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| « 2007 (v59) | 2009 (v61) » |
Volume 60 (2008)
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| 3 | Convex Bodies of Minimal Volume, Surface Area and Mean Width with Respect to Thin Shells Böröczky, Károly; Böröczky, Károly J.; Schütt, Carsten; Wintsche, Gergely
Given $r>1$, we consider convex bodies in $\E^n$ which
contain a fixed unit ball, and whose
extreme points are of distance at least $r$ from the centre of
the unit ball, and we investigate how well these
convex bodies approximate the unit ball in terms of volume, surface area and
mean width. As $r$ tends to one, we prove asymptotic formulae
for the error of the approximation, and provide good estimates on
the involved constants depending on the dimension.
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| 33 | Higher Order Tangents to Analytic Varieties along Curves. II Braun, Rüdiger W.; Meise, Reinhold; Taylor, B. A.
Let~$V$ be an analytic variety in some open set in~$\C^n$. For a
real analytic curve~$\gamma$ with $ \gamma(0) = 0 $ and $ d \ge 1 $
define $ V_t = t^{-d}(V - \gamma(t)) $. It was shown in a previous
paper that the currents of integration over~$V_t$ converge to a
limit current whose support $ T_{\gamma,d} V $ is an algebraic
variety as~$t$ tends to zero. Here, it is shown that the canonical
defining function of the limit current is the suitably normalized
limit of the canonical defining functions of the~$V_t$. As a
corollary, it is shown that $ T_{\gamma,d} V $ is either
inhomogeneous or coincides with $ T_{\gamma,\delta} V $ for
all~$\delta$ in some neighborhood of~$d$. As another application it
is shown that for surfaces only a finite number of curves lead to
limit varieties that are interesting for the investigation of
Phragm\'en--Lindel\"of conditions. Corresponding results for limit
varieties $ T_{\sigma,\delta} W $ of algebraic varieties W along
real analytic curves tending to infinity are derived by a
reduction to the local case.
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| 64 | Classification of Linear Weighted Graphs Up to Blowing-Up and Blowing-Down Daigle, Daniel
We classify linear weighted graphs up to the
blowing-up and blowing-down operations which are relevant for the
study of algebraic surfaces.
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| 88 | Nilpotent Conjugacy Classes in $p$-adic Lie Algebras: The Odd Orthogonal Case Diwadkar, Jyotsna Mainkar
We will study the following question: Are nilpotent conjugacy
classes of reductive Lie algebras over $p$-adic fields
definable? By definable, we mean definable by a formula in Pas's
language. In this language, there are no field extensions and no
uniformisers. Using Waldspurger's parametrization, we answer in the
affirmative in the case of special orthogonal Lie algebras
$\mathfrak{so}(n)$ for $n$ odd, over $p$-adic fields.
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| 109 | Affine Lines on Affine Surfaces and the Makar--Limanov Invariant Gurjar, R. V.; Masuda, K.; Miyanishi, M.; Russell, P.
A smooth affine surface $X$ defined over the complex field $\C$ is an $\ML_0$ surface if the
Makar--Limanov invariant $\ML(X)$ is trivial. In this paper we study the topology and geometry of
$\ML_0$ surfaces. Of particular interest is the question: Is every curve $C$ in $X$ which is isomorphic
to
the affine line a fiber component of an $\A^1$-fibration
on $X$? We shall show that the answer is affirmative if the Picard number
$\rho(X)=0$, but negative in case $\rho(X) \ge 1$. We shall also study the ascent and descent of
the $\ML_0$ property under proper maps.
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| 140 | On the Geometry of $p$-Typical Covers in Characteristic $p$ Kedlaya, Kiran S.
For $p$ a prime, a $p$-typical cover of a connected scheme on which $p=0$ is a finite
\'etale cover whose monodromy group (i.e., the Galois group of its
normal closure) is a $p$-group.
The geometry of such covers exhibits some unexpectedly pleasant
behaviors; building on work of Katz, we demonstrate some of these.
These include a criterion for when a morphism induces an isomorphism of
the $p$\nobreakdash-typi\-cal quotients of the \'etale fundamental groups,
and a decomposition theorem for $p$-typical covers of polynomial rings
over an algebraically closed field.
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| 164 | Boundary Structure of Hyperbolic $3$-Manifolds Admitting Annular and Toroidal Fillings at Large Distance Lee, Sangyop; Teragaito, Masakazu
For a hyperbolic $3$-manifold $M$ with a torus boundary component,
all but finitely many Dehn fillings yield hyperbolic $3$-manifolds.
In this paper, we will focus on the situation where
$M$ has two exceptional Dehn fillings: an annular filling and a toroidal filling.
For such a situation, Gordon gave an upper bound of $5$ for the distance between such slopes.
Furthermore, the distance $4$ is realized only by two specific manifolds, and $5$
is realized by a single manifold.
These manifolds all have a union of two tori as their boundaries.
Also, there is a manifold with three tori as its boundary which realizes the distance $3$.
We show that if the distance is $3$ then the boundary of the manifold consists of at most three tori.
