9,025 research outputs found
On the coupling of massless particles to scalar fields
It is investigated if massless particles can couple to scalar fields in a
special relativistic theory with classical particles. The only possible obvious
theory which is invariant under Lorentz transformations and reparametrization
of the affine parameter leads to trivial trajectories (straight lines) for the
massless case, and also the investigation of the massless limit of the massive
theory shows that there is no influence of the scalar field on the limiting
trajectories.
On the other hand, in contrast to this result, it is shown that massive
particles are influenced by the scalar field in this theory even in the
ultra-relativistic limit.Comment: 9 pages, no figures, uses titlepage.sty, LaTeX 2.09 file, submitted
to International Journal of Theoretical Physic
Symmetric Brownian motor
In this paper we present a model of a symmetric Brownian motor (SBM) which
changes the sign of its velocity when the temperature gradient is inverted. The
velocity, external work and efficiency are studied as a function of the
temperatures of the baths and other relevant parameters. The motor shows a
current reversal when another parameter (a phase shift) is varied. Analytical
predictions and results from numerical simulations are performed and agree very
well. Generic properties of this type of motors are discussed.Comment: 8 pages and 10 figure
Distilling entanglement from cascades with partial "Which Path" ambiguity
We develop a framework to calculate the density matrix of a pair of photons
emitted in a decay cascade with partial "which path" ambiguity. We describe an
appropriate entanglement distillation scheme which works also for certain
random cascades. The qualitative features of the distilled entanglement are
presented in a two dimensional "phase diagram". The theory is applied to the
quantum tomography of the decay cascade of a biexciton in a semiconductor
quantum dot. Agreement with experiment is obtained
Photon polarization and Wigner's little group
To discuss one-photon polarization states we find an explicit form of the
Wigner's little group element in the massless case for arbitrary Lorentz
transformation. As is well known, when analyzing the transformation properties
of the physical states, only the value of the phase factor is relevant. We show
that this phase factor depends only on the direction of the momentum
and does not depend on the frequency . Finally, we use
this observation to discuss the transformation properties of the linearly
polarized photons and the corresponding reduced density matrix. We find that
they transform properly under Lorentz group.Comment: Version published in Phys. Rev. A, few typos correcte
Softening of the stiffness of bottlebrush polymers by mutual interaction
We study bottlebrush macromolecules in a good solvent by small-angle neutron
scattering (SANS), static light scattering (SLS), and dynamic light scattering
(DLS). These polymers consist of a linear backbone to which long side chains
are chemically grafted. The backbone contains about 1600 monomer units (weight
average) and every second monomer unit carries side-chains with ca. 60 monomer
units. The SLS- and SANS data extrapolated to infinite dilution lead to the
form factor of the polymer that can be described in terms of a worm-like chain
with a contour length of 380 nm and a persistence length of 17.5 nm. An
analysis of the DLS data confirm these model parameters. The scattering
intensities taken at finite concentration can be modeled using the polymer
reference interaction site model. It reveals a softening of the bottlebrush
polymers caused by their mutual interaction. We demonstrate that the
persistence decreases from 17.5 nm down to 5 nm upon increasing the
concentration from dilute solution to the highest concentration 40.59 g/l under
consideration. The observed softening of the chains is comparable to the
theoretically predicted decrease of the electrostatic persistence length of
linear polyelectrolyte chains at finite concentrations.Comment: 4 pages, 4 figure
A photonic cluster state machine gun
We present a method to convert certain single photon sources into devices
capable of emitting large strings of photonic cluster state in a controlled and
pulsed "on demand" manner. Such sources would greatly reduce the resources
required to achieve linear optical quantum computation. Standard spin errors,
such as dephasing, are shown to affect only 1 or 2 of the emitted photons at a
time. This allows for the use of standard fault tolerance techniques, and shows
that the photonic machine gun can be fired for arbitrarily long times. Using
realistic parameters for current quantum dot sources, we conclude high
entangled-photon emission rates are achievable, with Pauli-error rates per
