221 research outputs found
Q-stars and charged q-stars
We present the formalism of q-stars with local or global U(1) symmetry. The
equations we formulate are solved numerically and provide the main features of
the soliton star. We study its behavior when the symmetry is local in contrast
to the global case. A general result is that the soliton remains stable and
does not decay into free particles and the electrostatic repulsion preserves it
from gravitational collapse. We also investigate the case of a q-star with
non-minimal energy-momentum tensor and find that the soliton is stable even in
some cases of collapse when the coupling to gravity is absent.Comment: Latex, 19pg, 12 figures. Accepted in Phys. Rev.
Chiral Lagrangians and Quark Condensate in Nuclei
We study the evolution with density of the quark condensate in the nuclear
medium with interacting nucleons and including the short range correlations. We
work with two chiral models, the linear sigma model and the non-linear one. For
the last one we use two versions, one which does not satisfy PCAC, and another
one which does. We show that the quark condensate, as other observables, is
independent on the variant selected. The application to physical pions excludes
the linear sigma model as a credible one. In the non-linear models our
conclusions are: first there is no systematic reaction imposed by chiral
symmetry against symmetry restoration, second, if one keeps only the s-wave
pion-nucleon interaction, the quark condensate evolves essentially linearly
with density, as if the nucleons were non interacting. The main correction
arises from the p-wave pion-nucleon interaction. Last, in the s-wave optical
potential, chiral symmetry tolerates but does not impose two body terms. On the
other hand the effect of correlations linked to the isospin symmetric amplitude
is negligible.Comment: 24 pages, LaTex, 7 PostScript Figures, a couple of misprints
corrected , 2 references added, a few modifications of the main text and
conclusion, to be published in Nucl. Phys.
EYM equations in the presence of q-stars
We study Einstein-Yang-Mills equations in the presence of gravitating
non-topological soliton field configurations, of q-ball type. We produce
numerical solutions, stable with respect to gravitational collapse and to
fission into free particles, and we study the effect of the field strength and
the eigen-frequency to the soliton parameters. We also investigate the
formation of such soliton stars when the spacetime is asymptotically anti de
Sitter.Comment: 11 pages, to appear in Phys. Rev.
Top Radiative Corrections in Non-minimal Standard Models
We derive the one-loop effective action induced by a heavy top in models with
an extended Higgs sector. We use the effective action to analyze the top
corrections to the parameter and to the Higgs-gauge boson couplings. We
show that in models with at tree-level, one does not lose
generally the bound on from the parameter.Comment: 9 pages, phyzzx file, UPR-0603T. (a new reference has been added
High-Intensity and High-Brightness Source of Moderated Positrons Using a Brilliant gamma Beam
Presently large efforts are conducted towards the development of highly
brilliant gamma beams via Compton back scattering of photons from a
high-brilliance electron beam, either on the basis of a normal-conducting
electron linac or a (superconducting) Energy Recovery Linac (ERL). Particularly
ERL's provide an extremely brilliant electron beam, thus enabling to generate
highest-quality gamma beams. A 2.5 MeV gamma beam with an envisaged intensity
of 10^15 s^-1, as ultimately envisaged for an ERL-based gamma-beam facility,
narrow band width (10^-3), and extremely low emittance (10^-4 mm^2 mrad^2)
offers the possibility to produce a high-intensity bright polarized positron
beam. Pair production in a face-on irradiated W converter foil (200 micron
thick, 10 mm long) would lead to the emission of 2 x 10^13 (fast) positrons per
second, which is four orders of magnitude higher compared to strong radioactive
^22Na sources conventionally used in the laboratory.Using a stack of converter
foils and subsequent positron moderation, a high-intensity low-energy beam of
moderated positrons can be produced. Two different source setups are presented:
a high-brightness positron beam with a diameter as low as 0.2 mm, and a
high-intensity beam of 3 x 10^11 moderated positrons per second. Hence,
profiting from an improved moderation efficiency, the envisaged positron
intensity would exceed that of present high-intensity positron sources by a
factor of 100.Comment: 9 pages, 3 figure
Technicolor Theories with Negative S
We show that the pseudo Nambu--Goldstone boson contribution to the
Peskin--Takeuchi electroweak parameter can be negative in a class of
technicolor theories. This negative contribution can be large enough to cancel
the positive techni-hadron contribution, showing that electroweak precision
tests alone cannot be used to rule out technicolor as the mechanism of
electroweak symmetry breaking.Comment: (LBL-32893, UCB-PTH 92/34, 10 pages; we added a discussion of
uncertainties, fine-tuning, and SU(2) asymptotic freedom; the conclusions are
unchanged.
