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arxiv_dataset-0704.0001
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Calculation of prompt diphoton production cross sections at Tevatron and
LHC energies
hep-ph
A fully differential calculation in perturbative quantum chromodynamics is
presented for the production of massive photon pairs at hadron colliders. All
next-to-leading order perturbative contributions from quark-antiquark,
gluon-(anti)quark, and gluon-gluon subprocesses are included, as well as
all-orders resummation of initial-state gluon radiation valid at
next-to-next-to-leading logarithmic accuracy. The region of phase space is
specified in which the calculation is most reliable. Good agreement is
demonstrated with data from the Fermilab Tevatron, and predictions are made for
more detailed tests with CDF and DO data. Predictions are shown for
distributions of diphoton pairs produced at the energy of the Large Hadron
Collider (LHC). Distributions of the diphoton pairs from the decay of a Higgs
boson are contrasted with those produced from QCD processes at the LHC, showing
that enhanced sensitivity to the signal can be obtained with judicious
selection of events.
|
arxiv topic:hep-ph
|
arxiv_dataset-1704.0101
|
The birth of string theory
hep-th
In this contribution we go through the developments that in the years 1968 to
1974 led from the Veneziano model to the bosonic string.
|
arxiv topic:hep-th
|
arxiv_dataset-2704.0201
|
Hecke-Clifford algebras and spin Hecke algebras I: the classical affine
type
math.RT math.QA
Associated to the classical Weyl groups, we introduce the notion of
degenerate spin affine Hecke algebras and affine Hecke-Clifford algebras. For
these algebras, we establish the PBW properties, formulate the intertwiners,
and describe the centers. We further develop connections of these algebras with
the usual degenerate (i.e. graded) affine Hecke algebras of Lusztig by
introducing a notion of degenerate covering affine Hecke algebras.
|
arxiv topic:math.RT math.QA
|
arxiv_dataset-3704.0301
|
Differential Recursion and Differentially Algebraic Functions
cs.CC
Moore introduced a class of real-valued "recursive" functions by analogy with
Kleene's formulation of the standard recursive functions. While his concise
definition inspired a new line of research on analog computation, it contains
some technical inaccuracies. Focusing on his "primitive recursive" functions,
we pin down what is problematic and discuss possible attempts to remove the
ambiguity regarding the behavior of the differential recursion operator on
partial functions. It turns out that in any case the purported relation to
differentially algebraic functions, and hence to Shannon's model of analog
computation, fails.
|
arxiv topic:cs.CC
|
arxiv_dataset-4704.0401
|
Modelling the Near-IR Spectra of Red Supergiant-dominated Populations
astro-ph
We report on recent progress in the modelling of the near-IR spectra of young
stellar populations, i.e. populations in which red supergiants (RSGs) are
dominant. First, we discuss the determination of fundamental parameters of RSGs
using fits to their near-IR spectra with new PHOENIX model spectra;
RSG-specific surface abundances are accounted for and effects of the
microturbulence parameter are explored. New population synthesis predictions
are then described and, as an example, it is shown that the spectra of young
star clusters in M82 can be reproduced very well from 0.5 to 2.4 micrometers.
We warn of remaining uncertainties in cluster ages.
|
arxiv topic:astro-ph
|
arxiv_dataset-5704.0501
|
On universality of critical behaviour in the focusing nonlinear
Schr\"odinger equation, elliptic umbilic catastrophe and the {\it
tritronqu\'ee} solution to the Painlev\'e-I equation
math.AP math-ph math.MP
We argue that the critical behaviour near the point of ``gradient
catastrophe" of the solution to the Cauchy problem for the focusing nonlinear
Schr\"odinger equation $ i\epsilon \psi_t +\frac{\epsilon^2}2\psi_{xx}+
|\psi|^2 \psi =0$ with analytic initial data of the form $\psi(x,0;\epsilon)
=A(x) e^{\frac{i}{\epsilon} S(x)}$ is approximately described by a particular
solution to the Painlev\'e-I equation.
|
arxiv topic:math.AP math-ph math.MP
|
arxiv_dataset-6704.0601
|
D-\bar D mixing and rare D decays in the Littlest Higgs model with
non-unitarity matrix
hep-ph hep-ex
We study the $D-\bar D$ mixing and rare D decays in the Littlest Higgs model.
As the new weak singlet quark with the electric charge of 2/3 is introduced to
cancel the quadratic divergence induced by the top-quark, the standard unitary
$3\times 3$ Cabibbo-Kobayashi-Maskawa matrix is extended to a non-unitary
$4\times 3$ matrix in the quark charged currents and Z-mediated flavor changing
neutral currents are generated at tree level. In this model, we show that the
$D-\bar D$ mixing parameter can be as large as the current experimental value
and the decay branching ratio (BR) of $D\to X_u \ga$ is small but its direct CP
asymmetry could be $O(10%)$. In addition, we find that the BRs of $D\to X_u
\ell^{+} \ell^{-}$, $D\to X_u\nu \bar \nu$ and $D\to \mu^{+} \mu^{-}$ could be
enhanced to be $O(10^{-9})$, $O(10^{-8})$ and $O(10^{-9})$, respectively.
|
arxiv topic:hep-ph hep-ex
|
arxiv_dataset-7704.0701
|
On thermal effects in solid state lasers: the case of ytterbium-doped
materials
physics.optics
A review of theoretical and experimental studies of thermal effects in
solid-state lasers is presented, with a special focus on diode-pumped
ytterbium-doped materials. A large part of this review provides however general
information applicable to any kind of solid-state laser. Our aim here is not to
make a list of the techniques that have been used to minimize thermal effects,
but instead to give an overview of the theoretical aspects underneath, and give
a state-of-the-art of the tools at the disposal of the laser scientist to
measure thermal effects. After a presentation of some general properties of
Yb-doped materials, we address the issue of evaluating the temperature map in
Yb-doped laser crystals, both theoretically and experimentally. This is the
first step before studying the complex problem of thermal lensing (part III).
We will focus on some newly discussed aspects, like the definition of the
thermo-optic coefficient: we will highlight some misleading interpretations of
thermal lensing experiments due to the use of the dn/dT parameter in a context
where it is not relevant. Part IV will be devoted to a state-of-the-art of
experimental techniques used to measure thermal lensing. Eventually, in part V,
we will give some concrete examples in Yb-doped materials, where their
peculiarities will be pointed out.
|
arxiv topic:physics.optics
|
arxiv_dataset-8704.0801
|
Fundamental solutions for a class of non-elliptic homogeneous
differential operators
math.AP math.GM
We compute temperate fundamental solutions of homogeneous differential
operators with real-principal type symbols. Via analytic continuation of
meromorphic distributions, fundamental solutions for these non-elliptic
operators can be constructed in terms of radial averages and invariant
distributions on the unit sphere.
|
arxiv topic:math.AP math.GM
|
arxiv_dataset-9704.0901
|
The density of critical percolation clusters touching the boundaries of
strips and squares
cond-mat.dis-nn cond-mat.stat-mech
We consider the density of two-dimensional critical percolation clusters,
constrained to touch one or both boundaries, in infinite strips, half-infinite
strips, and squares, as well as several related quantities for the infinite
strip. Our theoretical results follow from conformal field theory, and are
compared with high-precision numerical simulation. For example, we show that
the density of clusters touching both boundaries of an infinite strip of unit
width (i.e. crossing clusters) is proportional to $(\sin \pi
y)^{-5/48}\{[\cos(\pi y/2)]^{1/3} +[\sin (\pi y/2)]^{1/3}-1\}$.
We also determine numerically contours for the density of clusters crossing
squares and long rectangles with open boundaries on the sides, and compare with
theory for the density along an edge.
|
arxiv topic:cond-mat.dis-nn cond-mat.stat-mech
|
arxiv_dataset-10704.1001
|
Tautological relations in Hodge field theory
math.QA math.AG
We propose a Hodge field theory construction that captures algebraic
properties of the reduction of Zwiebach invariants to Gromov-Witten invariants.
It generalizes the Barannikov-Kontsevich construction to the case of higher
genera correlators with gravitational descendants.
We prove the main theorem stating that algebraically defined Hodge field
theory correlators satisfy all tautological relations. From this perspective
the statement that Barannikov-Kontsevich construction provides a solution of
the WDVV equation looks as the simplest particular case of our theorem. Also it
generalizes the particular cases of other low-genera tautological relations
proven in our earlier works; we replace the old technical proofs by a novel
conceptual proof.
|
arxiv topic:math.QA math.AG
|
arxiv_dataset-11704.1101
|
On the S_n-module structure of the noncommutative harmonics
math.CO math.RT
Using a noncommutative analog of Chevalley's decomposition of polynomials
into symmetric polynomials times coinvariants due to Bergeron, Reutenauer,
Rosas, and Zabrocki we compute the graded Frobenius series for their two sets
of noncommutative harmonics with respect to the left action of the symmetric
group (acting on variables). We use these results to derive the Frobenius
series for the enveloping algebra of the derived free Lie algebra in n
variables.
|
arxiv topic:math.CO math.RT
|
arxiv_dataset-12704.1201
|
Evaluation of the Axial Vector Commutator Sum Rule for Pion-Pion
Scattering
hep-ph
We consider the sum rule proposed by one of us (SLA), obtained by taking the
expectation value of an axial vector commutator in a state with one pion. The
sum rule relates the pion decay constant to integrals of pion-pion cross
sections, with one pion off the mass shell. We remark that recent data on
pion-pion scattering allow a precise evaluation of the sum rule. We also
discuss the related Adler--Weisberger sum rule (obtained by taking the
expectation value of the same commutator in a state with one nucleon),
especially in connection with the problem of extrapolation of the pion momentum
off its mass shell. We find, with current data, that both the pion-pion and
pion-nucleon sum rules are satisfied to better than six percent, and we give
detailed estimates of the experimental and extrapolation errors in the closure
discrepancies.
|
arxiv topic:hep-ph
|
arxiv_dataset-13704.1301
|
IRAS 18317-0757: A Cluster of Embedded Massive Stars and Protostars
astro-ph
We present high-resolution, multiwavelength continuum and molecular-line
images of the massive star forming region IRAS 18317-0757. The IR through mm
spectral energy distribution can be approximated by a two-temperature model (25
and 63 K) with a total luminosity of approximately log(L/Lsun)=5.2. Previous
submm imaging resolved this region into a cluster of 5 dust cores, one of which
is associated with the UCHII region G23.96+0.15, and another with an H2O maser.