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| 189 | Furstenberg Transformations and Approximate Conjugacy Lin, Huaxin
Let $\alpha$ and
$\beta$ be two Furstenberg transformations on $2$-torus associated
with irrational numbers $\theta_1,$ $\theta_2,$ integers $d_1, d_2$ and Lipschitz functions
$f_1$ and $f_2$. It is shown that $\alpha$ and $\beta$ are approximately conjugate in a
measure theoretical sense if (and only
if) $\overline{\theta_1\pm \theta_2}=0$ in $\R/\Z.$ Closely related to the classification of simple
amenable \CAs, it is shown that $\af$ and $\bt$ are approximately $K$-conjugate if (and only if)
$\overline{\theta_1\pm \theta_2}=0$ in $\R/\Z$ and $|d_1|=|d_2|.$ This
is also shown to be equivalent to the condition that the associated crossed product \CAs are isomorphic.
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| 208 | Constructing Galois Representations with Very Large Image Ramakrishna, Ravi
Starting with a 2-dimensional mod $p$ Galois representation, we
construct a deformation to a power series ring in infinitely many
variables over the $p$-adics. The image of this representation is full
in the sense that it contains $\SL_2$ of this power series
ring. Furthermore, all ${\mathbb Z}_p$ specializations of this
deformation are potentially semistable at $p$.
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| 222 | Amibes de sommes d'exponentielles Silipo, James
L'objectif de cet article est d'\'etudier la notion d'amibe au sens de
Favorov pour les syst\`emes finis de sommes d'exponentielles \`a
fr\'equences r\'eelles et de montrer que, sous des hypoth\`eses de
g\'en\'ericit\'e sur les fr\'equences, le compl\'ementaire de l'amibe
d'un syst\`eme de~$(k+1)$ sommes d'exponentielles \`a fr\'equences
r\'eelles est un sous-ensemble $k$-convexe au sens d'Henriques.
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| 241 | Semi-Classical Wavefront Set and Fourier Integral Operators Alexandrova, Ivana
Here we define and prove some properties of the semi-classical
wavefront set. We also define and study semi-classical Fourier
integral operators and prove a generalization of Egorov's theorem to
manifolds of different dimensions.
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| 264 | Erratum to: An Exactly Solved Model for Recombination, Mutation and Selection Baake, Michael; Baake, Ellen
.
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| 266 | Invariants and Coinvariants of the Symmetric Group in Noncommuting Variables Bergeron, Nantel; Reutenauer, Christophe; Rosas, Mercedes; Zabrocki, Mike
We introduce a natural Hopf algebra structure on the space of noncommutative
symmetric functions.
The bases for this algebra are indexed
by set partitions. We show that there exists a natural inclusion of the Hopf
algebra of noncommutative symmetric functions
in this larger space. We also consider this algebra as a subspace of
noncommutative polynomials and use it to
understand the structure of the spaces of harmonics and coinvariants
with respect to this collection of noncommutative polynomials and conclude
two analogues of Chevalley's theorem in the noncommutative setting.
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| 297 | Transitive Factorizations in the Hyperoctahedral Group Bini, G.; Goulden, I. P.; Jackson, D. M.
The classical Hurwitz enumeration problem has a presentation in terms of
transitive factorizations in the symmetric group. This presentation suggests
a generalization from type~$A$ to other
finite reflection groups and, in particular, to type~$B$.
We study this generalization both from a combinatorial and a geometric
point of view, with the prospect of providing a means of understanding more
of the structure of the moduli spaces of maps with an $\gS_2$-symmetry.
The type~$A$ case has been well studied and connects Hurwitz numbers
to the moduli space of curves. We conjecture an analogous setting for the
type~$B$ case that is studied here.
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| 313 | Asymptotic Properties for Increments of $l^{\infty}$-Valued Gaussian Random Fields Choi, Yong-Kab; o, Miklós Csörg\H
This paper establishes general theorems which contain both moduli
of continuity and large incremental results for $l^\infty$-valued Gaussian
random fields indexed by a multidimensional parameter under explicit conditions.
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| 334 | Low-Pass Filters and Scaling Functions for Multivariable Wavelets Curry, Eva
We show that a characterization of scaling functions for
multiresolution analyses given by Hern\'{a}ndez and Weiss and that a
characterization of low-pass filters given by Gundy both hold for
multivariable multiresolution analyses.
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| 348 | Monoidal Functors, Acyclic Models and Chain Operads Santos, F. Guillén; Navarro, V.; Pascual, P.; Roig, Agust{\'\i}
We prove that for a topological operad $P$ the operad of oriented
cubical singular chains, $C^{\ord}_\ast(P)$, and the operad of
simplicial singular chains, $S_\ast(P)$, are weakly equivalent. As
a consequence, $C^{\ord}_\ast(P\nsemi\mathbb{Q})$ is formal if and only
if $S_\ast(P\nsemi\mathbb{Q})$ is formal, thus linking together some
formality results which are spread out in the literature. The proof
is based on an acyclic models theorem for monoidal functors. We
give different variants of the acyclic models theorem and apply
the contravariant case to study the cohomology theories for
simplicial sets defined by $R$-simplicial differential graded
algebras.
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| 379 | Finite Cohen--Macaulay Type and Smooth Non-Commutative Schemes rgensen, Peter J\o
A commutative local Cohen--Macaulay ring $R$ of finite Cohen--Macaulay type is known to be an isolated
singularity; that is, $\Spec(R) \setminus \{ \mathfrak {m} \}$ is smooth.
