224,025 research outputs found
Electromagnetic Meson Form Factors in the Salpeter Model
We present a covariant scheme to calculate mesonic transitions in the
framework of the Salpeter equation for -states. The full Bethe
Salpeter amplitudes are reconstructed from equal time amplitudes which were
obtained in a previous paper\cite{Mue} by solving the Salpeter equation for a
confining plus an instanton induced interaction. This method is applied to
calculate electromagnetic form factors and decay widths of low lying
pseudoscalar and vector mesons including predictions for CEBAF experiments. We
also describe the momentum transfer dependence for the processes
.Comment: 22 pages including 10 figure
Level-crossing spectroscopy of the 7, 9, and 10D_5/2 states of 133Cs and validation of relativistic many-body calculations of the polarizabilities and hyperfine constants
We present an experimental and theoretical investigation of the
polarizabilities and hyperfine constants of D_J states in 133Cs for J=3/2 and
J=5/2. New experimental values for the hyperfine constant A are obtained from
level-crossing signals of the (7,9,10)D_5/2 states of 133Cs and precise
calculations of the tensor polarizabilities alpha_2. The results of
relativistic many-body calculations for scalar and tensor polarizabilities of
the (5-10)D_3/2 and (5-10)D_5/2 states are presented and compared with measured
values from the literature. Calculated values of the hyperfine constants A for
these states are also presented and checked for consistency with experimental
values.Comment: 12 pages, revtex4, 11 figure file
Neutrino mass, proton decay and dark matter in TeV scale universal extra dimension models
We show how the problem of small neutrino masses and suppressed proton decay
can be simultaneously resolved in 6-D universal extra dimension models (UED)
with a low fundamental scale using extended gauge groups that contain the local
symmetry. The extra space dimensions are compactified either on a
or orbifold depending on whether the full gauge
group is or . In both cases, neutrino masses are suppressed by
an appropriate orbifold parity assignment for the standard model singlet
neutrinos and the proton decay rate is suppressed due to a residual discrete
symmetry left over from compactification. For lower values of the fundamental
scale, a dominant decay mode of the neutron is . An interesting
consequence of the model is a possible two component picture for dark matter of
the universe.Comment: 25 pages, two minor typos correcte
Solitons on the edge of a two-dimensional electron system
We present a study of the excitations of the edge of a two-dimensional
electron droplet in a magnetic field in terms of a contour dynamics formalism.
We find that, beyond the usual linear approximation, the non-linear analysis
yields soliton solutions which correspond to uniformly rotating shapes. These
modes are found from a perturbative treatment of a non-linear eigenvalue
problem, and as solutions to a modified Korteweg-de Vries equation resulting
from a local induction approximation to the nonlocal contour dynamics. We
discuss applications to the edge modes in the quantum Hall effect.Comment: 4 pages, 2 eps figures (included); to appear in Phys. Rev. Letter
Hierarchies without Symmetries from Extra Dimensions
It is commonly thought that small couplings in a low-energy theory, such as
those needed for the fermion mass hierarchy or proton stability, must originate
from symmetries in a high-energy theory. We show that this expectation is
violated in theories where the Standard Model fields are confined to a thick
wall in extra dimensions, with the fermions "stuck" at different points in the
wall. Couplings between them are then suppressed due to the exponentially small
overlaps of their wave functions. This provides a framework for understanding
both the fermion mass hierarchy and proton stability without imposing
symmetries, but rather in terms of higher dimensional geography. A model
independent prediction of this scenario is non-universal couplings of the
Standard Model fermions to the ``Kaluza-Klein'' excitations of the gauge
fields. This allows a measurement of the fermion locations in the extra
dimensions at the LHC or NLC if the wall thickness is close to the TeV scale.Comment: 25 pages, 7 figure
Fractional Generalization of Gradient Systems
We consider a fractional generalization of gradient systems. We use
differential forms and exterior derivatives of fractional orders. Examples of
fractional gradient systems are considered. We describe the stationary states
of these systems.Comment: 11 pages, LaTe
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Small, Low-energy, Dispersive Solar Energetic Particle Events Observed by Parker Solar Probe
The Energetic Particle InstrumentâLow Energy (EPI-Lo) experiment has detected several weak, low-energy (~30â300 keV nucleonâ»Âč) solar energetic particle (SEP) events during its first two closest approaches to the Sun, providing a unique opportunity to explore the sources of low-energy particle acceleration. As part of the Parker Solar Probe (PSP) Integrated Science Investigation of the Sun (ISâIS) suite, EPI-Lo was designed to investigate the physics of energetic particles; however, in the special lowest-energy "time-of-flight only" product used in this study, it also responds to solar photons in a subset of approximately sunward-looking apertures lacking special light-attenuating foils. During the first three perihelia, in a frame rotating with the Sun, PSP undergoes retrograde motion, covering a 17° heliographic longitudinal range three times during the course of the ~11-day perihelion passes, permitting a unique spatial and temporal study into the location, correlation, and persistence of previously unmeasurable SEPs. We examine the signatures of these SEPs (during the first PSP perihelion pass only) and the connection to possible solar sources using remote observations from the Solar Dynamics Observatory (SDO), the Solar TErrestrial RElations Observatory (STEREO), and the ground-based Global Oscillation Network Group (GONG). The orientation of the Sun relative to STEREO, SDO, and GONG makes such identifications challenging, but we do have several candidates, including an equatorial coronal hole at a Carrington longitude of ~335°. To analyze observations from EPI-Lo, which is a new type of particle instrument, we examine instrumental effects and provide a preliminary separation of the ion signal from the photon background
Complex X-ray Absorption and the Fe Kalpha Profile in NGC 3516
We present data from simultaneous Chandra, XMM-Newton and BeppoSAX
observations of the Seyfert 1 galaxy NGC 3516, taken during 2001 April and Nov.
