1. CMB Online first
2. CMB Online first
 González, José Luis; Karu, Kalle

Examples of nonfinitely generated Cox rings
We bring examples of toric varieties blown up at a point in the torus that do not have finitely generated Cox rings. These examples are generalizations of
our earlier work,
where toric surfaces of Picard number $1$ were studied. In this article we consider toric varieties of higher Picard number and higher dimension. In particular, we bring examples of weighted projective $3$spaces blown up at a point that do not have finitely generated Cox rings.
Keywords:Cox ring, Mori dream space, toric variety Categories:14M25, 14C20, 14E30 

3. CMB 2018 (vol 61 pp. 836)
 Purbhoo, Kevin

Total Nonnegativity and Stable Polynomials
We consider homogeneous multiaffine polynomials whose coefficients
are the PlÃ¼cker coordinates of a point $V$ of the Grassmannian.
We show that such a polynomial is stable (with respect to the
upper half plane) if and only if $V$ is in the totally nonnegative
part of the Grassmannian. To prove this, we consider an action
of
matrices on multiaffine polynomials. We show that
a matrix $A$ preserves stability of polynomials if and only if
$A$ is totally nonnegative. The proofs are applications of classical
theory of totally nonnegative matrices, and the generalized
PÃ³lyaSchur theory of Borcea and BrÃ¤ndÃ©n.
Keywords:stable polynomial, zeros of a complex polynomial, total nonnegative Grassmannian, totally nonnegative matrix Categories:32A60, 14M15, 14P10, 15B48 

4. CMB Online first
 Asgarli, Shamil

Sharp Bertini theorem for plane curves over finite fields
We prove that if $C$ is a reflexive smooth plane curve of degree
$d$ defined over a finite field $\mathbb{F}_q$ with $d\leq q+1$, then
there is an $\mathbb{F}_q$line $L$ that intersects $C$ transversely.
We also prove the same result for nonreflexive curves of degree
$p+1$ and $2p+1$ where $q=p^{r}$.
Keywords:Bertini theorem, transversality, finite field Categories:14H50, 11G20, 14N05 

5. CMB 2018 (vol 61 pp. 878)
6. CMB Online first
 Bertapelle, A.; Mazzari, N.

On deformations of $1$motives
According to a wellknown theorem of Serre and Tate, the infinitesimal
deformation theory of an abelian variety in positive characteristic
is equivalent to the infinitesimal deformation theory of its
BarsottiTate group. We extend this result to $1$motives.
Keywords:$1$motive, BarsottiTate group Categories:14L15, 14C15, 14L05 

7. CMB Online first
 Zhang, Zheng

On motivic realizations of the canonical Hermitian variations of Hodge structure of CalabiYau type over type $D^{\mathbb H}$ domains
Let $\mathcal{D}$ be the irreducible Hermitian symmetric domain
of type $D_{2n}^{\mathbb{H}}$. There exists a canonical Hermitian
variation of real Hodge structure $\mathcal{V}_{\mathbb{R}}$
of CalabiYau type over $\mathcal{D}$. This short note concerns
the problem of giving motivic realizations for $\mathcal{V}_{\mathbb{R}}$.
Namely, we specify a descent of $\mathcal{V}_{\mathbb{R}}$ from
$\mathbb{R}$ to $\mathbb{Q}$ and ask whether the $\mathbb{Q}$descent
of $\mathcal{V}_{\mathbb{R}}$ can be realized as subvariation
of rational Hodge structure of those coming from families of
algebraic varieties. When $n=2$, we give a motivic realization
for $\mathcal{V}_{\mathbb{R}}$. When $n \geq 3$, we show that
the unique irreducible factor of CalabiYau type in $\mathrm{Sym}^2
\mathcal{V}_{\mathbb{R}}$ can be realized motivically.
Keywords:variations of Hodge structure, Hermitian symmetric domain Categories:14D07, 32G20, 32M15 

8. CMB 2017 (vol 61 pp. 659)
9. CMB 2017 (vol 61 pp. 650)
 Shirane, Taketo

Connected numbers and the embedded topology of plane curves
The splitting number of a plane irreducible curve for a Galois
cover is effective to distinguish the embedded topology of plane
curves.
In this paper, we define the connected number of a plane
curve (possibly reducible) for a Galois cover, which is similar
to the splitting number.
By using the connected number, we distinguish the embedded topology
of Artal arrangements of degree $b\geq 4$, where an Artal arrangement
of degree $b$ is a plane curve consisting of one smooth curve
of degree $b$ and three of its total inflectional tangen
Keywords:plane curve, splitting curve, Zariski pair, cyclic cover, splitting number Categories:14H30, 14H50, 14F45 