This paper proves a non-commutative analogue. Namely, if $A$ is a
(non-commutative) graded Artin--Schelter \CM\ algebra which is fully
bounded Noetherian and
has finite Cohen--Macaulay type, then the non-commutative projective scheme determined by
$A$ is smooth.
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| 391 | The Geometry of the Weak Lefschetz Property and Level Sets of Points Migliore, Juan C.
In a recent paper, F. Zanello showed that level Artinian algebras in 3
variables can fail to have the Weak Lefschetz Property (WLP), and can
even fail to have unimodal Hilbert function. We show that the same is
true for the Artinian reduction of reduced, level sets of points in
projective 3-space. Our main goal is to begin an understanding of how
the geometry of a set of points can prevent its Artinian reduction
from having WLP, which in itself is a very algebraic notion. More
precisely, we produce level sets of points whose Artinian reductions
have socle types 3 and 4 and arbitrary socle degree $\geq 12$ (in the
worst case), but fail to have WLP. We also produce a level set of
points whose Artinian reduction fails to have unimodal Hilbert
function; our example is based on Zanello's example. Finally, we show
that a level set of points can have Artinian reduction that has WLP
but fails to have the Strong Lefschetz Property. While our
constructions are all based on basic double G-linkage, the
implementations use very different methods.
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| 412 | Quelques calculs de traces compactes et leurs transform{ées de Satake Nguyen-Chu, G.-V.
On calcule les restrictions {\`a} l'alg{\`e}bre de Hecke sph{\'e}rique
des traces tordues compactes d'un ensemble de repr{\'e}sentations
explicitement construites du groupe $\GL(N, F)$, o{\`u} $F$ est
un corps $p$-adique. Ces calculs r\'esolve en particulier une
question pos{\'e}e dans un article pr\'ec\'edent du m\^eme auteur.
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| 443 | On a Class of Projectively Flat Metrics with Constant Flag Curvature Shen, Z.; Yildirim, G. Civi
In this paper, we find equations that characterize locally
projectively flat Finsler metrics in the form $F = (\alpha +
\beta)^2/\alpha$, where $\alpha=\sqrt{a_{ij}y^iy^j}$ is a Riemannian
metric and $\beta= b_i y^i$ is a $1$-form. Then we completely
determine the local structure of those with constant flag curvature.
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| 457 | Harmonic Coordinates on Fractals with Finitely Ramified Cell Structure Teplyaev, Alexander
We define sets with finitely ramified cell structure, which are
generalizations of post-crit8cally finite self-similar
sets introduced by Kigami and of fractafolds introduced by Strichartz. In general,
we do not assume even local self-similarity, and allow countably many cells
connected at each junction point.
In particular, we consider post-critically infinite fractals.
We prove that if Kigami's resistance form
satisfies certain assumptions, then there exists a weak Riemannian metric
such that the energy can be expressed as the integral of the norm squared
of a weak gradient with respect to an energy measure.
Furthermore, we prove that if such a set can be homeomorphically represented
in harmonic coordinates, then for smooth functions the weak gradient can be
replaced by the usual gradient.
We also prove a simple formula for the energy measure Laplacian in harmonic
coordinates.
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| 481 | Heegner Points and the Rank of Elliptic Curves over Large Extensions of Global Fields Breuer, Florian; Im, Bo-Hae
Let $k$ be a global field, $\overline{k}$ a separable
closure of $k$, and $G_k$ the absolute Galois group
$\Gal(\overline{k}/k)$ of $\overline{k}$ over $k$. For every
$\sigma\in G_k$, let $\ks$ be the fixed subfield of $\overline{k}$
under $\sigma$. Let $E/k$ be an elliptic curve over $k$. It is known
that the Mordell--Weil group $E(\ks)$ has infinite rank. We present a
new proof of this fact in the following two cases. First, when $k$
is a global function field of odd characteristic and $E$ is
parametrized by a Drinfeld modular curve, and secondly when $k$ is a
totally real number field and $E/k$ is parametrized by a Shimura
curve. In both cases our approach uses the non-triviality of a
sequence of Heegner points on $E$ defined over ring class fields.
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| 491 | A Multi-Frey Approach to Some Multi-Parameter Families of Diophantine Equations Bugeaud, Yann; Mignotte, Maurice; Siksek, Samir
We solve several multi-parameter families of binomial Thue equations of arbitrary
degree; for example, we solve the equation
\[
5^u x^n-2^r 3^s y^n= \pm 1,
\]
in non-zero integers $x$, $y$ and positive integers $u$, $r$, $s$ and $n \geq 3$.
Our approach uses several Frey curves simultaneously, Galois representations
and level-lowering, new lower bounds for linear
forms in $3$ logarithms due to Mignotte and a famous theorem of Bennett on binomial
Thue equations.
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| 520 | Matrices Whose Norms Are Determined by Their Actions on Decreasing Sequences Chen, Chang-Pao; Huang, Hao-Wei; Shen, Chun-Yen
Let $A=(a_{j,k})_{j,k \ge 1}$ be a non-negative matrix. In this
paper, we characterize those $A$ for which $\|A\|_{E, F}$ are
determined by their actions on decreasing sequences, where $E$ and
$F$ are suitable normed Riesz spaces of sequences. In particular,
our results can apply to the following spaces: $\ell_p$, $d(w,p)$,
and $\ell_p(w)$. The results established here generalize
ones given by Bennett; Chen, Luor, and Ou; Jameson; and
Jameson and Lashkaripour.
