32,889 research outputs found
The ping-pong protocol can be attacked without eavesdropping
Attack the ping-pong protocol without eavesdropping.Comment: PACS: 03.67.H
Phase-reference VLBI Observations of the Compact Steep-Spectrum Source 3C 138
We investigate a phase-reference VLBI observation that was conducted at 15.4
GHz by fast switching VLBA antennas between the compact steep-spectrum radio
source 3C 138 and the quasar PKS 0528+134 which are about 4 away on the
sky. By comparing the phase-reference mapping with the conventional hybrid
mapping, we demonstrate the feasibility of high precision astrometric
measurements for sources separated by 4. VLBI phase-reference mapping
preserves the relative phase information, and thus provides an accurate
relative position between 3C 138 and PKS 0528+134 of
and
(J2000.0) in right ascension and declination, respectively. This gives an
improved position of the nucleus (component A) of 3C 138 in J2000.0 to be
RA= and Dec= under the
assumption that the position of calibrator PKS 0528+134 is correct. We further
made a hybrid map by performing several iterations of CLEAN and
self-calibration on the phase-referenced data with the phase-reference map as
an input model for the first phase self-calibration. Compared with the hybrid
map from the limited visibility data directly obtained from fringe fitting 3C
138 data, this map has a similar dynamic range, but a higher angular
resolution. Therefore, phase-reference technique is not only a means of phase
connection, but also a means of increasing phase coherence time allowing
self-calibration technique to be applied to much weaker sources.Comment: 9 pages plus 2 figures, accepted by PASJ (Vol.58 No.6
What can we learn from decays?
We investigate the decays under the
factorization scheme and find many discrepancies between theoretical
predictions and the experimental data. In the tree dominated processes, large
contributions from color-suppressed tree diagrams are required in order to
accommodate with the large decay rates of and . For decays which are both induced
by transition, theoretical predictions on their decay rates are larger
than the data by a factor of 2.8 and 5.5, respectively. Large electro-weak
penguins or some new mechanism are expected to explain the branching ratios of
and . The
soft-collinear-effective-theory has the potential to explain large decay rates
of and via a large hard-scattering form
factor . We will also show that, with proper charming
penguins, predictions on the branching ratios of can also be consistent with the data.Comment: 16 pages, no figur
Dynamic entanglement in oscillating molecules and potential biological implications
We demonstrate that entanglement can persistently recur in an oscillating
two-spin molecule that is coupled to a hot and noisy environment, in which no
static entanglement can survive. The system represents a non-equilibrium
quantum system which, driven through the oscillatory motion, is prevented from
reaching its (separable) thermal equilibrium state. Environmental noise,
together with the driven motion, plays a constructive role by periodically
resetting the system, even though it will destroy entanglement as usual. As a
building block, the present simple mechanism supports the perspective that
entanglement can exist also in systems which are exposed to a hot environment
and to high levels of de-coherence, which we expect e.g. for biological
systems. Our results furthermore suggest that entanglement plays a role in the
heat exchange between molecular machines and environment. Experimental
simulation of our model with trapped ions is within reach of the current
state-of-the-art quantum technologies.Comment: Extended version, including supplementary information. 9 pages, 8
figure
Nonorthogonal decoy-state Quantum Key Distribution
In practical quantum key distribution (QKD), weak coherent states as the
photon sources have a limit in secure key rate and transmission distance
because of the existence of multiphoton pulses and heavy loss in transmission
line. Decoy states method and nonorthogonal encoding protocol are two important
weapons to combat these effects. Here, we combine these two methods and propose
a efficient method that can substantially improve the performance of QKD. We
find a 79 km increase in transmission distance over the prior record using
decoy states method.Comment: 4 pages, 1 figure; Revtex4, submitted to PR
Charmless Two-body decays In Soft-Collinear-Effective-Theory
We provide the analysis of charmless two-body decays under the
framework of the soft-collinear-effective-theory (SCET), where denotes a
light vector (pseudoscalar) meson. Besides the leading power contributions,
some power corrections (chiraly enhanced penguins) are also taken into account.
Using the current available and experimental data on
branching fractions and CP asymmetry variables, we find two kinds of solutions
in fit for the 16 non-perturbative inputs which are essential in the
87 and decay channels. Chiraly enhanced penguins can change
several charming penguins sizably, since they share the same topology. However,
most of the other non-perturbative inputs and predictions on branching ratios
and CP asymmetries are not changed too much. With the two sets of inputs, we
predict the branching fractions and CP asymmetries of other modes especially
decays. The agreements and differences with results in QCD
factorization and perturbative QCD approach are analyzed. We also study the
time-dependent CP asymmetries in channels with CP eigenstates in the final
states and some other channels such as and
. In the perturbative QCD approach, the
penguins in annihilation diagrams play an important role. Although
they have the same topology with charming penguins in SCET, there are many
differences between the two objects in weak phases, magnitudes, strong phases
and factorization properties.Comment: 34 pages, revtex, 2 figures, published at PR
Multi-epoch VLBA observations of 3C 66A
We present the results of six-epoch Very Long Baseline Array (VLBA)
observations of 3C~66A. The high-resolution Very Long Baseline Interferometer
(VLBI) maps obtained at multi-frequency (2.3, 8.4, and 22.2 GHz) simultaneously
enabled us to identify the brightest compact component with the core. We find
that the spectrum of the core can be reasonably fitted by the synchrotron
self-absorption model. Our VLBA maps show that the jet of 3C~66A has two
bendings at about 1.2 and 4 mas from the core. We also give possible
identifications of our jet components with the components in previous VLBA
observations by analysing their proper motions. We find consistent differences
of the position from the core in one component between different frequencies at
six epochs.Comment: 10 pages, 5 figures, received 30 January 2007, accepted 22 March 200
Late acceleration and crossing in induced gravity
We study the cosmological evolution on a brane with induced gravity within a
bulk with arbitrary matter content. We consider a Friedmann-Robertson-Walker
brane, invariantly characterized by a six-dimensional group of isometries. We
derive the effective Friedmann and Raychaudhuri equations. We show that the
Hubble expansion rate on the brane depends on the covariantly defined
integrated mass in the bulk, which determines the energy density of the
generalized dark radiation. The Friedmann equation has two branches,
distinguished by the two possible values of the parameter \ex=\pm 1. The
branch with \ex=1 is characterized by an effective cosmological constant and
accelerated expansion for low energy densities. Another remarkable feature is
that the contribution from the generalized dark radiation appears with a
negative sign. As a result, the presence of the bulk corresponds to an
effective negative energy density on the brane, without violation of the weak
energy condition. The transition from a period of domination of the matter
energy density by non-relativistic brane matter to domination by the
generalized dark radiation corresponds to a crossing of the phantom divide
.Comment: 7 pages, no figures, RevTex 4.0; (v2) new references are added, minor
corrections and expanded discussion; (v3) additional comments at the end of
section III, minor corrections and several new references are added, to match
published version in Phys. Rev.
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