We have investigated the nature of the very flat observed X-ray spectrum.
Chandra grating data show the presence of X-ray absorption lines, revealing two
distinct components of the absorbing gas, one which is consistent with our
previous model of the UV/X-ray absorber while the other, which is outflowing at
a velocity of ~1100 km/s has a larger column density and is much more highly
ionized. The broad-band spectral characteristics of the X-ray continuum
observed with XMM during 2001 April, reveal the presence of a third layer of
absorption consisting of a very large column (~2.5 x 10E23 cm^-2) of highly
ionized gas with a covering fraction ~50%. This low covering fraction suggests
that the absorber lies within a few lt-days of the X-ray source and/or is
filamentary in structure. Interestingly, these absorbers are not in thermal
equilibrium with one another. The two new components are too highly ionized to
be radiatively accelerated, which we suggest is evidence for a hydromagnetic
origin for the outflow. Applying our model to the Nov dataset, we can account
for the spectral variability primarily by a drop in the ionization states of
the absorbers, as expected by the change in the continuum flux. When this
complex absorption is accounted for we find the underlying continuum to be
typical of Seyfert 1 galaxies. The spectral curvature attributed to the high
column absorber, in turn, reduces estimates of the flux and extent of any broad
Fe emission line from the accretion disk.Comment: 33 pages, 9 figures, accepted for publication in Ap
Dynamical Casimir Effect with Semi-Transparent Mirrors, and Cosmology
After reviewing some essential features of the Casimir effect and,
specifically, of its regularization by zeta function and Hadamard methods, we
consider the dynamical Casimir effect (or Fulling-Davis theory), where related
regularization problems appear, with a view to an experimental verification of
this theory. We finish with a discussion of the possible contribution of vacuum
fluctuations to dark energy, in a Casimir like fashion, that might involve the
dynamical version.Comment: 11 pages, Talk given in the Workshop ``Quantum Field Theory under the
Influence of External Conditions (QFEXT07)'', Leipzig (Germany), September 17
- 21, 200
Thermal Background Corrections to the Neutrino Electromagnetic Vertex in Models with Charged Scalar Bosons
We calculate the correction to the neutrino electromagnetic vertex due to
background of electrons in a large class of models, as the supersymmetric model
with explicit breaking of R-parity, where charged scalar bosons couple to
leptons and which are able to provide an astrophysically interesting value for
the neutrino magnetic (electric) moment, . We show
that the medium contribution to the chirality flipping magnetic (electric)
dipole moment is not significant, however a new chirality flipping, but
helicity conserving, term arises. It signals the presence of and
asymmetries in the medium and is associated to the longitudinal
photon and therefore disappears in the vacuum. We estimate the contribution of
this new term to the rate of the plasmon decay process in the core of degenerate stars, showing that it can be comparable with
the contribution coming from the vacuum magnetic (dipole) moment. We also
calculate the correction to the effective potential of a propagating neutrino
in presence of a magnetic field due to a chirality preserving contribution to
the diagonal magnetic moment from the medium. This contribution is identical
for particles and antiparticles and so need not to vanish for Majorana
neutrinos.Comment: DFPD 93/TH/75, SISSA 93/183/A preprint, 25 pages + 4 figures
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