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| 532 | Local Bounds for Torsion Points on Abelian Varieties Clark, Pete L.; Xarles, Xavier
We say that an abelian variety over a $p$-adic field $K$ has
anisotropic reduction (AR) if the special fiber of its N\'eron minimal
model does not contain a nontrivial split torus. This includes all
abelian varieties with potentially good reduction and, in particular,
those with complex or quaternionic multiplication. We give a bound for
the size of the $K$-rational torsion subgroup of a $g$-dimensional AR
variety depending only on $g$ and the numerical invariants of $K$ (the
absolute ramification index and the cardinality of the residue
field). Applying these bounds to abelian varieties over a number field
with everywhere locally anisotropic reduction, we get bounds which, as
a function of $g$, are close to optimal. In particular, we determine
the possible cardinalities of the torsion subgroup of an AR abelian
surface over the rational numbers, up to a set of 11 values which are
not known to occur. The largest such value is 72.
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| 556 | Polarization of Separating Invariants Draisma, Jan; Kemper, Gregor; Wehlau, David
We prove a characteristic free version of Weyl's theorem on
polarization. Our result is an exact analogue of Weyl's theorem, the
difference being that our statement is about separating invariants
rather than generating invariants. For the special case of finite
group actions we introduce the concept of cheap polarization,
and show that it is enough to take cheap polarizations of invariants
of just one copy of a representation to obtain separating vector
invariants for any number of copies. This leads to upper bounds on
the number and degrees of separating vector invariants of finite
groups.
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| 572 | Non-Selfadjoint Perturbations of Selfadjoint Operators in Two Dimensions IIIa. One Branching Point Hitrik, Michael; Sj{östrand, Johannes
This is the third in a series of works devoted to spectral
asymptotics for non-selfadjoint
perturbations of selfadjoint $h$-pseudodifferential operators in dimension 2, having a
periodic classical flow. Assuming that the strength $\epsilon$
of the perturbation is in the range $h^2\ll \epsilon \ll h^{1/2}$
(and may sometimes reach even smaller values), we
get an asymptotic description of the eigenvalues in rectangles
$[-1/C,1/C]+i\epsilon [F_0-1/C,F_0+1/C]$, $C\gg 1$, when $\epsilon F_0$ is a saddle point
value of the flow average of the leading perturbation.
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| 658 | Inverse Pressure Estimates and the Independence of Stable Dimension for Non-Invertible Maps Mihailescu, Eugen; Urba\'nski, Mariusz
We study the case of an Axiom A holomorphic non-degenerate
(hence non-invertible) map $f\from\mathbb P^2
\mathbb C \to \mathbb P^2 \mathbb C$, where $\mathbb P^2 \mathbb C$
stands for the complex
projective space of dimension 2. Let $\Lambda$ denote a basic set for
$f$ of unstable index 1, and $x$ an arbitrary point of $\Lambda$; we
denote by $\delta^s(x)$ the Hausdorff dimension of $W^s_r(x) \cap
\Lambda$, where $r$ is some fixed positive number and $W^s_r(x)$ is
the local stable manifold at $x$ of size $r$; $\delta^s(x)$ is called
the stable dimension at $x$. Mihailescu and
Urba\'nski introduced a notion of inverse topological pressure,
denoted by $P^-$, which takes into consideration preimages of points.
Manning and McCluskey study the case of hyperbolic diffeomorphisms on
real surfaces and give formulas for Hausdorff dimension. Our
non-invertible situation is different here since the local unstable
manifolds are not uniquely determined by their base point, instead
they depend in general on whole prehistories of the base points. Hence
our methods are different and are based on using a sequence of inverse
pressures for the iterates of $f$, in order to give upper and lower
estimates of the stable dimension. We obtain an estimate of the
oscillation of the stable dimension on $\Lambda$. When each point $x$
from $\Lambda$ has the same number $d'$ of preimages in $\Lambda$,
then we show that $\delta^s(x)$ is independent
of $x$; in fact $\delta^s(x)$ is shown to be equal in this case with
the unique zero of the map $t \to P(t\phi^s - \log d')$. We also
prove the Lipschitz continuity of the stable vector spaces over
$\Lambda$; this proof is again different than the one for
diffeomorphisms (however, the unstable distribution is not always
Lipschitz for conformal non-invertible maps). In the end we include
the corresponding results for a real conformal setting.
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| 685 | Closed and Exact Functions in the Context of Ginzburg--Landau Models Savu, Anamaria
For a general vector field we exhibit two Hilbert spaces, namely
the space of so called closed functions and the space of exact functions
and we calculate the codimension of the space of exact functions
inside the larger space of closed functions.
In particular we provide a new approach for the known cases:
the Glauber field and the second-order Ginzburg--Landau field
and for the case of the fourth-order Ginzburg--Landau field.
