarSathaye Embedded Hyperplane Problem asks whe\ther any
hypersurface of $\C^n$ isomorphic to $\C^{n1}$ is rectifiable, {\em
i.e.,}
equivalent to a linear hyperplane up to an automorphism of $\C^n$.
Generalizing the approach adopted by Kaliman, V\'en\'ereau, and
Zaidenberg which
consists in using almost nothing but the acyclicity of $\C^{n1}$, we solve
this problem for hypersurfaces given by polynomials of $\C[x,y,z_1,\dots, z_k]$
as in the title.
Keywords:variables, AbhyankarSathaye Embedding Problem Categories:14R10, 14R25 

83. CMB 2005 (vol 48 pp. 547)
 Fehér, L. M.; Némethi, A.; Rimányi, R.

Degeneracy of 2Forms and 3Forms
We study some global aspects of differential complex 2forms and 3forms
on complex manifolds.
We compute the cohomology classes represented by the sets of points
on a manifold where such a form degenerates in various senses,
together with other similar cohomological obstructions.
Based on these results and a formula for projective
representations, we calculate the degree of the projectivization
of certain orbits of the representation $\Lambda^k\C^n$.
Keywords:Classes of degeneracy loci, 2forms, 3forms, Thom polynomials, global singularity theory Categories:14N10, 57R45 

84. CMB 2005 (vol 48 pp. 428)
85. CMB 2005 (vol 48 pp. 473)
86. CMB 2005 (vol 48 pp. 414)
 Kaveh, Kiumars

Vector Fields and the Cohomology Ring of Toric Varieties
Let $X$ be a smooth complex
projective variety with a holomorphic vector field with isolated
zero set $Z$. From the results of Carrell and Lieberman
there exists a filtration
$F_0 \subset F_1 \subset \cdots$ of $A(Z)$, the ring of
$\c$valued functions on $Z$, such that $\Gr A(Z) \cong H^*(X,
\c)$ as graded algebras. In this note, for a smooth projective
toric variety and a vector field generated by the action of a
$1$parameter subgroup of the torus, we work out this filtration.
Our main result is an explicit connection between this filtration
and the polytope algebra of $X$.
Keywords:Toric variety, torus action, cohomology ring, simple polytope,, polytope algebra Categories:14M25, 52B20 

87. CMB 2005 (vol 48 pp. 180)
 Cynk, Sławomir; Meyer, Christian

Geometry and Arithmetic of Certain Double Octic CalabiYau Manifolds
We study CalabiYau manifolds constructed as double coverings of
$\mathbb{P}^3$ branched along an octic surface. We give a list of 87
examples corresponding to arrangements of eight planes defined over
$\mathbb{Q}$. The Hodge numbers are computed for all examples. There are
10 rigid CalabiYau manifolds and 14 families with $h^{1,2}=1$. The
modularity conjecture is verified for all the rigid examples.
Keywords:CalabiYau, double coverings, modular forms Categories:14G10, 14J32 

88. CMB 2005 (vol 48 pp. 237)
 Kimura, Kenichiro

Indecomposable Higher Chow Cycles
Let $X$ be a projective smooth variety over a field $k$.
In the first part we show that
an indecomposable element in $CH^2(X,1)$ can be lifted
to an indecomposable element in $CH^3(X_K,2)$ where $K$ is the function
field of 1 variable over $k$. We also show that if $X$ is the selfproduct
of an elliptic curve over $\Q$ then the $\Q$vector space of
indecomposable cycles
$CH^3_{ind}(X_\C,2)_\Q$ is infinite dimensional.
In the second part we give a new
definition of the group of indecomposable cycles
of $CH^3(X,2)$ and give an example of nontorsion
cycle in this group.
Categories:14C25, 19D45 

89. CMB 2005 (vol 48 pp. 203)
90. CMB 2005 (vol 48 pp. 90)
 Jeffrey, Lisa C.; Mare, AugustinLiviu

Products of Conjugacy Classes in $SU(2)$
We obtain a complete description of the conjugacy classes
$C_1,\dots,C_n$ in $SU(2)$ with the property that $C_1\cdots
C_n=SU(2)$. The basic instrument is a characterization of the
conjugacy classes $C_1,\dots,C_{n+1}$ in $SU(2)$ with $C_1\cdots
C_{n+1}\ni I$, which generalizes a result of \cite{JeWe}.
Categories:14D20, 14P05 

91. CMB 2004 (vol 47 pp. 566)
 Koike, Kenji

Algebraicity of some Weil Hodge Classes
We show that the Prym map for 4th cyclic \'etale covers of curves
of genus 4 is a dominant morphism to a Shimura variety for a family
of Abelian 6folds of Weil type. According to the result of Schoen,
this implies algebraicity of Weil classes for this family.
Category:14C30 