photon of less than 0.2%. For quantum dot sources the method has the added
advantage of alleviating the problematic issues of obtaining identical photons
from independent, non-identical quantum dots, and of exciton dephasing.Comment: Final version accepted to Physical Review Letters, includes the
supplemtary material with some more detailed calculation
A Universal Action Formula
A universal formula for an action associated with a noncommutative geometry,
defined by a spectal triple (\Ac ,\Hc ,D), is proposed. It is based on the
spectrum of the Dirac operator and is a geometric invariant. The new symmetry
principle is the automorphism of the algebra \Ac which combines both
diffeomorphisms and internal symmetries. Applying this to the geometry defined
by the spectrum of the standard model gives an action that unifies gravity with
the standard model at a very high energy scale.Comment: This is a short non technical letter based on the longer version,
hep-th/9606001. Tex file, 10 page
Pulsation period variations in the RRc Lyrae star KIC 5520878
Learned et. al. proposed that a sufficiently advanced extra-terrestrial
civilization may tickle Cepheid and RR Lyrae variable stars with a neutrino
beam at the right time, thus causing them to trigger early and jogging the
otherwise very regular phase of their expansion and contraction. This would
turn these stars into beacons to transmit information throughout the galaxy and
beyond. The idea is to search for signs of phase modulation (in the regime of
short pulse duration) and patterns, which could be indicative of intentional,
omnidirectional signaling.
We have performed such a search among variable stars using photometric data
from the Kepler space telescope. In the RRc Lyrae star KIC 5520878, we have
found two such regimes of long and short pulse durations. The sequence of
period lengths, expressed as time series data, is strongly auto correlated,
with correlation coefficients of prime numbers being significantly higher
(\%). Our analysis of this candidate star shows that the prime number
oddity originates from two simultaneous pulsation periods and is likely of
natural origin.
Simple physical models elucidate the frequency content and asymmetries of the
KIC 5520878 light curve.
Despite this SETI null result, we encourage testing other archival and future
time-series photometry for signs of modulated stars. This can be done as a
by-product to the standard analysis, and even partly automated.Comment: Accepted for publication in ApJ. 49 pages, 16 figure
Dynamical Gauge Symmetry Breaking in Extension of the Standard Model
We study the extension of the Standard model with a
strong U(1) coupling. We argue that current experiments limit this coupling to
be relatively large. The model is dynamically broken to the Standard model at the scale of a few TeV with all the extra gauge bosons
and the exotic quarks acquiring masses much larger than the scale of
electroweak symmetry breaking. Furthermore we find that the model leads to
large dynamical mass of the top quark and hence also breaks the electroweak
gauge symmetry. It therefore leads to large dynamical effects within the
Standard model and can partially replace the Higgs interactions.Comment: 4 pages, revtex, no figures; revised version predicting realistic
mass spectru
Prospects of accelerator and reactor neutrino oscillation experiments for the coming ten years
We analyze the physics potential of long baseline neutrino oscillation
experiments planned for the coming ten years, where the main focus is the
sensitivity limit to the small mixing angle . The discussed
experiments include the conventional beam experiments MINOS, ICARUS, and OPERA,
which are under construction, the planned superbeam experiments J-PARC to
Super-Kamiokande and NuMI off-axis, as well as new reactor experiments with
near and far detectors, represented by the Double-Chooz project. We perform a
complete numerical simulation including systematics, correlations, and
degeneracies on an equal footing for all experiments using the GLoBES software.
After discussing the improvement of our knowledge on the atmospheric parameters
and by these experiments, we investigate the
potential to determine within the next ten years in detail.
Furthermore, we show that under optimistic assumptions and for
close to the current bound, even the next generation of experiments might
provide some information on the Dirac CP phase and the type of the neutrino
mass hierarchy.Comment: 38 pages, 13 figures, Eqs. (1) and (5) corrected, small corrections
in Figs. 8, 9, and Tab. 4, discussion improved, ref. added, version to appear
in PRD, high resolution figures are available at
http://www.sns.ias.edu/~winter/figs0403068.htm
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