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| 703 | $\mathcal{Z}$-Stable ASH Algebras Toms, Andrew S.; Winter, Wilhelm
The Jiang--Su algebra $\mathcal{Z}$ has come to prominence in the
classification program for nuclear $C^*$-algebras of late, due
primarily to the fact that Elliott's classification conjecture in its
strongest form predicts that all simple, separable, and nuclear
$C^*$-algebras with unperforated $\mathrm{K}$-theory will absorb
$\mathcal{Z}$ tensorially, i.e., will be $\mathcal{Z}$-stable. There
exist counterexamples which suggest that the conjecture will only hold
for simple, nuclear, separable and $\mathcal{Z}$-stable
$C^*$-algebras. We prove that virtually all classes of nuclear
$C^*$-algebras for which the Elliott conjecture has been confirmed so
far consist of $\mathcal{Z}$-stable $C^*$-algebras. This
follows in large part from the following result, also proved herein:
separable and approximately divisible $C^*$-algebras are
$\mathcal{Z}$-stable.
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| 721 | Uniform Linear Bound in Chevalley's Lemma Adamus, J.; Bierstone, E.; Milman, P. D.
We obtain a uniform linear bound for the Chevalley function at a point in
the source of an analytic mapping that is regular in the sense of
Gabrielov. There is a version of
Chevalley's lemma also along a fibre, or at a point of the image of a proper
analytic mapping. We get a uniform linear bound for the Chevalley
function of a closed Nash (or formally Nash) subanalytic set.
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| 734 | Genus 2 Curves with Quaternionic Multiplication Baba, Srinath; Granath, H\aa kan
We explicitly construct the canonical rational models of Shimura
curves, both analytically in terms of modular forms and
algebraically in terms of coefficients of genus 2 curves, in the
cases of quaternion algebras of discriminant 6 and 10. This emulates
the classical construction in the elliptic curve case. We also give
families of genus 2 QM curves, whose Jacobians are the corresponding
abelian surfaces on the Shimura curve, and with coefficients that
are modular forms of weight 12. We apply these results to show
that our $j$-functions are supported exactly at those primes where
the genus 2 curve does not admit potentially good reduction, and
construct fields where this potentially good reduction is attained.
Finally, using $j$, we construct the fields of moduli and definition
for some moduli problems associated to the Atkin--Lehner group
actions.
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| 758 | On the Hyperinvariant Subspace Problem. IV Bercovici, H.; Foias, C.; Pearcy, C.
This paper is a continuation of three recent articles
concerning the structure of hyperinvariant
subspace lattices of operators on a (separable, infinite dimensional)
Hilbert space $\mathcal{H}$. We show herein, in particular, that
there exists a ``universal'' fixed block-diagonal operator $B$ on
$\mathcal{H}$ such that if $\varepsilon>0$ is given and $T$ is
an arbitrary nonalgebraic operator on $\mathcal{H}$, then there exists
a compact operator $K$ of norm less than $\varepsilon$ such that
(i) $\Hlat(T)$ is isomorphic as a complete lattice to $\Hlat(B+K)$
and (ii) $B+K$ is a quasidiagonal, $C_{00}$, (BCP)-operator with
spectrum and left essential spectrum the unit disc. In the last four
sections of the paper, we investigate the possible structures of the
hyperlattice of an arbitrary algebraic operator. Contrary to existing
conjectures, $\Hlat(T)$ need not be generated by the ranges and kernels
of the powers of $T$ in the nilpotent case. In fact, this lattice
can be infinite.
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| 790 | Types, paquets et changement de base : l'exemple de $U(2,1)(F_0)$. I. Types simples maximaux et paquets singletons Blasco, Laure
Soit $F_0$ un corps local non archim\'edien de caract\'eristique
nulle et de ca\-rac\-t\'eristique r\'esiduelle impaire.
J. Rogawski a montr\'e l'existence du changement de base entre le
groupe unitaire en trois variables $U(2,1)(F_{0})$, d\'efini
relativement \`a une extension quadratique $F$ de $F_{0}$, et le
groupe lin\'eaire $GL(3,F)$. Par ailleurs, nous
avons d\'ecrit les repr\'esentations supercuspidales irr\'eductibles
de $U(2,1)(F_{0})$ comme induites \`a partir d'un sous-groupe compact
ouvert de $U(2,1)(F_{0})$, description analogue \`a celle des
repr\'esentations admissibles irr\'eductibles de $GL(3,F)$ obtenue
par C. Bushnell et P. Kutzko. A partir de ces
descriptions, nous construisons explicitement le changement de base
des repr\'esentations tr\`es cuspidales de $U(2,1)(F_{0})$.
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| 822 | Maximum Principles for Subharmonic Functions Via Local Semi-Dirichlet Forms Kuwae, Kazuhiro
Maximum principles for subharmonic
functions in the framework of quasi-regular local semi-Dirichlet
forms admitting lower bounds are presented.
As applications, we give
weak and strong maximum principles
for (local) subsolutions of a second order elliptic
differential operator on the domain of Euclidean space under conditions on coefficients,
which partially generalize the results by Stampacchia.