10. CMB Online first
 Reichstein, Zinovy B.

On a property of real plane curves of even degree
F. Cukierman asked whether or not for every
smooth
real plane curve $X \subset \mathbb{P}^2$ of even degree $d \geqslant
2$
there exists a real line
$L \subset \mathbb{P}^2$ such $X \cap L$ has no real points.
We show that the answer is ``yes" if $d = 2$ or $4$ and ``no"
if $n \geqslant 6$.
Keywords:real algebraic geometry, plane curve, maximizer function, bitangent Categories:14P05, 14H50 

11. CMB 2017 (vol 61 pp. 572)
 Koskivirta, JeanStefan

Normalization of closed EkedahlOort strata
We apply our theory of partial flag spaces developed
with W. Goldring
to study a grouptheoretical generalization of the canonical
filtration of a truncated BarsottiTate group of level 1. As
an application, we determine explicitly the normalization of
the Zariski closures of EkedahlOort strata of Shimura varieties
of Hodgetype as certain closed coarse strata in the associated
partial flag spaces.
Keywords:EkedahlOort stratification, Shimura variety Categories:14K10, 20G40, 11G18 

12. CMB 2017 (vol 61 pp. 608)
13. CMB 2017 (vol 61 pp. 328)
 Maican, Mario

Moduli of Space Sheaves with Hilbert Polynomial $4m+1$
We investigate the moduli space of sheaves supported on space
curves of degree $4$ and having Euler characteristic $1$.
We give an elementary proof of the fact that this moduli space
consists of three irreducible components.
Keywords:moduli of sheaves, semistable sheaves Categories:14D20, 14D22 

14. CMB 2017 (vol 61 pp. 272)
 Franz, Matthias

Symmetric Products of Equivariantly Formal Spaces
Let \(X\) be a CW complex with a continuous action of a topological
group \(G\).
We show that if \(X\) is equivariantly formal for singular
cohomology
with coefficients in some field \(\Bbbk\), then so are all symmetric
products of \(X\)
and in fact all its \(\Gamma\)products.
In particular, symmetric products
of quasiprojective Mvarieties are again Mvarieties.
This generalizes a result by Biswas and D'Mello
about symmetric products of Mcurves.
We also discuss several related questions.
Keywords:symmetric product, equivariant formality, maximal variety, Gamma product Categories:55N91, 55S15, 14P25 

15. CMB 2017 (vol 60 pp. 490)
 Fiori, Andrew

A RiemannHurwitz Theorem for the Algebraic Euler Characteristic
We prove an analogue of the RiemannHurwitz theorem for computing
Euler characteristics of pullbacks of coherent sheaves through
finite maps of smooth projective varieties in arbitrary dimensions,
subject only to the condition that the irreducible components
of the branch and ramification locus have simple normal crossings.
Keywords:RiemannHurwitz, logarithmicChern class, Euler characteristic Categories:14F05, 14C17 

16. CMB 2017 (vol 61 pp. 201)
 Takahashi, Tomokuni

Projective plane bundles over an elliptic curve
We calculate the dimension of cohomology groups for
the holomorphic tangent bundles of each isomorphism
class of the projective plane bundle over an elliptic curve.
As an application, we construct the families
of projective plane bundles, and prove that the families
are effectively parametrized and complete.
Keywords:projective plane bundle, vector bundle, elliptic curve, deformation, KodairaSpencer map Categories:14J10, 14J30, 14D15 