In our new 2.7 mm continuum image, only the UCHII region is detected, with
total flux and morphology in good agreement with the free-free emission in VLA
cm-wave maps. For the other four objects, the nondetections at 2.7 mm and in
the MSX mid-IR bands are consistent with cool dust emission with a temperature
of 13-40K and luminosity of 1000-40000 Lsun. By combining single-dish and
interferometric data, we have identified over two dozen virialized C18O cores
in this region that contain ~40% of the total molecular gas mass present. While
the overall extent of the C18O and dust emission is similar, the emission peaks
do not correlate well in detail. At least 11 of the 123 stars identified by
2MASS in this region are likely to be within the star-forming cluster. Two
stars (both associated with the UCHII region) were previously identified as O
stars via IR spectroscopy. Most of the rest of the reddened stars have no
obvious correlation with the C18O cores or the dust cores. In summary, our
observations indicate that considerable fragmentation of the molecular cloud
has taken place during the time required for the UCHII region to form and the O
stars to become detectable at IR wavelengths. Additional star formation appears
to be ongoing on the periphery of the central region, where up to four B-type
(proto)stars have formed among a substantial number of C18O molecular cores.
|
arxiv topic:astro-ph
|
arxiv_dataset-14704.1401
|
Flat Pencils of Symplectic Connections and Hamiltonian Operators of
Degree 2
nlin.SI math.SG
Bi-Hamiltonian structures involving Hamiltonian operators of degree 2 are
studied. Firstly, pairs of degree 2 operators are considered in terms of an
algebra structure on the space of 1-forms, related to so-called Fermionic
Novikov algebras. Then, degree 2 operators are considered as deformations of
hydrodynamic type Poisson brackets.
|
arxiv topic:nlin.SI math.SG
|
arxiv_dataset-15704.1501
|
Surface Structure Analysis of Atomically Smooth BaBiO$_3$ Films
cond-mat.other
Using low energy Time-of-Flight Scattering and Recoil Spectroscopy (TOF-SARS)
and Mass Spectroscopy of Recoiled Ions (MSRI) we analyze the surface structure
of an atomically smooth BaBiO$_3$ film grown by molecular beam epitaxy. We
demonstrate high sensitivity of the TOF-SARS and MSRI spectra to slight changes
in the orientation of the ion scattering plane with respect to the
crystallographic axes. The observed angle dependence allows us to clearly
identify the termination layer as BiO$_2$. Our data also indicate that
angle-resolved MSRI data can be used for high resolution studies of surface
structure of complex oxide thin films.
|
arxiv topic:cond-mat.other
|
arxiv_dataset-16704.1601
|
Spontaneous symmetry breaking of solitons trapped in a double-channel
potential
nlin.PS
We consider a two-dimensional (2D) nonlinear Schrodinger equation with
self-focusing nonlinearity and a quasi-1D double-channel potential, i.e., a
straightforward 2D extension of the well-known double-well potential. The model
may be realized in terms of nonlinear optics and Bose-Einstein condensates. The
variational approximation (VA) predicts a bifurcation breaking the symmetry of
2D solitons trapped in the double channel, the bifurcation being of the
subcritical type. The predictions of the VA are confirmed by numerical
simulations. The work presents the first example of the spontaneous symmetry
breaking (SSB) of 2D solitons in any dual-core system.
|
arxiv topic:nlin.PS
|
arxiv_dataset-17704.1701
|
Noether's problem for some p-groups
math.AC math.RA
Let K be any field and G be a finite group. Noether's problem asks whether
the fixed field is rational (=purely transcendental) over K. We will prove that
if G is a non-abelian p-group of order p^n containing a cyclic subgroup of
index p and K is any field containing a primitive p^{n-2}-th root of unity,
then K(G) is rational over K.
|
arxiv topic:math.AC math.RA
|
arxiv_dataset-18704.1801
|
A calculation of the shear viscosity in SU(3) gluodynamics
hep-lat hep-ph
We perform a lattice Monte-Carlo calculation of the two-point functions of
the energy-momentum tensor at finite temperature in the SU(3) gauge theory.
Unprecedented precision is obtained thanks to a multi-level algorithm. The
lattice operators are renormalized non-perturbatively and the classical
discretization errors affecting the correlators are corrected for. A robust
upper bound for the shear viscosity to entropy density ratio is derived, eta/s
< 1.0, and our best estimate is eta/s = 0.134(33) at T=1.65Tc under the
assumption of smoothness of the spectral function in the low-frequency region.
|
arxiv topic:hep-lat hep-ph
|
arxiv_dataset-19704.1901
|
Classical Information Capacity of the Bosonic Broadcast Channel
quant-ph
We show that when coherent-state encoding is employed in conjunction with
coherent detection, the Bosonic broadcast channel is equivalent to a classical
degraded Gaussian broadcast channel whose capacity region is dual to that of
the classical Gaussian multiple-access channel. We further show that if a
minimum output-entropy conjecture holds true, then the ultimate classical
information capacity of the Bosonic broadcast channel can be achieved by a
coherent-state encoding. We provide some evidence in support of the conjecture.
|
arxiv topic:quant-ph
|
arxiv_dataset-20704.2001
|
Geometry of Parallelizable Manifolds in the Context of Generalized
Lagrange Spaces
gr-qc math.DG
In this paper, we deal with a generalization of the geometry of
parallelizable manifolds, or the absolute parallelism (AP-) geometry, in the
context of generalized Lagrange spaces. All geometric objects defined in this
geometry are not only functions of the positional argument $x$, but also depend
on the directional argument $y$. In other words, instead of dealing with
geometric objects defined on the manifold $M$, as in the case of classical
AP-geometry, we are dealing with geometric objects in the pullback bundle
$\pi^{-1}(TM)$ (the pullback of the tangent bundle $TM$ by $ \pi: T
M\longrightarrow M$). Many new geometric objects, which have no counterpart in
the classical AP-geometry, emerge in this more general context. We refer to
such a geometry as generalized AP-geometry (GAP-geometry). In analogy to
AP-geometry, we define a $d$-connection in $\pi^{-1}(TM)$ having remarkable
properties, which we call the canonical $d$-connection, in terms of the unique
torsion-free Riemannian $d$-connection. In addition to these two
$d$-connections, two more $d$-connections are defined, the dual and the
symmetric $d$-connections. Our space, therefore, admits twelve curvature
tensors (corresponding to the four defined $d$-connections), three of which
vanish identically. Simple formulae for the nine non-vanishing curvatures
tensors are obtained, in terms of the torsion tensors of the canonical
$d$-connection. The different $W$-tensors admitted by the space are also
calculated. All contractions of the $h$- and $v$-curvature tensors and the
$W$-tensors are derived. Second rank symmetric and skew-symmetric tensors,
which prove useful in physical applications, are singled out.
|
arxiv topic:gr-qc math.DG
|
arxiv_dataset-21704.2101
|
Momentum distribution and correlation of two-nucleon relative motion in
$^6$He and $^6$Li
nucl-th
The momentum distribution of relative motion between two nucleons gives
information on the correlation in nuclei. The momentum distribution is
calculated for both $^{6}$He and $^6$Li which are described in a three-body
model of $\alpha$+$N$+$N$. The ground state solution for the three-body
Hamiltonian is obtained accurately using correlated basis functions. The
momentum distribution depends on the potential model for the $N$-$N$
interaction. With use of a realistic potential, the $^6$He momentum
distribution exhibits a dip around 2 fm$^{-1}$ characteristic of $S$-wave
motion. In contrast to this, the $^6$Li momentum distribution is very similar
to that of the deuteron; no dip appears because it is filled with the $D$-wave
component arising from the tensor force.
|
arxiv topic:nucl-th
|
arxiv_dataset-22704.2201
|
Arabic Speech Recognition System using CMU-Sphinx4
cs.CL cs.AI
In this paper we present the creation of an Arabic version of Automated
Speech Recognition System (ASR). This system is based on the open source
Sphinx-4, from the Carnegie Mellon University. Which is a speech recognition
system based on discrete hidden Markov models (HMMs). We investigate the
changes that must be made to the model to adapt Arabic voice recognition.
Keywords: Speech recognition, Acoustic model, Arabic language, HMMs,
CMUSphinx-4, Artificial intelligence.
|
arxiv topic:cs.CL cs.AI
|
arxiv_dataset-23704.2301
|
Enhanced sensitivity to time-variation of m_p/m_e in the inversion
spectrum of ammonia
astro-ph hep-ph physics.atom-ph physics.space-ph
We calculate the sensitivity of the inversion spectrum of ammonia to possible
time-variation of the ratio of the proton mass to the electron mass,
mu=m_p/m_e. For the inversion transition (lambda= 1.25 cm^{-1}) the relative
frequency shift is significantly enhanced: delta(omega)/omega=-4.46,
delta(mu)/mu. This enhancement allows one to increase sensitivity to the
time-variation of mu using NH_3 spectra for high redshift objects. We use
published data on microwave spectra of the object B0218+357 to place the limit
delta(mu)/mu =(0.6 +/- 1.9) 10^{-6} at redshift z=0.6847; this limit is several
times better than the limits obtained by different methods and may be
significantly improved. Assuming linear time dependence we obtain
dot{mu}/mu=(-1 +/- 3) 10^{-16} yr^{-1}.
|
arxiv topic:astro-ph hep-ph physics.atom-ph physics.space-ph
|
arxiv_dataset-24704.2401
|
Suppressed dependence of polarization on epitaxial strain in highly
polar ferroelectrics
cond-mat.mtrl-sci
A combined experimental and computational investigation of coupling between
polarization and epitaxial strain in highly polar ferroelectric
PbZr_0.2Ti_0.8O_3 (PZT) thin films is reported. A comparison of the properties
of relaxed (tetragonality c/a = 1.05) and highly-strained (c/a = 1.09)
epitaxial films shows that polarization, while being amongst the highest
reported for PZT or PbTiO_3 in either film or bulk forms (P_r = 82
microC/cm^2), is almost independent of the epitaxial strain. We attribute this
behavior to a suppressed sensitivity of the A-site cations to epitaxial strain
in these Pb-based perovskites, where the ferroelectric displacements are
already large, contrary to the case of less polar perovskites, such as BaTiO_3.
