912 research outputs found
Spatial variations of the fine-structure constant in symmetron models
We investigate the variation of the fine-structure constant, {\alpha}, in
symmetron models using N-body simulations in which the full spatial
distribution of {\alpha} at different redshifts has been calculated. In
particular, we obtain simulated sky maps for this variation, and determine its
power spectrum. We find that in high-density regions of space (such as deep
inside dark matter halos) the value of {\alpha} approaches the value measured
on Earth. In the low-density outskirts of halos the scalar field value can
approach the symmetry breaking value and leads to significantly different
values of {\alpha}. If the scalar-photon coupling strength {\beta}{\gamma} is
of order unity we find that the variation of {\alpha} inside dark matter halos
can be of the same magnitude as the recent claims by Webb et al. of a dipole
variation. Importantly, our results also show that with low-redshift symmetry
breaking these models exhibit some dependence of {\alpha} on lookback time (as
opposed to a pure spatial dipole) which could in principle be detected by
sufficiently accurate spectroscopic measurements, such as those of ALMA and the
ELT-HIRES.Comment: 11 pages, 9 figure
Chameleons with Field Dependent Couplings
Certain scalar-tensor theories exhibit the so-called chameleon mechanism,
whereby observational signatures of scalar fields are hidden by a combination
of self-interactions and interactions with ambient matter. Not all
scalar-tensor theories exhibit such a chameleon mechanism, which has been
originally found in models with inverse power run-away potentials and field
independent couplings to matter. In this paper we investigate field-theories
with field-dependent couplings and a power-law potential for the scalar field.
We show that the theory indeed is a chameleon field theory. We find the
thin-shell solution for a spherical body and investigate the consequences for
E\"ot-Wash experiments, fifth-force searches and Casimir force experiments.
Requiring that the scalar-field evades gravitational tests, we find that the
coupling is sensitive to a mass-scale which is of order of the Hubble scale
today.Comment: 17 pages, 20 figure
Nonlinear Enhancement of the Multiphonon Coulomb Excitation in Relativistic Heavy Ion Collisions
We propose a soluble model to incorporate the nonlinear effects in the
transition probabilities of the multiphonon Giant Dipole Resonances based on
the SU(1,1) algebra. Analytical expressions for the multi-phonon transition
probabilities are derived. Enhancement of the Double Giant Resonance excitation
probabilities in relativistic ion collisions scales as for
the degree of nonlinearity and is able to reach values
compatible with experimental data. The enhancement factor is found to decrease
with increasing bombarding energy. [KEYWORDS: Relativistic Heavy Ion
Collisions,Double Giant Resonance]Comment: 12 pages, 2 figure
Intermediate energy Coulomb excitation as a probe of nuclear structure at radioactive beam facilities
The effects of retardation in the Coulomb excitation of radioactive nuclei in
intermediate energy collisions (Elab ~100 MeV/nucleon) are investigated. We
show that the excitation cross sections of low-lying states in 11Be,
{38,40,42}S and {44,46}Ar projectiles incident on gold and lead targets are
modified by as much as 20% due to these effects. The angular distributions of
decaying gamma-rays are also appreciably modified.Comment: 21 pages, 3 figures, Phys. Rev. C, in pres
Breakup of F on Pb near the Coulomb barrier
Angular distributions of oxygen produced in the breakup of F incident
on a Pb target have been measured around the grazing angle at beam
energies of 98 and 120 MeV. The data are dominated by the proton stripping
mechanism and are well reproduced by dynamical calculations. The measured
breakup cross section is approximately a factor of 3 less than that of fusion
at 98 MeV. The influence of breakup on fusion is discussed.Comment: 7 pages, 8 figure
Theory of Multiphonon Excitation in Heavy-Ion Collisions
We study the effects of channel coupling in the excitation dynamics of giant
resonances in relativistic heavy ions collisions. For this purpose, we use a
semiclassical approximation to the Coupled-Channels problem and separate the
Coulomb and the nuclear parts of the coupling into their main multipole
components. In order to assess the importance of multi-step processes, we
neglect the resonance widths and solve the set of coupled equations exactly.
Finite widths are then considered. In this case, we handle the coupling of the
ground state with the dominant Giant Dipole Resonance exactly and study the
excitation of the remaining resonances within the Coupled-Channels Born
Approximation. A comparison with recent experimental data is made.Comment: 29 pages, 7 Postscript figures available upon reques
Meta-Analysis of in vitro-Differentiated Macrophages Identifies Transcriptomic Signatures That Classify Disease Macrophages in vivo
Macrophages are heterogeneous leukocytes regulated in a tissue- and disease-specific context. While in vitro macrophage models have been used to study diseases empirically, a systematic analysis of the transcriptome thereof is lacking. Here, we acquired gene expression data from eight commonly-used in vitro macrophage models to perform a meta-analysis. Specifically, we obtained gene expression data from unstimulated macrophages (M0) and macrophages stimulated with lipopolysaccharides (LPS) for 2-4 h (M-LPSearly), LPS for 24 h (M-LPSlate), LPS and interferon-gamma (M-LPS+IFN gamma), IFN gamma (M-IFN gamma), interleukin-4 (M-IL4), interleukin-10 (M-IL10), and dexamethasone (M-dex). Our meta-analysis identified consistently differentially expressed genes that have been implicated in inflammatory and metabolic processes. In addition, we built macIDR, a robust classifier capable of distinguishing macrophage activation states with high accuracy (>0.95). We classified in vivo macrophages with macIDR to define their tissue- and disease-specific characteristics. We demonstrate that alveolar macrophages display high resemblance to IL10 activation, but show a drop in IFN gamma signature in chronic obstructive pulmonary disease patients. Adipose tissue-derived macrophages were classified as unstimulated macrophages, but acquired LPS-activation features in diabetic-obese patients. Rheumatoid arthritis synovial macrophages exhibit characteristics of IL10- or IFN gamma-stimulation. Altogether, we defined consensus transcriptional profiles for the eight in vitro macrophage activation states, built a classification model, and demonstrated the utility of the latter for in vivo macrophages
Particle emission following Coulomb excitation in ultrarelativistic heavy-ion collisions
We study nuclear reactions induced by virtual photons associated with
Lorentz-boosted Coulomb fields of ultrarelativistic heavy ions. Evaporation,
fission and multifragmentation mechanisms are included in a new RELDIS code,
which describes the deexcitation of residual nuclei formed after single and
double photon absorption in peripheral heavy-ion collisions. Partial cross
sections for different dissociation channels, including the multiple neutron
emission ones, are calculated and compared with data when available. Rapidity
and transverse momentum distributions of nucleons, nuclear fragments and pions,
produced electromagnetically, are also calculated. These results provide
important information for designing large-rapidity detectors and zero-degree
calorimeters at RHIC and LHC. The electromagnetic dissociation of nuclei
imposes some constrains on the investigation of exotic particle production in
gamma-gamma fusion reactions.Comment: 26 LaTeX pages including 8 figures, uses epsf.st
Region of hadron-quark mixed phase in hybrid stars
Hadron--quark mixed phase is expected in a wide region of the inner structure
of hybrid stars. However, we show that the hadron--quark mixed phase should be
restricted to a narrower region to because of the charge screening effect. The
narrow region of the mixed phase seems to explain physical phenomena of neutron
stars such as the strong magnetic field and glitch phenomena, and it would give
a new cooling curve for the neutron star.Comment: to be published in Physical Review
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