92. CMB 2004 (vol 47 pp. 398)
 McKinnon, David

A Reduction of the BatyrevManin Conjecture for Kummer Surfaces
Let $V$ be a $K3$ surface defined over a number field $k$. The
BatyrevManin conjecture for $V$ states that for every nonempty open
subset $U$ of $V$, there exists a finite set $Z_U$ of accumulating
rational curves such that the density of rational points on $UZ_U$ is
strictly less than the density of rational points on $Z_U$. Thus,
the set of rational points of $V$ conjecturally admits a stratification
corresponding to the sets $Z_U$ for successively smaller sets $U$.
In this paper, in the case that $V$ is a Kummer surface, we prove that
the BatyrevManin conjecture for $V$ can be reduced to the
BatyrevManin conjecture for $V$ modulo the endomorphisms of $V$
induced by multiplication by $m$ on the associated abelian surface
$A$. As an application, we use this to show that given some restrictions
on $A$, the set of rational points of $V$ which lie on rational curves
whose preimages have geometric genus 2 admits a stratification of
Keywords:rational points, BatyrevManin conjecture, Kummer, surface, rational curve, abelian surface, height Categories:11G35, 14G05 

93. CMB 2004 (vol 47 pp. 264)
 McKinnon, David

Counting Rational Points on Ruled Varieties
In this paper, we prove a general result computing the number of rational points
of bounded height on a projective variety $V$ which is covered by lines. The
main technical result used to achieve this is an upper bound on the number of
rational points of bounded height on a line. This upper bound is such that it
can be easily controlled as the line varies, and hence is used to sum the counting
functions of the lines which cover the original variety $V$.
Categories:11G50, 11D45, 11D04, 14G05 

94. CMB 2004 (vol 47 pp. 271)
95. CMB 2004 (vol 47 pp. 22)
 Goto, Yasuhiro

A Note on the Height of the Formal Brauer Group of a $K3$ Surface
Using weighted Delsarte surfaces, we give examples of $K3$ surfaces
in positive characteristic whose formal Brauer groups have height
equal to $5$, $8$ or $9$. These are among the four values of the
height left open in the article of Yui \cite{Y}.
Keywords:formal Brauer groups, $K3$ surfaces in positive, characteristic, weighted Delsarte surfaces Categories:14L05, 14J28 

96. CMB 2003 (vol 46 pp. 546)
97. CMB 2003 (vol 46 pp. 575)
 Marshall, M.

Optimization of Polynomial Functions
This paper develops a refinement of Lasserre's algorithm for
optimizing a polynomial on a basic closed semialgebraic set via
semidefinite programming and addresses an open question concerning the
duality gap. It is shown that, under certain natural stability
assumptions, the problem of optimization on a basic closed set reduces
to the compact case.
Categories:14P10, 46L05, 90C22 

98. CMB 2003 (vol 46 pp. 495)
 Baragar, Arthur

Canonical Vector Heights on Algebraic K3 Surfaces with Picard Number Two
Let $V$ be an algebraic K3 surface defined over a number field $K$.
Suppose $V$ has Picard number two and an infinite group of
automorphisms $\mathcal{A} = \Aut(V/K)$. In this paper, we
introduce the notion of a vector height $\mathbf{h} \colon V \to
\Pic(V) \otimes \mathbb{R}$ and show the existence of a canonical
vector height $\widehat{\mathbf{h}}$ with the following properties:
\begin{gather*}
\widehat{\mathbf{h}} (\sigma P) = \sigma_* \widehat{\mathbf{h}} (P) \\
h_D (P) = \widehat{\mathbf{h}} (P) \cdot D + O(1),
\end{gather*}
where $\sigma \in \mathcal{A}$, $\sigma_*$ is the pushforward of
$\sigma$ (the pullback of $\sigma^{1}$), and $h_D$ is a Weil
height associated to the divisor $D$. The bounded function implied
by the $O(1)$ does not depend on $P$. This allows us to attack
some arithmetic problems. For example, we show that the number of
rational points with bounded logarithmic height in an
$\mathcal{A}$orbit satisfies
$$
N_{\mathcal{A}(P)} (t,D) = \# \{Q \in \mathcal{A}(P) : h_D (Q)
Categories:11G50, 14J28, 14G40, 14J50, 14G05 

99. CMB 2003 (vol 46 pp. 400)
 Marshall, M.

Approximating Positive Polynomials Using Sums of Squares
The paper considers the relationship between positive polynomials,
sums of squares and the multidimensional moment problem in the
general context of basic closed semialgebraic sets in real $n$space.
The emphasis is on the noncompact case and on quadratic module
representations as opposed to quadratic preordering presentations.
The paper clarifies the relationship between known results on the
algebraic side and on the functionalanalytic side and extends these
results in a variety of ways.
Categories:14P10, 44A60 

100. CMB 2003 (vol 46 pp. 429)
 Sastry, Pramathanath; Tong, Yue Lin L.

The Grothendieck Trace and the de Rham Integral
On a smooth $n$dimensional complete variety $X$ over ${\mathbb C}$ we
show that the trace map ${\tilde\theta}_X \colon\break
H^n (X,\Omega_X^n)
\to {\mathbb C}$ arising from Lipman's version of Grothendieck duality
in \cite{ast117} agrees with
$$
(2\pi i)^{n} (1)^{n(n1)/2} \int_X \colon H^{2n}_{DR} (X,{\mathbb
C}) \to {\mathbb C}
$$
under the Dolbeault isomorphism.
Categories:14F10, 32A25, 14A15, 14F05, 18E30 