In the latter case, the A-site cation (Ba) and equatorial oxygen displacements
can lead to substantial polarization increases.
|
arxiv topic:cond-mat.mtrl-sci
|
arxiv_dataset-25704.2501
|
Competing itinerant and localized states in strongly correlated BaVS$_3$
cond-mat.str-el cond-mat.mtrl-sci
The electronic structure of the quasi-lowdimensional vanadium sulfide \bavs3
is investigated for the different phases above the magnetic ordering
temperature. By means of density functional theory and its combination with
dynamical-mean field theory, we follow the evolution of the relevant low-energy
electronic states on cooling. Hence we go in the metallic regime from the room
temperature hexagonal phase to the orthorhombic phase after the first
structural transition, and close with the monoclinic insulating phase below the
metal-insulator transition. Due to the low symmetry and expected intersite
correlations, the latter phase is treated within cellular dynamical mean-field
theory. It is generally discussed how the intriguing interplay between
band-structure and strong-correlation effects leads to the stabilization of the
various electronic phases with decreasing temperature.
|
arxiv topic:cond-mat.str-el cond-mat.mtrl-sci
|
arxiv_dataset-26704.2601
|
GEMS: Galaxy fitting catalogues and testing parametric galaxy fitting
codes
astro-ph
In the context of measuring structure and morphology of intermediate redshift
galaxies with recent HST/ACS surveys, we tune, test, and compare two widely
used fitting codes (GALFIT and GIM2D) for fitting single-component Sersic
models to the light profiles of both simulated and real galaxy data. We find
that fitting accuracy depends sensitively on galaxy profile shape. Exponential
disks are well fit with Sersic models and have small measurement errors,
whereas fits to de Vaucouleurs profiles show larger uncertainties owing to the
large amount of light at large radii. We find that both codes provide reliable
fits and little systematic error, when the effective surface brightness is
above that of the sky. Moreover, both codes return errors that significantly
underestimate the true fitting uncertainties, which are best estimated with
simulations. We find that GIM2D suffers significant systematic errors for
spheroids with close companions owing to the difficulty of effectively masking
out neighboring galaxy light; there appears to be no work around to this
important systematic in GIM2D's current implementation. While this crowding
error affects only a small fraction of galaxies in GEMS, it must be accounted
for in the analysis of deeper cosmological images or of more crowded fields
with GIM2D. In contrast, GALFIT results are robust to the presence of neighbors
because it can simultaneously fit the profiles of multiple companions thereby
deblending their effect on the fit to the galaxy of interest. We find GALFIT's
robustness to nearby companions and factor of >~20 faster runtime speed are
important advantages over GIM2D for analyzing large HST/ACS datasets. Finally
we include our final catalog of fit results for all 41,495 objects detected in
GEMS.
|
arxiv topic:astro-ph
|
arxiv_dataset-27704.2701
|
Twisted Dirac Operators over Quantum Spheres
math.QA math-ph math.MP
We construct new families of spectral triples over quantum spheres, with a
particular attention focused on the standard Podles quantum sphere and twisted
Dirac operators.
|
arxiv topic:math.QA math-ph math.MP
|
arxiv_dataset-28704.2801
|
Continuous family groupoids
math.KT
In this paper, we define and investigate the properties of continuous family
groupoids. This class of groupoids is necessary for investigating the groupoid
index theory arising from the equivariant Atiyah-Singer index theorem for
families, and is also required in noncommutative geometry. The class includes
that of Lie groupoids, and the paper shows that, like Lie groupoids, continuous
family groupoids always admit (an essentially unique) continuous left Haar
system of smooth measures. We also show that the action of a continuous family
groupoid $G$ on a continuous family $G$-space fibered over another continuous
family $G$-space $Y$ can always be regarded as an action of the continuous
family groupoid $G*Y$ on an ordinary $G*Y$-space.
|
arxiv topic:math.KT
|
arxiv_dataset-29704.2901
|
On weakly convex star-shaped polyhedra
math.MG math.DG
Weakly convex polyhedra which are star-shaped with respect to one of their
vertices are infinitesimally rigid. This is a partial answer to the question
whether every decomposable weakly convex polyhedron is infinitesimally rigid.
The proof uses a recent result of Izmestiev on the geometry of convex caps.
|
arxiv topic:math.MG math.DG
|
arxiv_dataset-30704.3001
|
Multidimensional supernova simulations with approximative neutrino
transport. II. Convection and the advective-acoustic cycle in the supernova
core
astro-ph
By 2D hydrodynamic simulations including a detailed equation of state and
neutrino transport, we investigate the interplay between different non-radial
hydrodynamic instabilities that play a role during the postbounce accretion
phase of collapsing stellar cores. The convective mode of instability, which is
driven by negative entropy gradients caused by neutrino heating or by time
variations of the shock strength, can be identified clearly by the development
of typical Rayleigh-Taylor mushrooms. However, in cases where the gas in the
postshock region is rapidly advected towards the gain radius, the growth of
such a buoyancy instability can be suppressed. In such a situation the shocked
flow nevertheless can develop non-radial asymmetry with an oscillatory growth
of the amplitude. This phenomenon has been termed ``standing accretion shock
instability'' (SASI). It is shown here that the SASI oscillations can trigger
convective instability and like the latter they lead to an increase of the
average shock radius and of the mass in the gain layer. Both hydrodynamic
instabilities in combination stretch the advection time of matter through the
neutrino-heating layer and thus enhance the neutrino energy deposition in
support of the neutrino-driven explosion mechanism. A rapidly contracting and
more compact nascent NS turns out to be favorable for explosions, because the
accretion luminosity and neutrino heating are larger and the growth rate of the
SASI is higher. Moreover, we show that the oscillation period of the SASI and a
variety of other features in our simulations agree with estimates for the
advective-acoustic cycle (AAC), in which perturbations are carried by the
accretion flow from the shock to the neutron star and pressure waves close an
amplifying global feedback loop. (abridged)
|
arxiv topic:astro-ph
|
arxiv_dataset-31704.3101
|
A new candidate for non-strangeness pentaquarks: N*(1675)
hep-ph
We study a new nucleon resonance from eta photoproduction, which was observed
at sqrt{s}=1675 MeV with a narrow decay width (~10 MeV) by the Tohoku LNS group
as well as the GRAAL collaboration. Using an effective Lagrangian approach, we
compute differential cross sections for the eta photoproduction. In addition to
N*(1675,1/2+-,3/2+-), we employ six other nucleon resonances, i.e.
N*(1520,1535,1650,1675,1710,1720) and vector meson exchanges which are the most
relevant ones to this reaction process. As a result, we can reproduce the GRAAL
data qualitatively well and observe obvious isospin asymmetry between the
transition magnetic moments of N*(1675): mu_{gamma nn*} >> mu_{gamma pp*},
which indicates that the newly found nucleon resonance may be identified as a
non-strange pentaquark state.
|
arxiv topic:hep-ph
|
arxiv_dataset-32704.3201
|
Assisted chaotic inflation in brane-world cosmology
hep-ph
Assisted chaotic inflation in brane cosmology is discussed. We work in the
framework of Randall-Sundrum (RS) II model, in which adopting the RS condition
the only parameter is the five-dimensional Planck mass. Using the scalar
spectral index and the amplitude of scalar perturbations we determine both the
mass of the scalar fields responsible for inflation and the fundamental Planck
mass of the higher-dimensional theory. We find that the mass of the scalars has
the typical value of the inflaton mass in chaotic inflation ($M_I \sim 10^{13}$
GeV) and that the five-dimensional Planck mass is very close to the GUT (Grand
Unified Theories) scale ($M_5 \sim (10^{16}-10^{17})$ GeV). Furthermore, no
matter how many scalar fields we use it is not possible to have chaotic
inflation with field values below the fundamental Planck mass.
|
arxiv topic:hep-ph
|
arxiv_dataset-33704.3301
|
Looking beyond the horizon
hep-th astro-ph gr-qc
In this short talk we review our results from the paper hep-th/0604075 with
the main stress on the issues of causality and acoustic metric in eikonal
approximation. In addition we correct the formula for the redshift of sound
signals from our original work. We show that, if there exists a special kind of
Born-Infeld type scalar field, then one can send information from inside a
black hole. This information is encoded in perturbations of the field
propagating in non-trivial scalar field backgrounds, which serve as a "new
ether". Although the action of the theory is manifestly Lorentz-invariant the
non-trivial solutions break this symmetry spontaneously, allowing, the
superluminal propagation of perturbations with respect to this "new ether". We
found the stationary solution for background, which describes the accretion of
the scalar field onto a black hole. Examining the propagation of small
perturbations around this solution we show that the signals emitted inside the
Schwarzschild horizon can reach an observer located outside the black hole.
Thus the accreting field forms a hydrodynamical analog of a black hole whose
horizon is inside of the gravitational black hole drawing in the scalar field.
|
arxiv topic:hep-th astro-ph gr-qc
|
arxiv_dataset-34704.3401
|
Harmonic Generation from Laser-Irradiated Clusters
physics.plasm-ph physics.optics
The harmonic emission from cluster nanoplasmas subject to short, intense
infrared laser pulses is analyzed by means of particle-in-cell simulations. A
pronounced resonant enhancement of the low-order harmonic yields is found when
the Mie plasma frequency of the ionizing and expanding cluster resonates with
the respective harmonic frequency. We show that a strong, nonlinear resonant
coupling of the cluster electrons with the laser field inhibits coherent
electron motion, suppressing the emitted radiation and restricting the spectrum
to only low-order harmonics. A pump-probe scheme is suggested to monitor the
ionization dynamics of the expanding clusters.
|
arxiv topic:physics.plasm-ph physics.optics
|
arxiv_dataset-35704.3501
|
Conception d'un banc d'essais d\'ecisionnel
cs.DB
We present in this paper a new benchmark for evaluating the performances of
data warehouses. Benchmarking is useful either to system users for comparing
the performances of different systems, or to system engineers for testing the
effect of various design choices. While the TPC (Transaction Processing
Performance Council) standard benchmarks address the first point, they are not
tuneable enough to address the second one. Our Data Warehouse Engineering
Benchmark (DWEB) allows to generate various ad-hoc synthetic data warehouses
and workloads. DWEB is fully parameterized. However, two levels of
parameterization keep it easy to tune. Since DWEB mainly meets engineering
benchmarking needs, it is complimentary to the TPC standard benchmarks, and not
a competitor. Finally, DWEB is implemented as a Java free software that can be
interfaced with most existing relational database management systems.
|
arxiv topic:cs.DB
|
arxiv_dataset-36704.3601
|
Investigations of the Non-Linear LMC Cepheid Period-Luminosity Relation
with Testimator and Schwarz Information Criterion Methods
astro-ph
In this paper, we investigate the linearity versus non-linearity of the Large
Magellanic Cloud (LMC) Cepheid period-luminosity (P-L) relation using two
statistical approaches not previously applied to this problem: the testimator
method and the Schwarz Information Criterion (SIC). The testimator method is
extended to multiple stages for the first time, shown to be unbiased and the
variance of the estimated slope can be proved to be smaller than the standard
slope estimated from linear regression theory. The Schwarz Information
Criterion (also known as the Bayesian Information Criterion) is more
conservative than the Akaike Information Criterion and tends to choose lower
order models. By using simulated data sets, we verify that these statistical
techniques can be used to detect intrinsically linear and/or non-linear P-L
relations. These methods are then applied to independent LMC Cepheid data sets
from the OGLE project and the MACHO project, respectively. Our results imply
that there is a change of slope in longer period ranges for all of the data
sets. This strongly supports previous results, obtained from independent
statistical tests, that the observed LMC P-L relation is non-linear with a
break period at/around 10 days.
|
arxiv topic:astro-ph
|
arxiv_dataset-37704.3701
|
Comment on ``Enhanced transmission of light through a gold film due to
excitation of standing surface-plasmon Bloch waves"
physics.optics
The purpose of this comment is first to correct a misapprehension of the role
played by composite wave diffraction on surface-wave generation at
subwavelength structures and second to point out that periodic Bloch structures
are unnecessary for the efficient production of the surface plasmon polariton
(SPP) guided mode either as traveling or standing waves. Guided surface waves
originate from simple slit or groove edges illuminated under normal incidence,
and one-dimensional (1-D) surface cavities from these standing waves are easily
realized.