17. CMB 2017 (vol 60 pp. 478)
 Carrell, Jim; Kaveh, Kiumars

Springer's Weyl Group Representation via Localization
Let $G$ denote a reductive algebraic group over
$\mathbb{C}$
and $x$ a nilpotent element of its Lie algebra $\mathfrak{g}$. The Springer
variety $\mathcal{B}_x$
is the closed subvariety of the flag variety $\mathcal{B}$ of $G$ parameterizing
the
Borel subalgebras of $\mathfrak{g}$ containing $x$. It has the remarkable
property that
the Weyl group $W$ of $G$ admits a representation on the cohomology
of $\mathcal{B}_x$
even though $W$ rarely acts on $\mathcal{B}_x$ itself. Wellknown constructions
of this action
due to Springer et al use technical machinery from algebraic
geometry.
The purpose of this note is to describe an elementary approach
that gives this action
when $x$ is what we call parabolicsurjective. The idea is to
use localization to construct an action of $W$ on
the equivariant cohomology algebra $H_S^*(\mathcal{B}_x)$, where $S$ is a certain algebraic
subtorus of $G$.
This action descends to $H^*(\mathcal{B}_x)$ via the forgetful map and
gives the desired representation. The parabolicsurjective case
includes all nilpotents of type $A$ and,
more generally, all nilpotents for which it is known that $W$
acts on
$H_S^*(\mathcal{B}_x)$ for some torus $S$.
Our result is deduced from a general theorem describing
when a group action on the cohomology of the fixed point set of a
torus action
on a space lifts to the full cohomology algebra of the space.
Keywords:Springer variety, Weyl group action, equivariant cohomology Categories:14M15, 14F43, 55N91 

18. CMB 2017 (vol 60 pp. 747)
 Huang, Yanhe; Sottile, Frank; Zelenko, Igor

Injectivity of Generalized Wronski Maps
We study linear projections on PlÃ¼cker space whose restriction
to the Grassmannian is a nontrivial branched
cover.
When an automorphism of the Grassmannian preserves the fibers,
we show that the Grassmannian is necessarily
of $m$dimensional linear subspaces in a symplectic vector
space of dimension $2m$, and the linear map is
the Lagrangian involution.
The Wronski map for a selfadjoint linear differential operator
and pole placement map for
symmetric linear systems are natural examples.
Keywords:Wronski map, PlÃ¼cker embedding, curves in Lagrangian Grassmannian, selfadjoint linear differential operator, symmetric linear control system, pole placement map Categories:14M15, 34A30, 93B55 

19. CMB 2017 (vol 60 pp. 309)
20. CMB 2017 (vol 60 pp. 225)
 Bahmanpour, Kamal; Naghipour, Reza

Faltings' Finiteness Dimension of Local Cohomology Modules Over Local CohenMacaulay Rings
Let $(R, \frak m)$ denote a local CohenMacaulay ring and $I$
a nonnilpotent ideal of $R$. The purpose of this article is
to investigate Faltings' finiteness
dimension $f_I(R)$ and equidimensionalness of certain homomorphic
image of $R$. As a consequence
we deduce that $f_I(R)=\operatorname{max}\{1, \operatorname{ht} I\}$
and if $\operatorname{mAss}_R(R/I)$
is contained in $\operatorname{Ass}_R(R)$, then the ring $R/ I+\cup_{n\geq
1}(0:_RI^n)$ is equidimensional of dimension $\dim R1$.
Moreover, we will obtain a lower bound for injective dimension
of the local cohomology module $H^{\operatorname{ht} I}_I(R)$, in the case
$(R, \frak m)$ is a complete equidimensional local ring.
Keywords:Cohen Macaulay ring, equidimensional ring, finiteness dimension, local cohomology Categories:13D45, 14B15 

21. CMB 2017 (vol 61 pp. 166)
 MirandaNeto, Cleto B.

A moduletheoretic characterization of algebraic hypersurfaces
In this note we prove the following surprising characterization:
if
$X\subset {\mathbb A}^n$ is an (embedded, nonempty, proper)
algebraic variety defined over a
field $k$ of characteristic zero, then $X$ is a hypersurface
if and only if the module $T_{{\mathcal O}_{{\mathbb
A}^n}/k}(X)$ of logarithmic vector fields of
$X$ is a reflexive ${\mathcal
O}_{{\mathbb A}^n}$module. As a consequence of this result,
we derive that if $T_{{\mathcal O}_{{\mathbb A}^n}/k}(X)$ is a
free ${\mathcal
O}_{{\mathbb A}^n}$module, which is shown to be equivalent
to the freeness of the $t$th exterior power of $T_{{\mathcal O}_{{\mathbb
A}^n}/k}(X)$ for some (in fact, any) $t\leq n$, then necessarily
$X$ is a Saito free divisor.
Keywords:hypersurface, logarithmic vector field, logarithmic derivation, free divisor Categories:14J70, 13N15, 32S22, 13C05, 13C10, 14N20, , , , , 14C20, 32M25 