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| 875 | A Characterization of the Quantum Cohomology Ring of $G/B$ and Applications Mare, Augustin-Liviu
We observe that the small quantum product of the
generalized flag manifold $G/B$ is a product operation $\star$ on
$H^*(G/B)\otimes \bR[q_1,\dots, q_l]$ uniquely determined by the
facts
that: it is a deformation of the cup product on $H^*(G/B)$; it is
commutative, associative, and graded with respect to $\deg(q_i)=4$; it
satisfies a certain relation (of degree two); and the corresponding
Dubrovin connection is flat. Previously, we proved that these
properties alone imply the presentation of the ring $(H^*(G/B)\otimes
\bR[q_1,\dots, q_l],\star)$ in terms of generators and relations. In
this paper we use the above observations to give conceptually new
proofs of other fundamental results of the quantum Schubert calculus
for $G/B$: the quantum Chevalley formula of D. Peterson (see also
Fulton and Woodward ) and the ``quantization by standard
monomials" formula of Fomin, Gelfand, and Postnikov for
$G=\SL(n,\bC)$. The main idea of the proofs is the same as in
Amarzaya--Guest: from the quantum $\D$-module of $G/B$ one can
decode all information about the quantum cohomology of this space.
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| 892 | The Second Cohomology of Current Algebras of General Lie Algebras Neeb, Karl-Hermann; Wagemann, Friedrich
Let $A$ be a unital commutative associative algebra over a field of
characteristic zero, $\k$ a Lie algebra, and
$\zf$ a vector space, considered as a trivial module of the Lie algebra
$\gf := A \otimes \kf$. In this paper, we give a
description of the cohomology space $H^2(\gf,\zf)$
in terms of easily accessible data associated with $A$ and $\kf$.
We also discuss the topological situation, where
$A$ and $\kf$ are locally convex algebras.
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| 923 | Endomorphisms of Kronecker Modules Regulated by Quadratic Algebra Extensions of a Function Field Okoh, F.; Zorzitto, F.
The Kronecker modules $\mathbb{V}(m,h,\alpha)$, where $m$ is a positive integer, $h$ is
a height function, and $\alpha$ is a $K$-linear functional on the
space $K(X)$ of rational functions in one variable $X$ over an
algebraically closed field $K$, are models for the family of all
torsion-free rank-2 modules that are extensions of finite-dimensional
rank-1 modules. Every such module comes with a regulating polynomial
$f$ in $K(X)[Y]$. When the endomorphism algebra of $\mathbb{V}(m,h,\alpha)$ is
commutative and non-trivial, the regulator $f$ must be quadratic in
$Y$. If $f$ has one repeated root in $K(X)$, the endomorphism algebra
is the trivial extension $K\ltimes S$ for some vector space $S$. If
$f$ has distinct roots in $K(X)$, then the endomorphisms form a
structure that we call a bridge. These include the coordinate rings
of some curves. Regardless of the number of roots in the regulator,
those $\End\mathbb{V}(m,h,\alpha)$ that are domains have zero radical. In addition,
each semi-local $\End\mathbb{V}(m,h,\alpha)$ must be either a trivial extension
$K\ltimes S$ or the product $K\times K$.
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| 958 | A Note on a Conjecture of S. Stahl Chen, Yichao
S. Stahl (Canad. J. Math. \textbf{49}(1997), no. 3, 617--640)
conjectured that the zeros of genus polynomial are real.
L. Liu and Y. Wang disproved this conjecture on the basis
of Example 6.7. In this note, it is pointed out
that there is an error in this example and a new generating matrix
and initial vector are provided.
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| 960 | Erratum: On the Zeros of Some Genus Polynomials Stahl, Saul
No abstract.
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| 961 | About the Defectivity of Certain Segre--Veronese Varieties Abrescia, Silvia
We study the regularity of the higher secant varieties of $\PP^1\times
\PP^n$, embedded with divisors of type $(d,2)$ and $(d,3)$. We
produce, for the highest defective cases, a ``determinantal'' equation
of the secant variety. As a corollary, we prove that the Veronese
triple embedding of $\PP^n$ is not Grassmann defective.
|
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| 975 | An AF Algebra Associated with the Farey Tessellation Boca, Florin P.
We associate with the Farey tessellation of the upper
half-plane an
AF algebra $\AA$ encoding the ``cutting sequences'' that define
vertical geodesics.
The Effros--Shen AF algebras arise as quotients
of $\AA$. Using the path algebra model for AF algebras we construct, for
each $\tau \in \big(0,\frac{1}{4}\big]$, projections $(E_n)$ in
$\AA$ such that $E_n E_{n\pm 1}E_n \leq \tau E_n$.
|
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| 1001 | Isometric Group Actions on Hilbert Spaces: Structure of Orbits Cornulier, Yves de; Tessera, Romain; Valette, Alain
Our main result is that a finitely generated nilpotent group has
no isometric action on an infinite-dimensional Hilbert space with
dense orbits. In contrast, we construct such an action with a
finitely generated metabelian group.
|
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| 1010 | $H^\infty$ Functional Calculus and Mikhlin-Type Multiplier Conditions Galé, José E.; Miana, Pedro J.