|
arxiv topic:physics.optics
|
arxiv_dataset-38704.3801
|
An annular gap acceleration model for $\gamma$-ray emission of pulsars
astro-ph
If the binding energy of the pulsar's surface is not so high (the case of a
neutron star), both the negative and positive charges will flow out freely from
the surface of the star. The annular free flow model for $\gamma$-ray emission
of pulsars is suggested in this paper. It is emphasized that: (1). Two kinds of
acceleration regions (annular and core) need to be taken into account. The
annular acceleration region is defined by the magnetic field lines that cross
the null charge surface within the light cylinder. (2). If the potential drop
in the annular region of a pulsar is high enough (normally the cases of young
pulsars), charges in both the annular and the core regions could be accelerated
and produce primary gamma-rays. Secondary pairs are generated in both regions
and stream outwards to power the broadband radiations. (3). The potential drop
in the annular region grows more rapidly than that in the core region. The
annular acceleration process is a key point to produce wide emission beams as
observed. (4). The advantages of both the polar cap and outer gap models are
retained in this model. The geometric properties of the $\gamma$-ray emission
from the annular flow is analogous to that presented in a previous work by Qiao
et al., which match the observations well. (5). Since charges with different
signs leave the pulsar through the annular and the core regions, respectively,
the current closure problem can be partially solved.
|
arxiv topic:astro-ph
|
arxiv_dataset-39704.3901
|
Existence and symmetry of minimizers for nonconvex radially symmetric
variational problems
math.CA
Nonconvex functionals with spherical symmetry are studied. Existence of one
and radial symmetry of all global minimizers is shown with an approach based on
convex relaxation.
|
arxiv topic:math.CA
|
arxiv_dataset-40704.4001
|
Warping and Supersymmetry Breaking
hep-th
We analyze supersymmetry breaking by anti-self-dual flux in the deformed
conifold. This theory has been argued to be a dual realization of susy breaking
by antibranes. As such, one might expect it to lead to a hierarchically small
breaking scale, but only if the warp factor is taken into account. We verify
this by explicitly computing the warp-modified moduli space metric. This leads
to a new term, with a power-like divergence at the conifold point, which lowers
the breaking scale. We finally point out various puzzles regarding the gauge
theory interpretation of these results.
|
arxiv topic:hep-th
|
arxiv_dataset-41705.0098
|
Gauss map on the theta divisor and Green's functions
math.AG
In an earlier paper we constructed a Cartier divisor on the theta divisor of
a principally polarised abelian variety whose support is precisely the
ramification locus of the Gauss map. In this note we discuss a Green's function
associated to this locus. For jacobians we relate this Green's function to the
canonical Green's function of the corresponding Riemann surface.
|
arxiv topic:math.AG
|
arxiv_dataset-42705.0198
|
Two Scenarios of Breaking Chaotic Phase Synchronization
nlin.CD
Two types of phase synchronization (accordingly, two scenarios of breaking
phase synchronization) between coupled stochastic oscillators are shown to
exist depending on the discrepancy between the control parameters of
interacting oscillators, as in the case of classical synchronization of
periodic oscillators. If interacting stochastic oscillators are weakly detuned,
the phase coherency of the attractors persists when phase synchronization
breaks. Conversely, if the control parameters differ considerably, the chaotic
attractor becomes phase-incoherent under the conditions of phase
synchronization break.
|
arxiv topic:nlin.CD
|
arxiv_dataset-43705.0298
|
J1128+592: a highly variable IDV source
astro-ph
Short time-scale radio variations of compact extragalactic radio quasars and
blazars known as IntraDay Variability (IDV) can be explained in at least some
sources as a propagation effect; the variations are interpreted as
scintillation of radio waves in the turbulent interstellar medium of the Milky
Way. One of the most convincing observational arguments in favor of a
propagation-induced variability scenario is the observed annual modulation in
the characteristic time scale of the variation due to the Earth's orbital
motion. So far there are only two sources known with a well-constrained
seasonal cycle. Annual modulation has been proposed for a few other less
well-documented objects. However, for some other IDV sources source-intrinsic
structural variations which cause drastic changes in the variability time scale
were also suggested. J1128+592 is a recently discovered, highly variable IDV
source. Previous, densely time-sampled flux-density measurements with the
Effelsberg 100-m radio telescope (Germany) and the Urumqi 25-m radio telescope
(China), strongly indicate an annual modulation of the time scale. The most
recent 4 observations in 2006/7, however, do not fit well to the annual
modulation model proposed before. In this paper, we investigate a possible
explanation of this discrepancy.
|
arxiv topic:astro-ph
|
arxiv_dataset-44705.0398
|
Search for B0->phiK+pi- Decays with Large K+pi- Invariant Mass
hep-ex
Motivated by the polarization anomaly in the B->phi(1020)K*(892) decay, we
extend our search for other K* final states in the decay B0->phi(1020)K^*0 with
the K*0->K+pi- invariant mass above 1.6 GeV. The final states considered
include the K*(1680)0, K3*(1780)0, K4*(2045)0, and a Kpi spin-zero nonresonant
component. We also search for B0->phiDbar0 decay with the same final state. The
analysis is based on a sample of about 384 million BBbar pairs recorded with
the BABAR detector. We place upper limits on the branching fractions
BR(B0->phiK*(1680)0)<3.5*10^-6, BR(B0->phiK3*(1780)0)<2.7*10^-6,
BR(B0->phiK4*(2045)0)<15.3*10^-6, and BR(B0->phiDbar0)<11.7*10^-6 at 90% C.L.
The nonresonant contribution is consistent with the measurements in the lower
invariant mass range.
|
arxiv topic:hep-ex
|
arxiv_dataset-45705.0498
|
Electron Doping of Cuprates via Interfaces with Manganites
cond-mat.str-el cond-mat.supr-con
The electron doping of undoped high-$T_c$ cuprates via the transfer of charge
from manganites (or other oxides) using heterostructure geometries is here
theoretically discussed. This possibility is mainly addressed via a detailed
analysis of photoemission and diffusion voltage experiments, which locate the
Fermi level of manganites above the bottom of the upper Hubbard band of some
cuprate parent compounds. A diagram with the relative location of Fermi levels
and gaps for several oxides is presented. The procedure discussed here is
generic, allowing for the qualitative prediction of the charge flow direction
at several oxide interfaces. The addition of electrons to antiferromagnetic Cu
oxides may lead to a superconducting state at the interface with minimal
quenched disorder. Model calculations using static and dynamical mean-field
theory, supplemented by a Poisson equation formalism to address charge
redistribution at the interface, support this view. The magnetic state of the
manganites could be antiferromagnetic or ferromagnetic. The former is better to
induce superconductivity than the latter, since the spin-polarized charge
transfer will be detrimental to singlet superconductivity. It is concluded that
in spite of the robust Hubbard gaps, the electron doping of undoped cuprates at
interfaces appears possible, and its realization may open an exciting area of
research in oxide heterostructures.
|
arxiv topic:cond-mat.str-el cond-mat.supr-con
|
arxiv_dataset-46705.0598
|
Magnetic Evolution and Temperature Variation in a Coronal Hole
astro-ph
We have explored the magnetic flux evolution and temperature variation in a
coronal-hole region, using Big Bear Solar Observatory (BBSO) deep magnetograms
and {\it SOHO}/EIT images observed from 2005 October 10 to 14. For comparison,
we also investigated a neighboring quiet region of the Sun. The coronal hole
evolved from its mature stage to its disappearance during the observing period.
We have obtained the following results: (1) When the coronal hole was well
developed on October 10, about 60 % of the magnetic flux was positive. The EUV
brightness was 420 counts pixel$^{-1}$, and the coronal temperature, estimated
from the line ratio of the EIT 195 {\AA} and 171 {\AA} images, was 1.07 MK. (2)
On October 14, when the coronal hole had almost disappeared, 51 % of the
magnetic flux was positive, the EUV radiance was 530 counts pixel$^{-1}$, and
the temperature was 1.10 MK. (3) In the neighboring quiet region, the fraction
of positive flux varied between 0.49 and 0.47. The EUV brightness displayed an
irregular variation, with a mean value of 870 counts pixel$^{-1}$. The
temperature was almost constant at 1.11 MK during the five-day observation. Our
results demonstrate that in a coronal hole less imbalance of the magnetic flux
in opposite polarities leads to stronger EUV brightness and higher coronal
temperatures.
|
arxiv topic:astro-ph
|
arxiv_dataset-47705.0698
|
Signed q-Analogs of Tornheim's Double Series
math.NT math.CA
We introduce signed q-analogs of Tornheim's double series, and evaluate them
in terms of double q-Euler sums. As a consequence, we provide explicit
evaluations of signed and unsigned Tornheim double series, and correct some
mistakes in the literature.
|
arxiv topic:math.NT math.CA
|
arxiv_dataset-48705.0798
|
On the structure of positive maps between matrix algebras
math.FA math.OA
A partial description of the structure of positive unital maps $\phi:
M_2(\bC) \to M_{n+1}(\bC)$ ($n\geq 2$) is given.
|
arxiv topic:math.FA math.OA
|
arxiv_dataset-49705.0898
|
Testing anthropic predictions for Lambda and the CMB temperature
astro-ph
It has been claimed that the observed magnitude of the vacuum energy density
is consistent with the distribution predicted in anthropic models, in which an
ensemble of universes is assumed. This calculation is revisited, without making
the assumption that the CMB temperature is known, and considering in detail the
possibility of a recollapsing universe. New accurate approximations for the
growth of perturbations and the mass function of dark haloes are presented.