22. CMB 2017 (vol 60 pp. 329)
 Le Fourn, Samuel

Nonvanishing of Central Values of $L$functions of Newforms in $S_2 (\Gamma_0 (dp^2))$ Twisted by Quadratic Characters
We prove that for $d \in \{ 2,3,5,7,13 \}$ and $K$ a quadratic
(or rational) field of discriminant $D$ and Dirichlet character
$\chi$, if a prime $p$ is large enough compared to $D$, there
is a newform $f \in S_2(\Gamma_0(dp^2))$ with sign $(+1)$ with
respect to the AtkinLehner involution $w_{p^2}$ such that $L(f
\otimes \chi,1) \neq 0$. This result is obtained through an estimate
of a weighted sum of twists of $L$functions which generalises
a result of Ellenberg. It relies on the approximate functional
equation for the $L$functions $L(f \otimes \chi, \cdot)$ and
a Petersson trace formula restricted to AtkinLehner eigenspaces.
An application of this nonvanishing theorem will be given in
terms of existence of rank zero quotients of some twisted jacobians,
which generalises a result of Darmon and Merel.
Keywords:nonvanishing of $L$functions of modular forms, Petersson trace formula, rank zero quotients of jacobians Categories:14J15, 11F67 

23. CMB 2016 (vol 60 pp. 510)
 Haase, Christian; Hofmann, Jan

Convexnormal (Pairs of) Polytopes
In 2012 Gubeladze (Adv. Math. 2012)
introduced the notion of $k$convexnormal polytopes to show
that
integral polytopes all of whose edges are longer than $4d(d+1)$
have
the integer decomposition property.
In the first part of this paper we show that for lattice polytopes
there is no difference between $k$ and $(k+1)$convexnormality
(for
$k\geq 3 $) and improve the bound to $2d(d+1)$. In the second
part we
extend the definition to pairs of polytopes. Given two rational
polytopes $P$ and $Q$, where the normal fan of $P$ is a refinement
of
the normal fan of $Q$.
If every edge $e_P$ of $P$ is at least $d$ times as long as the
corresponding face (edge or vertex) $e_Q$ of $Q$, then $(P+Q)\cap
\mathbb{Z}^d
= (P\cap \mathbb{Z}^d ) + (Q \cap \mathbb{Z}^d)$.
Keywords:integer decomposition property, integrally closed, projectively normal, lattice polytopes Categories:52B20, 14M25, 90C10 

24. CMB 2016 (vol 60 pp. 613)
 Reichstein, Zinovy; Vistoli, Angelo

On the Dimension of the Locus of Determinantal Hypersurfaces
The characteristic polynomial $P_A(x_0, \dots,
x_r)$
of an $r$tuple $A := (A_1, \dots, A_r)$ of $n \times n$matrices
is
defined as
\[ P_A(x_0, \dots, x_r) := \det(x_0 I + x_1 A_1 + \dots + x_r
A_r) \, . \]
We show that if $r \geqslant 3$
and $A := (A_1, \dots, A_r)$ is an $r$tuple of $n \times n$matrices in general position,
then up to conjugacy, there are only finitely many $r$tuples
$A' := (A_1', \dots, A_r')$ such that $p_A = p_{A'}$. Equivalently,
the locus of determinantal hypersurfaces of degree $n$ in $\mathbf{P}^r$
is irreducible of dimension $(r1)n^2 + 1$.
Keywords:determinantal hypersurface, matrix invariant, $q$binomial coefficient Categories:14M12, 15A22, 05A10 

25. CMB 2016 (vol 59 pp. 865)
 Pal, Sarbeswar

Moduli of Rank 2 Stable Bundles and Hecke Curves
Let $X$ be smooth projective curve of arbitrary genus $g \gt 3$
over complex numbers. In this short note we will show that the
moduli
space of rank $2$ stable vector bundles with determinant isomorphic
to $L_x$, where $L_x$ denote the line bundle corresponding to
a point $x \in X$ is isomorphic to certain lines in the moduli
space of Sequivalence classes of semistable bundles of rank
2 with
trivial determinant.
Keywords:Hecke curve, (0,1) stable bundle Category:14D21 