Let $T$ be a sectorial operator. It is known that the existence of a
bounded (suitably scaled) $H^\infty$ calculus for $T$, on every
sector containing the positive half-line, is equivalent to the
existence of a bounded functional calculus on the Besov algebra
$\Lambda_{\infty,1}^\alpha(\R^+)$. Such an algebra
includes functions defined by Mikhlin-type conditions and so the
Besov calculus can be seen as a result on multipliers for $T$. In
this paper, we use fractional derivation to analyse in detail the
relationship between $\Lambda_{\infty,1}^\alpha$ and Banach algebras
of Mikhlin-type. As a result, we obtain a new version of the quoted
equivalence.
|
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| 1028 | Lifting $n$-Dimensional Galois Representations Hamblen, Spencer
We investigate the problem of deforming $n$-dimensional mod $p$ Galois
representations to characteristic zero. The existence of 2-dimensional
deformations has been proven under certain conditions
by allowing ramification at additional primes in order to
annihilate a dual Selmer group. We use the same general methods to
prove the existence of $n$-dimensional deformations.
|
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| 1050 | Adjacency Preserving Maps on Hermitian Matrices Huang, Wen-ling; Semrl, Peter \v
Hua's fundamental theorem of the geometry of hermitian matrices
characterizes bijective maps on the space of all $n\times n$
hermitian matrices preserving adjacency in both directions.
The problem of possible improvements
has been open for a while. There are three natural problems here.
Do we need the bijectivity assumption? Can we replace the
assumption of preserving adjacency in both directions by the
weaker assumption of preserving adjacency in one direction only?
Can we obtain such a characterization for maps acting between the
spaces of hermitian matrices of different sizes? We answer all
three questions for the complex hermitian matrices, thus obtaining
the optimal structural result for adjacency preserving maps on
hermitian matrices over the complex field.
|
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| 1067 | On Types for Unramified $p$-Adic Unitary Groups Kariyama, Kazutoshi
Let $F$ be a non-archimedean local field of residue characteristic
neither 2 nor 3 equipped with a galois involution with fixed field
$F_0$, and let $G$ be a symplectic group over $F$ or an unramified
unitary group over $F_0$. Following the methods of Bushnell--Kutzko for
$\GL(N,F)$, we define an analogue of a simple type attached to a
certain skew simple stratum, and realize a type in $G$. In
particular, we obtain an irreducible supercuspidal representation of
$G$ like $\GL(N,F)$.
|
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| 1108 | A Classification of Tsirelson Type Spaces Lopez-Abad, J.; Manoussakis, A.
We give a complete classification of mixed Tsirelson spaces
$T[(\mathcal F_i,\theta_i)_{i=1}^{r}]$ for finitely many pairs of
given compact and hereditary families $\mathcal F_i$ of finite sets of
integers and $0<\theta_i<1$ in terms of the Cantor--Bendixson indices
of the families $\mathcal F_i$, and $\theta_i$ ($1\le i\le r$). We
prove that there are unique countable ordinal $\alpha$ and
$0<\theta<1$ such that every block sequence of
$T[(\mathcal F_i,\theta_i)_{i=1}^{r}]$ has a subsequence equivalent to a
subsequence of the natural basis of the
$T(\mathcal S_{\omega^\alpha},\theta)$. Finally, we give a complete criterion of
comparison in between two of these mixed Tsirelson spaces.
|
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| 1149 | Conjugate Reciprocal Polynomials with All Roots on the Unit Circle Petersen, Kathleen L.; Sinclair, Christopher D.
We study the geometry, topology and Lebesgue measure of the set of
monic conjugate reciprocal polynomials of fixed degree with all
roots on the unit circle. The set of such polynomials of degree $N$
is naturally associated to a subset of $\R^{N-1}$. We calculate
the volume of this set, prove the set is homeomorphic to the $N-1$
ball and that its isometry group is isomorphic to the dihedral
group of order $2N$.
|
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| 1168 | Short Time Behavior of Solutions to Linear and Nonlinear Schr{ödinger Equations Taylor, Michael
We examine the fine structure of the short time behavior
of solutions to various linear and nonlinear Schr{\"o}dinger equations
$u_t=i\Delta u+q(u)$ on $I\times\RR^n$, with initial data $u(0,x)=f(x)$.
Particular attention is paid to cases where $f$ is piecewise smooth,
with jump across an $(n-1)$-dimensional surface. We give detailed
analyses of Gibbs-like phenomena and also focusing effects, including
analogues of the Pinsky phenomenon. We give results for general $n$
in the linear case. We also have detailed analyses for a broad class of
nonlinear equations when $n=1$ and $2$, with emphasis on the analysis of
the first order correction to the solution of the corresponding linear
equation. This work complements estimates on the error in this approximation.
|
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| 1201 | Hölder Compactification for Some Manifolds with Pinched Negative Curvature Near Infinity Bahuaud, Eric; Marsh, Tracey
We consider a complete noncompact Riemannian manifold $M$ and give
conditions on a compact submanifold $K \subset M$ so that the outward
normal exponential map off the boundary of $K$ is a diffeomorphism
onto $\MlK$. We use this to compactify $M$ and show that pinched
negative sectional curvature outside $K$ implies $M$ has a
compactification with a well-defined H\"older structure independent of
$K$. The H\"older constant depends on the ratio of the curvature
pinching. This extends and generalizes a 1985 result of Anderson and
Schoen.
|
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| 1219 | CR Extension from Manifolds of Higher Type Baracco, Luca; Zampieri, Giuseppe
This paper deals with the extension of CR functions
from a manifold $M\subset \mathbb C^n$ into directions produced by higher
order commutators of holomorphic and antiholomorphic vector fields. It
uses the theory of complex ``sectors'' attached to real submanifolds
introduced in recent joint work of the authors with D. Zaitsev. In
addition, it develops a new technique of approximation of sectors by
smooth discs.
|
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| 1240 | Categorification of the Colored Jones Polynomial and Rasmussen Invariant of Links Beliakova, Anna; Wehrli, Stephan
We define a family of formal Khovanov brackets
of a colored link depending on two parameters.