Structure forms readily in the recollapsing phase of a model with negative
Lambda, so collapse fraction alone cannot forbid Lambda from being large and
negative. A negative Lambda is disfavoured only if we assume that formation of
observers can be neglected once the recollapsing universe has heated to T > 8
K. For the case of positive Lambda, however, the current universe does occupy a
extremely typical position compared to the predicted distribution on the
Lambda-T plane. Contrasting conclusions can be reached if anthropic arguments
are applied to the curvature of the universe, and we discuss the falsifiability
of this mode of anthropic reasoning.
|
arxiv topic:astro-ph
|
arxiv_dataset-50705.0998
|
The alternating sign matrix polytope
math.CO
We define the alternating sign matrix polytope as the convex hull of nxn
alternating sign matrices and prove its equivalent description in terms of
inequalities. This is analogous to the well known result of Birkhoff and von
Neumann that the convex hull of the permutation matrices equals the set of all
nonnegative doubly stochastic matrices. We count the facets and vertices of the
alternating sign matrix polytope and describe its projection to the
permutohedron as well as give a complete characterization of its face lattice
in terms of modified square ice configurations. Furthermore we prove that the
dimension of any face can be easily determined from this characterization.
|
arxiv topic:math.CO
|
arxiv_dataset-51705.1098
|
Supersymmetric Black Rings on Eguchi-Hanson Space
hep-th
We construct new supersymmetric black ring solutions on the Eguchi-Hanson
base space as solutions of five-dimensional minimal supergravity. The solutions
have the same two angular momentum components and the asymptotic structure on
timeslices is asymptotically locally Euclidean. The S^1-direction of the black
ring is along the equator on a S^2-bolt on the Eguchi-Hanson space. We also
investigate the limit to a black hole, which describes the BMPV black hole with
the topology of the lens space L(2;1)=S^3/Z_2.
|
arxiv topic:hep-th
|
arxiv_dataset-52705.1198
|
Measured oscillations of the velocity and temperature fields in
turbulent Rayleigh-B\'{e}nard convection in a rectangular cell
physics.flu-dyn
Temperature and velocity oscillations have been found in a rectangular
Rayleigh-B\'{e}nard convection cell, in which one large scale convection roll
exists. At $Ra=8.9 \times 10^{11}$ and $Pr=4$, temperature oscillation can be
observed in most part of the system and the oscillation period remains almost
constant, $t_T = 74 \pm 2$ seconds. Velocity oscillation can only be found in
its horizontal component, $v_y$ (perpendicular to large scale circulation
plane), near the cell sidewall, its oscillation period is also constant, $t_T =
65 \pm 2$ seconds, at these positions. Temperature and velocity oscillations
have different Ra dependence, which are respectively indicated by Peclect
number $Pe_T = 0.55Ra^{0.47}$ and $Pe_v = 0.28Ra^{0.50}$ . In comparison to the
case of cylindrical cell, we find that the velocity oscillation is affected by
the system geometry.
|
arxiv topic:physics.flu-dyn
|
arxiv_dataset-53705.1298
|
Mykyta the Fox and networks of language
physics.data-an physics.soc-ph
The results of quantitative analysis of word distribution in two fables in
Ukrainian by Ivan Franko: "Mykyta the Fox" and "Abu-Kasym's slippers" are
reported. Our study consists of two parts: the analysis of frequency-rank
distributions and the application of complex networks theory. The analysis of
frequency-rank distributions shows that the text sizes are enough to observe
statistical properties. The power-law character of these distributions (Zipf's
law) holds in the region of rank variable r=20 - 3000 with an exponent
$\alpha\simeq 1$. This substantiates the choice of the above texts to analyse
typical properties of the language complex network on their basis. Besides, an
applicability of the Simon model to describe non-asymptotic properties of word
distributions is evaluated.
In describing language as a complex network, usually the words are associated
with nodes, whereas one may give different meanings to the network links. This
results in different network representations. In the second part of the paper,
we give different representations of the language network and perform
comparative analysis of their characteristics. Our results demonstrate that the
language network of Ukrainian is a strongly correlated scale-free small world.
Empirical data obtained may be useful for theoretical description of language
evolution.
|
arxiv topic:physics.data-an physics.soc-ph
|
arxiv_dataset-54705.1398
|
Experimental demonstration of Shor's algorithm with quantum entanglement
quant-ph
Shor's powerful quantum algorithm for factoring represents a major challenge
in quantum computation and its full realization will have a large impact on
modern cryptography. Here we implement a compiled version of Shor's algorithm
in a photonic system using single photons and employing the non-linearity
induced by measurement. For the first time we demonstrate the core processes,
coherent control, and resultant entangled states that are required in a
full-scale implementation of Shor's algorithm. Demonstration of these processes
is a necessary step on the path towards a full implementation of Shor's
algorithm and scalable quantum computing. Our results highlight that the
performance of a quantum algorithm is not the same as performance of the
underlying quantum circuit, and stress the importance of developing techniques
for characterising quantum algorithms.
|
arxiv topic:quant-ph
|
arxiv_dataset-55705.1498
|
ROXA: a new multi-frequency selected large sample of blazars with SDSS
and 2dF optical spectroscopy
astro-ph
Context. Although Blazars are a small fraction of the overall AGN population
they are expected to be the dominant population of extragalactic sources in the
hard X-ray and gamma-ray bands and have been shown to be the largest
contaminant of CMB fluctuation maps. So far the number of known blazars is of
the order of several hundreds, but the forthcoming AGILE, GLAST and Planck
space observatories will detect several thousand of objects of this type. Aims.
In preparation for these missions it is necessary to identify new samples of
blazars to study their multi-frequency characteristics and statistical
properties. Methods. We compiled a sample of objects with blazar-like
properties via a cross-correlation between large radio (NVSS, ATCAPMN) and X-
ray surveys (RASS) using the SDSS-DR4 and 2dF survey data to spectroscopically
identify our candidates and test the validity of the selection method. Results.
We present the Radio - Optical - X-ray catalog built at ASDC (ROXA), a list of
816 objects among which 510 are confirmed blazars. Only 19% of the candidates
turned out to be certainly non-blazars demonstrating the high efficiency of our
selection method. Conclusions. Our catalog includes 173 new blazar
identifications, or about 10% of all presently known blazars. The relatively
high flux threshold in the X-ray energy band (given by the RASS survey)
preferentially selects objects with high fx / fr ratio leading to the discovery
of new High Energy Peaked BL Lac (HBLs). Our catalog therefore includes many
new potential targets for GeV-TeV observations.
|
arxiv topic:astro-ph
|
arxiv_dataset-56705.1598
|
Application of Girsanov Theorem to Particle Filtering of Discretely
Observed Continuous-Time Non-Linear Systems
stat.ME stat.CO
This article considers the application of particle filtering to
continuous-discrete optimal filtering problems, where the system model is a
stochastic differential equation, and noisy measurements of the system are
obtained at discrete instances of time. It is shown how the Girsanov theorem
can be used for evaluating the likelihood ratios needed in importance sampling.
It is also shown how the methodology can be applied to a class of models, where
the driving noise process is lower in the dimensionality than the state and
thus the laws of state and noise are not absolutely continuous.
Rao-Blackwellization of conditionally Gaussian models and unknown static
parameter models is also considered.
|
arxiv topic:stat.ME stat.CO
|
arxiv_dataset-57705.1698
|
Hives and the fibres of the convolution morphism
math.AG math.RT
By the geometric Satake correspondence, the number of components of certain
fibres of the affine Grassmannian convolution morphism equals the tensor
product multiplicity for representations of the Langlands dual group. On the
other hand, in the case of GL_n, combinatorial objects called hives also count
tensor product multiplicities. The purpose of this paper is to give a simple
bijection between hives and the components of these fibres. In particular, we
give a description of the individual components. We also describe a conjectural
generalization involving the octahedron recurrence.
|
arxiv topic:math.AG math.RT
|
arxiv_dataset-58705.1798
|
Amplitude Analysis of the B+- ->phi K*(892)+- Decay
hep-ex
We perform an amplitude analysis of B+- -> phi(1020) K*(892)+- decay with a
sample of about 384 million BBbar pairs recorded with the BABAR detector.
Overall, twelve parameters are measured, including the fractions of
longitudinal f_L and parity-odd transverse f_perp amplitudes, branching
fraction, strong phases, and six parameters sensitive to CP-violation. We use
the dependence on the Kpi invariant mass of the interference between the JP=1-
and 0+ Kpi components to resolve the discrete ambiguity in the determination of
the strong and weak phases. Our measurements of f_L=0.49+-0.05+-0.03,
f_perp=0.21+-0.05+-0.02, and the strong phases point to the presence of a
substantial helicity-plus amplitude from a presently unknown source.
|
arxiv topic:hep-ex
|
arxiv_dataset-59705.1898
|
Experimental test of the no signaling theorem
quant-ph
In 1981 N. Herbert proposed a gedanken experiment in order to achieve by the
''First Laser Amplified Superluminal Hookup'' (FLASH) a faster than light
communication (FTL) by quantum nonlocality. The present work reports the first
experimental realization of that proposal by the optical parametric
amplification of a single photon belonging to an entangled EPR pair into an
output field involving 5 x 10^3 photons. A thorough theoretical and
experimental analysis explains in general and conclusive terms the precise
reasons for the failure of the FLASH program as well as of any similar FTL
proposals.
|
arxiv topic:quant-ph
|
arxiv_dataset-60705.1998
|
Hamiltonian reductions of free particles under polar actions of compact
Lie groups
math-ph math.DG math.MP nlin.SI
Classical and quantum Hamiltonian reductions of free geodesic systems of
complete Riemannian manifolds are investigated. The reduced systems are
described under the assumption that the underlying compact symmetry group acts
in a polar manner in the sense that there exist regularly embedded, closed,
connected submanifolds meeting all orbits orthogonally in the configuration
space. Hyperpolar actions on Lie groups and on symmetric spaces lead to
families of integrable systems of spin Calogero-Sutherland type.
|
arxiv topic:math-ph math.DG math.MP nlin.SI
|
arxiv_dataset-61705.2098
|
Kolkata Restaurant Problem as a generalised El Farol Bar Problem
physics.soc-ph q-fin.ST
Generalisation of the El Farol bar problem to that of many bars here leads to
the Kolkata restaurant problem, where the decision to go to any restaurant or
not is much simpler (depending on the previous experience of course, as in the
El Farol bar problem). This generalised problem can be exactly analysed in some
limiting cases discussed here. The fluctuation in the restaurant service can be
shown to have precisely an inverse cubic behavior, as widely seen in the stock
market fluctuations.
|
arxiv topic:physics.soc-ph q-fin.ST
|
arxiv_dataset-62705.2198
|
Charmonium at high temperature in two-flavor QCD
hep-lat hep-ph nucl-th
We compute charmonium spectral functions in 2-flavor QCD on anisotropic
lattices using the maximum entropy method. Our results suggest that the S-waves
(J/psi and eta_c) survive up to temperatures close to 2Tc, while the P-waves
(chi_c0 and chi_c1) melt away below 1.2Tc.
|
arxiv topic:hep-lat hep-ph nucl-th
|
arxiv_dataset-63705.2298
|
Local Sentences and Mahlo Cardinals
math.LO
Local sentences were introduced by J.-P. Ressayre who proved certain
remarkable stretching theorems establishing the equivalence between the
existence of finite models for these sentences and the existence of some
infinite well ordered models. Two of these stretching theorems were only proved
under certain large cardinal axioms but the question of their exact
(consistency) strength was left open in [O. Finkel and J.-P. Ressayre,
Stretchings, Journal of Symbolic Logic, Volume 61 (2), 1996, p. 563-585 ].