Pion-Nucleon Scattering in a Large-N Sigma Model
We review the large-N_c approach to meson-baryon scattering, including recent
interesting developments. We then study pion-nucleon scattering in a particular
variant of the linear sigma-model, in which the couplings of the sigma and pi
mesons to the nucleon are echoed by couplings to the entire tower of I=J
baryons (including the Delta) as dictated by large-N_c group theory. We sum the
complete set of multi-loop meson-exchange
\pi N --> \pi N and \pi N --> \sigma N Feynman diagrams, to leading order in
1/N_c. The key idea, reviewed in detail, is that large-N_c allows the
approximation of LOOP graphs by TREE graphs, so long as the loops contain at
least one baryon leg; trees, in turn, can be summed by solving classical
equations of motion. We exhibit the resulting partial-wave S-matrix and the
rich nucleon and Delta resonance spectrum of this simple model, comparing not
only to experiment but also to pion-nucleon scattering in the Skyrme model. The
moral is that much of the detailed structure of the meson-baryon S-matrix which
hitherto has been uncovered only with skyrmion methods, can also be described
by models with explicit baryon fields, thanks to the 1/N_c expansion.Comment: This LaTeX file inputs the ReVTeX macropackage; figures accompany i
Hairs on the cosmological horizon
We investigate the possibility of having hairs on the cosmological horizon.
The cosmological horizon shares similar properties of black hole horizons in
the aspect of having hairs on the horizons. For those theories admitting haired
black hole solutions, the nontrivial matter fields may reach and extend beyond
the cosmological horizon. For Q-stars and boson stars, the matter fields cannot
reach the cosmological horizon. The no short hair conjecture keeps valid,
despite the asymptotic behavior (de Sitter or anti-de Sitter) of black hole
solutions. We prove the no scalar hair theorem for anti-de Sitter black holes.
Using the Bekenstein's identity method, we also prove the no scalar hair
theorem for the de Sitter space and de Sitter black holes if the scalar
potential is convex.Comment: Revtex, no figures, 16 page
SO(5) Invariance and Effective Field Theory for High-Tc Superconductors
We set up the effective field theories which describe the SO(5)-invariant
picture of the high-Tc cuprates in various regimes. We use these to get
quantitative conclusions concerning the size of SO(5)-breaking effects. We
consider two applications in detail: (i) the thermodynamic free energy, which
describe the phase diagram and critical behaviour, and (ii) the Lagrangian
governing the interactions of the pseudo-Goldstone bosons with each other and
with the electron quasiparticles deep within the ordered phases. We use these
effective theories to obtain predictions for the critical behaviour near the
possible bicritical point and the pseudo-Goldstone boson dispersion relations,
as well as some preliminary results concerning their contribution to response
functions. We systematically identify which predictions are independent of the
microscopic details of the underlying electron dynamics, and which depend on
more model-dependent assumptions.Comment: 40 pages, plain TeX, companion article for the letter
cond-mat/961107
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International meta-analysis of PTSD genome-wide association studies identifies sex- and ancestry-specific genetic risk loci.
The risk of posttraumatic stress disorder (PTSD) following trauma is heritable, but robust common variants have yet to be identified. In a multi-ethnic cohort including over 30,000 PTSD cases and 170,000 controls we conduct a genome-wide association study of PTSD. We demonstrate SNP-based heritability estimates of 5-20%, varying by sex. Three genome-wide significant loci are identified, 2 in European and 1 in African-ancestry analyses. Analyses stratified by sex implicate 3 additional loci in men. Along with other novel genes and non-coding RNAs, a Parkinson's disease gene involved in dopamine regulation, PARK2, is associated with PTSD. Finally, we demonstrate that polygenic risk for PTSD is significantly predictive of re-experiencing symptoms in the Million Veteran Program dataset, although specific loci did not replicate. These results demonstrate the role of genetic variation in the biology of risk for PTSD and highlight the necessity of conducting sex-stratified analyses and expanding GWAS beyond European ancestry populations
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