The isomorphism classes of these brackets are
invariants of framed colored links.
The Bar-Natan functors applied to these brackets
produce Khovanov and Lee homology theories categorifying the colored
Jones polynomial. Further,
we study conditions under which
framed colored link cobordisms induce chain transformations between
our formal brackets. We conjecture that
for special choice of parameters, Khovanov and Lee homology theories
of colored links are functorial (up to sign).
Finally, we extend the Rasmussen invariant to links and give examples
where this invariant is a stronger obstruction to sliceness
than the multivariable Levine--Tristram signature.
|
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| 1267 | Nonadjacent Radix-$\tau$ Expansions of Integers in Euclidean Imaginary Quadratic Number Fields Blake, Ian F.; Murty, V. Kumar; Xu, Guangwu
In his seminal papers, Koblitz proposed curves
for cryptographic use. For fast operations on these curves,
these papers also
initiated a study of the radix-$\tau$ expansion of integers in the number
fields $\Q(\sqrt{-3})$ and $\Q(\sqrt{-7})$. The (window)
nonadjacent form of $\tau$-expansion of integers in
$\Q(\sqrt{-7})$ was first investigated by Solinas.
For integers in $\Q(\sqrt{-3})$, the nonadjacent form
and the window nonadjacent form of the $\tau$-expansion were
studied. These are used for efficient
point multiplications on Koblitz curves.
In this paper, we complete
the picture by producing the (window)
nonadjacent radix-$\tau$ expansions
for integers in all Euclidean imaginary quadratic number fields.
|
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| 1283 | Remarks on Littlewood--Paley Analysis Ho, Kwok-Pun
Littlewood--Paley analysis is generalized in
this article. We show that the compactness of the Fourier support
imposed on the analyzing function can be removed. We also prove
that the Littlewood--Paley decomposition of tempered distributions
converges under a topology stronger than the weak-star topology,
namely, the inductive limit topology. Finally, we construct a
multiparameter Littlewood--Paley analysis and obtain the
corresponding ``renormalization'' for the convergence of this
multiparameter Littlewood--Paley analysis.
|
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| 1306 | Theta Lifts of Tempered Representations for Dual Pairs $(\Sp_{2n}, O(V))$ Mui\'c, Goran
This paper is the continuation of our previous work on the explicit
determination of the structure of theta lifts for dual pairs
$(\Sp_{2n}, O(V))$ over a non-archimedean field $F$ of characteristic
different than $2$, where $n$ is the split rank of $\Sp_{2n}$ and the
dimension of the space $V$ (over $F$) is even. We determine the
structure of theta lifts of tempered representations in terms of theta
lifts of representations in discrete series.
|
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| 1336 | Moving Frames for Lie Pseudo--Groups Olver, Peter J.; Pohjanpelto, Juha
We propose a new, constructive theory of moving frames for Lie
pseudo-group actions on submanifolds. The moving frame provides an
effective means for determining complete systems of differential
invariants and invariant differential forms, classifying their
syzygies and recurrence relations, and solving equivalence and
symmetry problems arising in a broad range of applications.
|
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| 1387 | On $n$-Dimensional Steinberg Symbols Romo, Fernando Pablos
The aim of this work is to provide a new approach for constructing
$n$-dimensional Steinberg symbols on discrete valuation fields from
$(n+1)$-cocycles and to study reciprocity laws on curves related to
these symbols.
|
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| 1406 | Hauteur asymptotique des points de Heegner Ricotta, Guillaume; Vidick, Thomas
Geometric intuition suggests that the N\'{e}ron--Tate height of Heegner
points on a rational elliptic curve $E$ should be asymptotically
governed by the degree of its modular parametrisation. In this paper,
we show that this geometric intuition asymptotically holds on average
over a subset of discriminants. We also study the asymptotic behaviour
of traces of Heegner points on average over a subset of discriminants
and find a difference according to the rank of the elliptic curve. By
the Gross--Zagier formulae, such heights are related to the special
value at the critical point for either the derivative of the
Rankin--Selberg convolution of $E$ with a certain weight one theta
series attached to the principal ideal class of an imaginary quadratic
field or the twisted $L$-function of $E$ by a quadratic Dirichlet
character. Asymptotic formulae for the first moments associated with
these $L$-series and $L$-functions are proved, and experimental results
are discussed. The appendix contains some conjectural applications of
our results to the problem of the discretisation of odd quadratic
twists of elliptic curves.
|
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| 1437 | Author Index - Index des auteurs CJM
No abstract.
|
© Canadian Mathematical Society, 2013
© Canadian Mathematical Society, 2013 : http://www.cms.math.ca/