Here, we solve this problem, using a combinatorial result of J. H. Schmerl. In
fact, we show that the stretching principles are equivalent to the existence of
n-Mahlo cardinals for appropriate integers n. This is done by proving first
that for each integer n, there is a local sentence phi_n which has well ordered
models of order type alpha, for every infinite ordinal alpha > omega which is
not an n-Mahlo cardinal.
|
arxiv topic:math.LO
|
arxiv_dataset-64705.2398
|
Light-shift-induced photonic nonlinearities
quant-ph
We propose a new method to produce self- and cross-Kerr photonic
nonlinearities, using light-induced Stark shifts due to the interaction of a
cavity mode with atoms. The proposed experimental set-up is considerably
simpler than in previous approaches, while the strength of the nonlinearity
obtained with a single atom is the same as in the setting based on
electromagnetically induced transparency. Furthermore our scheme can be applied
to engineer effective photonic nonlinear interactions whose strength increases
with the number of atoms coupled to the cavity mode, leading to photon-photon
interactions several orders of magnitude larger than previously considered
possible.
|
arxiv topic:quant-ph
|
arxiv_dataset-65705.2498
|
Ferromagnetism in nanoscale BiFeO3
cond-mat.mtrl-sci
A remarkably high saturation magnetization of ~0.4mu_B/Fe along with room
temperature ferromagnetic hysteresis loop has been observed in nanoscale (4-40
nm) multiferroic BiFeO_3 which in bulk form exhibits weak magnetization
(~0.02mu_B/Fe) and an antiferromagnetic order. The magnetic hysteresis loops,
however, exhibit exchange bias as well as vertical asymmetry which could be
because of spin pinning at the boundaries between ferromagnetic and
antiferromagnetic domains. Interestingly, like in bulk BiFeO_3, both the
calorimetric and dielectric permittivity data in nanoscale BiFeO_3 exhibit
characteristic features at the magnetic transition point. These features
establish formation of a true ferromagnetic-ferroelectric system with a
coupling between the respective order parameters in nanoscale BiFeO_3.
|
arxiv topic:cond-mat.mtrl-sci
|
arxiv_dataset-66705.2598
|
SuperWASP-N Extra-solar Planet Candidates Between 18hr < RA < 21hr
astro-ph
The SuperWASP-I instrument observed 6.7 million stars between 8-15 mag from
La Palma during the 2004 May-September season. Our transit-hunting algorithm
selected 11,626 objects from the 184,442 stars within the range RA 18hr-21hr.
We describe our thorough selection procedure whereby catalogue information is
exploited along with careful study of the SuperWASP data to filter out, as far
as possible, transit mimics. We have identified 35 candidates which we
recommend for follow-up observations.
|
arxiv topic:astro-ph
|
arxiv_dataset-67705.2698
|
Computed tomography image reconstruction from only two projections
physics.data-an physics.comp-ph
English: This paper concerns the image reconstruction from a few projections
in Computed Tomography (CT). The main objective of this paper is to show that
the problem is so ill posed that no classical method, such as analytical
methods based on inverse Radon transform, nor the algebraic methods such as
Least squares (LS) or regularization theory can give satisfactory result. As an
example, we consider in detail the case of image reconstruction from two
horizontal and vertical projections. We then show how a particular composite
Markov modeling and the Bayesian estimation framework can possibly propose
satisfactory solutions to the problem. For demonstration and educational
purpose a set of Matlab programs are given for a live presentation of the
results.
-----
French: Ce travail, \`a but p\'edagogique, pr\'esente le probl\`eme inverse
de la reconstruction d'image en tomographie X lorsque le nombre des projections
est tr\`es limit\'e. voir le texte en Anglais et en Fran\c{c}ais.
|
arxiv topic:physics.data-an physics.comp-ph
|
arxiv_dataset-68705.2798
|
A perturbative approach to a class of Fokker-Planck equations
math-ph cond-mat.other math.AP math.MP
In this paper we present a direct perturbative method to solving certain
Fokker-Planck equations, which have constant diffusion coefficients and some
small parameters in the drift coefficients. The method makes use of the
connection between the Fokker-Planck and Schr\"odinger equations. Two examples
are used to illustrate the method. In the first example the drift coefficient
depends only on time but not on space. In the second example we consider the
Uhlenbeck-Ornstein process with a small drift coefficient. These examples show
that the such perturbative approach can be a useful tool to obtain approximate
solutions of Fokker-Planck equations with constant diffusion coefficients.
|
arxiv topic:math-ph cond-mat.other math.AP math.MP
|
arxiv_dataset-69705.2898
|
The robustness of the vacuum wave function and other matters for
Yang-Mills theory
hep-th
In the first part of this paper, we present a set of simple arguments to show
that the two-dimensional gauge anomaly and the (2+1)-dimensional Lorentz
symmetry determine the leading Gaussian term in the vacuum wave function of
(2+1)-dimensional Yang-Mills theory. This is to highlight the robustness of the
wave function and its relative insensitivity to the choice of regularizations.
We then comment on the correspondence with the explicit calculations done in
earlier papers. We also make some comments on the nature of the gauge-invariant
configuration space for Euclidean three-dimensional gauge fields (relevant to
(3+1)-dimensional Yang-Mills theory).
|
arxiv topic:hep-th
|
arxiv_dataset-70705.2998
|
Measurements of CKM Angle Beta from BABAR
hep-ex
We present recent results of hadronic B meson decays related to the CKM angle
beta. The data used were collected by the BABAR detector at the pepII
asymmetric-energy e+e- collider operating at the Upsilon(4S) resonance located
at the Stanford Linear Accelerator Center.
|
arxiv topic:hep-ex
|
arxiv_dataset-71705.3098
|
Chaotic motion in Kundt spacetimes
gr-qc
We demonstrate that geodesics in exact vacuum Kundt gravitational waves may
exhibit a highly complicated behaviour. In fact, as in the previously studied
case of non-homogeneous pp-waves, for specific choices of the structural
function the motion appears to be genuinely chaotic. This fact is demonstrated
by the fractal method.
|
arxiv topic:gr-qc
|
arxiv_dataset-72705.3198
|
Internal states of model isotropic granular packings. III. Elastic
properties
cond-mat.dis-nn cond-mat.mtrl-sci physics.class-ph
In this third and final paper of a series, elastic properties of numerically
simulated isotropic packings of spherical beads assembled by different
procedures and subjected to a varying confining pressure P are investigated. In
addition P, which determines the stiffness of contacts by Hertz's law, elastic
moduli are chiefly sensitive to the coordination number, the possible values of
which are not necessarily correlated with the density. Comparisons of numerical
and experimental results for glass beads in the 10kPa-10MPa range reveal
similar differences between dry samples compacted by vibrations and lubricated
packings. The greater stiffness of the latter, in spite of their lower density,
can hence be attributed to a larger coordination number. Voigt and Reuss bounds
bracket bulk modulus B accurately, but simple estimation schemes fail for shear
modulus G, especially in poorly coordinated configurations under low P.
Tenuous, fragile networks respond differently to changes in load direction, as
compared to load intensity. The shear modulus, in poorly coordinated packings,
tends to vary proportionally to the degree of force indeterminacy per unit
volume. The elastic range extends to small strain intervals, in agreement with
experimental observations. The origins of nonelastic response are discussed. We
conclude that elastic moduli provide access to mechanically important
information about coordination numbers, which escape direct measurement
techniques, and indicate further perspectives.
|
arxiv topic:cond-mat.dis-nn cond-mat.mtrl-sci physics.class-ph
|
arxiv_dataset-73705.3298
|
Bogoliubov spectrum of a cigar shaped Fermi superfluid in an optical
lattice at the BEC-BCS crossover
cond-mat.stat-mech
We study the Bogoliubov spectrum of an elongated Fermi superfluid confined in
an one-dimensional superfluid along the Bose-Einstein-condensate
(BEC)-Bardeen-Cooper-Schrieffer (BCS) crossover. We derive analytic expressions
for the sound velocity, effective mass and the Bogoliubov excitation spectrum
of the axial quasiparticles long the crossover based on the hydrodynamic
theory. Our investigation reveal interesting signatures of BEC-BCS crossover in
an optical lattice which deserve experimental investigation.
|
arxiv topic:cond-mat.stat-mech
|
arxiv_dataset-74705.3398
|
Efficient control of transient wave forms to prevent spreading
depolarizations
nlin.PS
In various neurological disorders spatio-temporal excitation patterns
constitute examples of excitable behavior emerging from pathological pathways.
During migraine, seizure, and stroke an initially localized pathological state
can temporarily spread indicating a transition from non-excitable to excitable
behavior. We investigate these transient wave forms in the generic
FitzHugh-Nagumo (FHN) system of excitable media. Our goal is to define an
efficient control minimizing the volume of invaded tissue. The general point of
such a therapeutic optimization is how to apply control theory in the framework
of structures in differential geometry by regarding parameter plane M of the
FHN system as a differential manifold endowed with a metric. We suggest to
equip M with a metric given by pharmacokinetic-pharmacodynamic models of drug
receptor interaction.
|
arxiv topic:nlin.PS
|
arxiv_dataset-75705.3498
|
Measurement of Newtonian fluid slip using a torsional ultrasonic
oscillator
physics.flu-dyn
The composite torsional ultrasonic oscillator, a versatile experimental
system, can be used to investigate slip of Newtonian fluid at a smooth surface.
A rigorous analysis of slip-dependent damping for the oscillator is presented.
Initially, the phenomenon of finite surface slip and the slip length are
considered for a half-space of Newtonian fluid in contact with a smooth,
oscillating solid surface. Definitions are revisited and clarified in light of
inconsistencies in the literature. We point out that, in general oscillating
flows, Navier's slip length b is a complex number. An intuitive velocity
discontinuity parameter of unrestricted phase is used to describe the effect of
slip on measurement of viscous shear damping. The analysis is applied to the
composite oscillator and preliminary experimental work for a 40 kHz oscillator
is presented. The Non-Slip Boundary Condition (NSBC) has been verified for a
hydrophobic surface in water to within ~60 nm of |b|=0 nm. Experiments were
carried out at shear rate amplitudes between 230 and 6800 /s, corresponding to
linear displacement amplitudes between 3.2 and 96 nm.
|
arxiv topic:physics.flu-dyn
|
arxiv_dataset-76705.3598
|
Pseudoprocesses governed by higher-order fractional differential
equations
math.PR
We study here a heat-type differential equation of order n greater than two,
in the case where the time-derivative is supposed to be fractional. The
corresponding solution can be described as the transition function of a
pseudoprocess (coinciding with the one governed by the standard,
non-fractional, equation) with a time argument T which is itself random. The
distribution of T is presented together with some features of the solution
(such as analytic expressions for its moments).
|
arxiv topic:math.PR
|
arxiv_dataset-77705.3698
|
Confining properties of QCD at finite temperature and density
hep-lat hep-ph
A disorder parameter detecting dual superconductivty of the vacuum is used as
a probe to characterize the confining properties of the phase diagram of two
color QCD at finite temperature and density. We obtain evidence for the
disappearing of dual superconductivity (deconfinement) induced by a finite
density of baryonic matter, as well as for a coincidence of this phenomenon
with the restoration of chiral symmetry both at zero and finite density. The
saturation transition induced by Pauli blocking is studied as well, and a
general warning is given about the possible effects that this unphysical
transition could have on the study of the QCD phase diagram at strong values of
the gauge coupling.
|
arxiv topic:hep-lat hep-ph
|
arxiv_dataset-78705.3798
|
Extension of the generalised inductive approach to the lace expansion:
Full proof
math.PR math-ph math.MP
This paper extends the inductive approach to the lace expansion of van der
Hofstad and Slade in order to prove Gaussian asymptotic behaviour for models
with critical dimension other than 4. The results are applied by Holmes to
study sufficiently spread-out lattice trees in dimensions d>8 and may also be
applicable to percolation in dimensions d>6.
|
arxiv topic:math.PR math-ph math.MP
|
arxiv_dataset-79705.3898
|
Quantum-like Representation of Macroscopic Configurations
quant-ph
The aim of this paper is to apply a contextual probabilistic model (in the
spirit of Mackey, Gudder, Ballentine) to represent and to generalize some
results of quantum logic about possible macroscopic quantum-like (QL)
behaviour. The crucial point is that our model provides QL-representation of
macroscopic configurations in terms of complex probability amplitudes -- wave
functions of such configurations. Thus, instead of the language of propositions
which is common in quatum logic, we use the language of wave functions which is
common in the conventional presentation of QM. We propose a quantum-like
representation algorithm, QLRA, which maps probabilistic data of any origin in
complex (or even hyperbolic) Hilbert space. On the one hand, this paper
clarifyes some questions in foundations of QM, since some rather mystical
quantum features are illustrated on the basis of behavior of macroscopic
systems. On the other hand, the approach developed in this paper may be used
e.g. in biology, sociology, or psychology. Our example of QL-representation of
hidden macroscopic configurations can find natural applications in those
domains of science.
|
arxiv topic:quant-ph
|
arxiv_dataset-80705.3998
|
Geometry of Borromean Halo Nuclei
nucl-th
We discuss the geometry of the highly quantal nuclear three-body systems
composed of a core plus two loosely bound particles. These Borromean nuclei
have no single bound two-body subsystem. Correlation plays a prominent role.
From consideration of the $B(E1)$ value extracted from electromagnetic
dissociation, in conjunction with HBT-type analysis of the two valence-halo
particles correlation, we show that an estimate of the over-all geometry can be
deduced. In particular we find that the opening angle between the two neutrons
in $^{6}$He and $^{11}$Li are, respectively, $\theta_{nn} =
{83^{\circ}}^{+20}_{-10}$ and ${66^{\circ}}^{+22}_{-18}$. These angles are
reduced by about 12% to $\theta_{nn} = {78^{\circ}}^{+13}_{-18}$ and
${58^{\circ}}^{+10}_{-14}$ if the laser spectroscopy values of the rms charge
radii are used to obtain the rms distance between the cores and the center of
mass of the two neutrons. The opening angle in the case of $^{11}$Li is more
than 20% larger than recently reported by Nakamura \cite{Nak06}. The analysis
is extended to $^{14}$Be and the two-proton Borromean nucleus $^{17}% $Ne where
complete data is still not available. Using available experimental data and
recent theoretical calculations we find, $\theta_{nn} = {64^{0}}^{+9}_{-10}$
and $\theta_{pp} = 110^{0}$, respectively.
|
arxiv topic:nucl-th
|
arxiv_dataset-81705.4098
|
Extended Holomorphic Anomaly and Loop Amplitudes in Open Topological
String
hep-th math.AG
Open topological string amplitudes on compact Calabi-Yau threefolds are shown
to satisfy an extension of the holomorphic anomaly equation of Bershadsky,
Cecotti, Ooguri and Vafa. The total topological charge of the D-brane
configuration must vanish in order to satisfy tadpole cancellation. The
boundary state of such D-branes is holomorphically captured by a Hodge
theoretic normal function. Its Griffiths' infinitesimal invariant is the
analogue of the closed string Yukawa coupling and plays the role of the
terminator in a Feynman diagram expansion for the topological string with
D-branes. The holomorphic anomaly equation is solved and the holomorphic
ambiguity is fixed for some representative worldsheets of low genus and with
few boundaries on the real quintic.
|
arxiv topic:hep-th math.AG
|
arxiv_dataset-82705.4198
|
Exotic Mott phases of the extended t--J model on the checkerboard
lattice at commensurate densities
cond-mat.str-el cond-mat.supr-con
Coulomb repulsion between electrons moving on a frustrated lattice can give
rise, at simple commensurate electronic densities, to exotic insulating phases
of matter. Such a phenomenon is illustrated using an extended t--J model on a
planar pyrochlore lattice for which the work on the quarter-filled case
[cond-mat/0702367] is complemented and extended to 1/8- and 3/8-fillings. The
location of the metal-insulator transition as a function of the Coulomb
repulsion is shown to depend strongly on the sign of the hopping. Quite
generally, the metal-insulator transition is characterized by lattice symmetry
breaking but the nature of the insulating Mott state is more complex than a
simple Charge Density Wave. Indeed, in the limit of large Coulomb repulsion,
the physics can be described in the framework of (extended) quantum
fully-packed loop or dimer models carrying extra spin degrees of freedom.
Various diagonal and off-diagonal plaquette correlation functions are computed
and the low-energy spectra are analyzed in details in order to characterize the
nature of the insulating phases. We provide evidence that, as for an electronic
density of n=1/2 (quarter-filling), the system at $n=1/4$ or $n=3/4$ exhibits
also plaquette order by forming a (lattice rotationally-invariant)
Resonating-Singlet-Pair Crystal, although with a quadrupling of the lattice
unit cell (instead of a doubling for $n=1/2$) and a 4-fold degenerate ground
state. Interestingly, qualitative differences with the bosonic analog (e.g.
known to exhibit columnar order at n=1/4) emphasize the important role of the
spin degrees of freedom in e.g. stabilizing plaquette phases w.r.t. rotational
symmetry-breaking phases.
|
arxiv topic:cond-mat.str-el cond-mat.supr-con
|
arxiv_dataset-83705.4298
|
Towards Closing the Window on Strongly Interacting Dark Matter:
Far-Reaching Constraints from Earth's Heat Flow
astro-ph hep-ph nucl-th
We point out a new and largely model-independent constraint on the dark
matter scattering cross section with nucleons, applying when this quantity is
larger than for typical weakly interacting dark matter candidates. When the
dark matter capture rate in Earth is efficient, the rate of energy deposition
by dark matter self-annihilation products would grossly exceed the measured
heat flow of Earth. This improves the spin-independent cross section
constraints by many orders of magnitude, and closes the window between
astrophysical constraints (at very large cross sections) and underground
detector constraints (at small cross sections). In the applicable mass range,
from about 1 to about 10^{10} GeV, the scattering cross section of dark matter
with nucleons is then bounded from above by the latter constraints, and hence
must be truly weak, as usually assumed.
|
arxiv topic:astro-ph hep-ph nucl-th
|
arxiv_dataset-84705.4398
|
The Dark Side of a Patchwork Universe
gr-qc astro-ph hep-th
While observational cosmology has recently progressed fast, it revealed a
serious dilemma called dark energy: an unknown source of exotic energy with
negative pressure driving a current accelerating phase of the universe. All
attempts so far to find a convincing theoretical explanation have failed, so
that one of the last hopes is the yet to be developed quantum theory of
gravity. In this article, loop quantum gravity is considered as a candidate,
with an emphasis on properties which might play a role for the dark energy
problem. Its basic feature is the discrete structure of space, often associated
with quantum theories of gravity on general grounds. This gives rise to
well-defined matter Hamiltonian operators and thus sheds light on conceptual
questions related to the cosmological constant problem. It also implies typical
quantum geometry effects which, from a more phenomenological point of view, may
result in dark energy. In particular the latter scenario allows several
non-trivial tests which can be made more precise by detailed observations in
combination with a quantitative study of numerical quantum gravity. If the
speculative possibility of a loop quantum gravitational origin of dark energy
turns out to be realized, a program as outlined here will help to hammer out
our ideas for a quantum theory of gravity, and at the same time allow
predictions for the distant future of our universe.
|
arxiv topic:gr-qc astro-ph hep-th
|
arxiv_dataset-85705.4498
|
Atomic Representations of Rank 2 Graph Algebras
math.OA
We provide a detailed analysis of atomic *-representations of rank 2 graphs
on a single vertex. They are completely classified up to unitary equivalence,
and decomposed into a direct sum or direct integral of irreducible atomic
representations. The building blocks are described as the minimal *-dilations
of defect free representations modelled on finite groups of rank 2.
|
arxiv topic:math.OA
|
arxiv_dataset-86705.4598
|
Bs Physics at CDF and D0
hep-ex
Run II at the Tevatron has seen an explosion of results related to the Bs
meson, ranging from tests of QCD models, to probes of electro-weak symmetry
breaking, to direct searches for new physics effects. I will briefly summarize
the CDF and D0 Bs-physics programs, describing the suitability of the detectors
for doing this kind of physics, and pointing out how our knowledge of important
quantities has improved through Run II measurements.
|
arxiv topic:hep-ex
|
arxiv_dataset-87706.0014
|
Towards an exact adaptive algorithm for the determinant of a rational
matrix
cs.SC
In this paper we propose several strategies for the exact computation of the
determinant of a rational matrix. First, we use the Chinese Remaindering
Theorem and the rational reconstruction to recover the rational determinant
from its modular images. Then we show a preconditioning for the determinant
which allows us to skip the rational reconstruction process and reconstruct an
integer result. We compare those approaches with matrix preconditioning which
allow us to treat integer instead of rational matrices. This allows us to
introduce integer determinant algorithms to the rational determinant problem.
In particular, we discuss the applicability of the adaptive determinant
algorithm of [9] and compare it with the integer Chinese Remaindering scheme.
We present an analysis of the complexity of the strategies and evaluate their
experimental performance on numerous examples. This experience allows us to
develop an adaptive strategy which would choose the best solution at the run
time, depending on matrix properties. All strategies have been implemented in
LinBox linear algebra library.
|
arxiv topic:cs.SC
|
arxiv_dataset-88706.0114
|
A New Template Family For The Detection Of Gravitational Waves From
Comparable Mass Black Hole Binaries
gr-qc
In order to improve the phasing of the comparable-mass waveform as we
approach the last stable orbit for a system, various re-summation methods have
been used to improve the standard post-Newtonian waveforms. In this work we
present a new family of templates for the detection of gravitational waves from
the inspiral of two comparable-mass black hole binaries. These new adiabatic
templates are based on re-expressing the derivative of the binding energy and
the gravitational wave flux functions in terms of shifted Chebyshev
polynomials. The Chebyshev polynomials are a useful tool in numerical methods
as they display the fastest convergence of any of the orthogonal polynomials.
In this case they are also particularly useful as they eliminate one of the
features that plagues the post-Newtonian expansion. The Chebyshev binding
energy now has information at all post-Newtonian orders, compared to the
post-Newtonian templates which only have information at full integer orders. In
this work, we compare both the post-Newtonian and Chebyshev templates against a
fiducially exact waveform. This waveform is constructed from a hybrid method of
using the test-mass results combined with the mass dependent parts of the
post-Newtonian expansions for the binding energy and flux functions. Our
results show that the Chebyshev templates achieve extremely high fitting
factors at all PN orders and provide excellent parameter extraction. We also
show that this new template family has a faster Cauchy convergence, gives a
better prediction of the position of the Last Stable Orbit and in general
recovers higher Signal-to-Noise ratios than the post-Newtonian templates.
|
arxiv topic:gr-qc
|
arxiv_dataset-89706.0214
|
Visualizing pair formation on the atomic scale in the high-Tc
superconductor Bi2Sr2CaCu2O8+d
cond-mat.supr-con cond-mat.str-el
Pairing of electrons in conventional superconductors occurs at the
superconducting transition temperature Tc, creating an energy gap D in the
electronic density of states (DOS). In the high-Tc superconductors, a partial
gap in the DOS exists for a range of temperatures above Tc. A key question is
whether the gap in the DOS above Tc is associated with pairing, and what
determines the temperature at which incoherent pairs form. Here we report the
first spatially resolved measurements of gap formation in a high-Tc
superconductor, measured on Bi2Sr2CaCu2O8+d samples with different Tc values
(hole concentration of 0.12 to 0.22) using scanning tunnelling microscopy. Over
a wide range of doping from 0.16 to 0.22 we find that pairing gaps nucleate in
nanoscale regions above Tc. These regions proliferate as the temperature is
lowered, resulting in a spatial distribution of gap sizes in the
superconducting state. Despite the inhomogeneity, we find that every pairing
gap develops locally at a temperature Tp, following the relation 2D/kBTp = 8.
At very low doping (<0.14), systematic changes in the DOS indicate the presence
of another phenomenon, which is unrelated and perhaps competes with electron
pairing. Our observation of nanometre-sized pairing regions provides the
missing microscopic basis for understanding recent reports of fluctuating
superconducting response above Tc in hole-doped high-Tc copper oxide
superconductors.
|
arxiv topic:cond-mat.supr-con cond-mat.str-el
|
arxiv_dataset-90706.0314
|
Lagrangian Approach to Dispersionless KdV Hierarchy
nlin.SI
We derive a Lagrangian based approach to study the compatible Hamiltonian
structure of the dispersionless KdV and supersymmetric KdV hierarchies and
claim that our treatment of the problem serves as a very useful supplement of
the so-called r-matrix method. We suggest specific ways to construct results
for conserved densities and Hamiltonian operators. The Lagrangian formulation,
via Noether's theorem, provides a method to make the relation between
symmetries and conserved quantities more precise. We have exploited this fact
to study the variational symmetries of the dispersionless KdV equation.
|
arxiv topic:nlin.SI
|
arxiv_dataset-91706.0414
|
Engineered quantum tunnelling in extended periodic potentials
cond-mat.other
Quantum tunnelling from a tilted, but otherwise periodic potential is
studied. Our theoretical and experimental results show that, by controlling the
system's parameters, we can engineer the escape rate of a Bose-Einstein
condensate to an exceptional degree. Possible applications of this atom-optics
realization of the open Wannier-Stark system are discussed.
|
arxiv topic:cond-mat.other
|
arxiv_dataset-92706.0514
|
Runaway in the Landscape
hep-th
We consider flux compactifications of type IIB string theory on the mirror of
a rigid Calabi-Yau. In special cases, these models are dual to the type IIA
flux vacua with runaway direction in flux space. We show that new weak coupling
AdS solutions can be found for large complex structure, while Minkowski
solutions with all moduli stabilized are confined to be at strong coupling. The
existence of these solutions, as found in a previous work, is nevertheless
guaranteed by a non-renormalization theorem of the type IIB flux
superpotential. Based on our results, we are led to the conjecture that
supersymmetric runaway directions in flux space are always accompanied by a
spectrum of moduli masses reaching down to the AdS scale. This could be
violated in a non-supersymmetric situation.
|
arxiv topic:hep-th
|
arxiv_dataset-93706.0614
|
An expansion for self-interacting random walks
math.PR math-ph math.MP
We derive a perturbation expansion for general self-interacting random walks,
where steps are made on the basis of the history of the path. Examples of
models where this expansion applies are reinforced random walk, excited random
walk, the true (weakly) self-avoiding walk, loop-erased random walk, and
annealed random walk in random environment.
In this paper we show that the expansion gives rise to useful formulae for
the speed and variance of the random walk, when these quantities are known to
exist. The results and formulae of this paper have been used elsewhere by the
authors to prove monotonicity properties for the speed (in high dimensions) of
excited random walk and related models, and certain models of random walk in
random environment.
We also derive a law of large numbers and central limit theorem (with
explicit error terms) directly from this expansion, under strong assumptions on
the expansion coefficients. The assumptions are shown to be satisfied by
excited random walk in high dimensions with small excitation parameter, a model
of reinforced random walk with underlying drift and small reinforcement
parameter, and certain models of random walk in random environment under strong
ellipticity conditions. This is the extended version of the paper, where we
provide all proofs.
|
arxiv topic:math.PR math-ph math.MP
|
arxiv_dataset-94706.0714
|
The born again (VLTP) scenario revisited: The mass of the remnants and
implications for V4334 Sgr
astro-ph
We present 1-D numerical simulations of the very late thermal pulse
(VLTP) scenario for a wide range of remnant masses. We show that by taking
into account the different possible remnant masses, the observed evolution of
V4334 Sgr (a.k.a. Sakurai's Object) can be reproduced within the standard
1D-MLT stellar evolutionary models without the inclusion of any $ad-hoc$
reduced mixing efficiency. Our simulations hint at a consistent picture with
present observations of V4334 Sgr. From energetics, and within the standard MLT
approach, we show that low mass remnants \hbox{($M\lesssim0.6$\msun)} are
expected to behave markedly different than higher mass remnants
\hbox{($M\gtrsim0.6$\msun)} in the sense that the latter are not expected to
expand significantly as a result of the violent H-burning that takes place
during the VLTP. We also assess the discrepancy in the born again times
obtained by different authors by comparing the energy that can be liberated by
H-burning during the VLTP event.
|
arxiv topic:astro-ph
|
arxiv_dataset-95706.0814
|
New conditional symmetries and exact solutions of nonlinear
reaction-diffusion-convection equations. II
math-ph math.MP
In the first part of this paper math-ph/0612078, a complete description of
Q-conditional symmetries for two classes of reaction-diffusion-convection
equations with power diffusivities is derived. It was shown that all the known
results for reaction-diffusion equations with power diffusivities follow as
particular cases from those obtained in math-ph/0612078 but not vise versa. In
the second part the symmetries obtained in are successfully applied for
constructing exact solutions of the relevant equations. In the particular case,
new exact solutions of nonlinear reaction-diffusion-convection (RDC) equations
arising in application and their natural generalizations are found.
|
arxiv topic:math-ph math.MP
|
arxiv_dataset-96706.0914
|
Four quasars above redshift 6 discovered by the Canada-France High-z
Quasar Survey
astro-ph
The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed
to locate quasars during the epoch of reionization. In this paper we present
the discovery of the first four CFHQS quasars at redshift greater than 6,
including the most distant known quasar, CFHQS J2329-0301 at z=6.43. We
describe the observational method used to identify the quasars and present
optical, infrared, and millimeter photometry and optical and near-infrared
spectroscopy. We investigate the dust properties of these quasars finding an
unusual dust extinction curve for one quasar and a high far-infrared luminosity
due to dust emission for another. The mean millimeter continuum flux for CFHQS
quasars is substantially lower than that for SDSS quasars at the same redshift,
likely due to a correlation with quasar UV luminosity. For two quasars with
sufficiently high signal-to-noise optical spectra, we use the spectra to
investigate the ionization state of hydrogen at z>5. For CFHQS J1509-1749 at
z=6.12, we find significant evolution (beyond a simple extrapolation of lower
redshift data) in the Gunn-Peterson optical depth at z>5.4. The line-of-sight
to this quasar has one of the highest known optical depths at z~5.8. An
analysis of the sizes of the highly-ionized near-zones in the spectra of two
quasars at z=6.12 and z=6.43 suggest the IGM surrounding these quasars was
substantially ionized before these quasars turned on. Together, these
observations point towards an extended reionization process, but we caution
that cosmic variance is still a major limitation in z>6 quasar observations.
|
arxiv topic:astro-ph
|
arxiv_dataset-97706.1014
|
Scattering of Topological Solitons on Barriers and Holes in Two \lambda
\phi^4 Models
hep-th
We present results of our studies of various scattering properties of
topological solitons on obstructions in the form of holes and barriers in 1+1
dimensions. Our results are based on two models involving a \phi^4 potential.
The obstructions are characterised by a potential parameter, \lambda which has
a non-zero value in a certain region of space and zero elsewhere. In the first
model the potential parameter is included in the potential and in the second
model the potential parameter is included in the metric. Our results are based
on numerical simulations and analytical considerations.
|
arxiv topic:hep-th
|
arxiv_dataset-98706.1114
|
Peculiarities of the hidden nonlinear supersymmetry of Poschl-Teller
system in the light of Lame equation
hep-th math-ph math.MP nlin.SI quant-ph
A hidden nonlinear bosonized supersymmetry was revealed recently in
Poschl-Teller and finite-gap Lame systems. In spite of the intimate
relationship between the two quantum models, the hidden supersymmetry in them
displays essential differences. In particular, the kernel of the supercharges
of the Poschl-Teller system, unlike the case of Lame equation, includes
nonphysical states. By means of Lame equation, we clarify the nature of these
peculiar states, and show that they encode essential information not only on
the original hyperbolic Poschl-Teller system, but also on its singular
hyperbolic and trigonometric modifications, and reflect the intimate relation
of the model to a free particle system.
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arxiv topic:hep-th math-ph math.MP nlin.SI quant-ph
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arxiv_dataset-99706.1214
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A High-Resolution Survey of Low-Redshift QSO Absorption Lines:
Statistics and Physical Conditions of O VI Absorbers
astro-ph
Using high-resolution UV spectra of 16 low-z QSOs, we study the physical
conditions and statistics of O VI absorption in the IGM at z < 0.5. We identify
51 intervening (z_{abs} << z_{QSO}) O VI systems comprised of 77 individual
components, and we find 14 "proximate" systems (z_{abs} ~ z_{QSO}) containing
34 components. For intervening systems [components] with rest-frame equivalent
width W_{r} > 30 mA, the number of O VI absorbers per unit redshift dN/dz =
15.6(+2.9/-2.4) [21.0(+3.2/-2.8)], and this decreases to dN/dz = 0.9(+1.0/-0.5)
[0.3(+0.7/-0.3)] for W_{r} > 300 mA. The number per redshift increases steeply
as z_{abs} approaches z_{QSO}, and some proximate absorbers have substantially
lower H I/O VI ratios. The lower proximate ratios could be partially due to
ionization effects but also require higher metallicities. We find that 37% of
the intervening O VI absorbers have velocity centroids that are well-aligned
with corresponding H I absorption. If the O VI and the H I trace the same gas,
the relatively small differences in line widths imply the absorbers are cool
with T < 10^{5} K. Most of these well-aligned absorbers have the
characteristics of metal-enriched photoionized gas. However, the O VI in the
apparently simple and cold systems could be associated with a hot phase with T
~ 10^{5.5} K if the metallicity is high enough to cause the associated broad Ly
alpha absorption to be too weak to detect. We show that 53% of the intervening
O VI systems are complex multiphase absorbers that can accommodate both lower
metallicity collisionally-ionized gas with T > 10^{5} K and cold photoionzed
gas.
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arxiv topic:astro-ph
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