175 research outputs found
Romanian 14 GHz ECR Ion Source RECRIS: main features and first operation
RECRIS, the romanian 14 GHz ECR ion source, designed to be used as a facility for atomic physics and material studies with highly charged ion beams, have been recently completed. The general design [1], the main characteristics and the detailed measurements of the radial [2] and axial magnetic fields are presented. A maximum axial magnetic field of 1.4 T and a mirror ratio of up to 4 were obtained. The dependence of the mirror ratio and of the ECR plasma zone volume on the configuration of the axial magnetic system configuration was studied. The first operation of this source is described, showing a good stability
Metal-dielectric structures for high charge state ion production in ECR plasma
Metal-dielectric (MD) structures of pure (99.999%) aluminum foils were previously studied [1, 2] in the National Institute for Physics and Nuclear Engineering (NIPNE), Bucharest, Romania showing high secondary electron emission properties. Consequently, 26 mm diameter disks of such structures (Al-Al2O3) were tested in the ECR ion source of the Institut fuer Kernphysik (IKF) der J. W. Goethe Universitat, Frankfurt/Main, Germany, allowing to demonstrate their ability to significantly increase the ECRIS performances in what concerns the production of high charge state ions [3]. New experiments carried on in Bucharest on a special facility [2] stressed out the possibility to develop high emissive MD structures starting from lower purity (99%) aluminum foils. This result allowed us to make a special cylinder of 1 mm wall thickness electrolytically treated so that only the inner face had a MD structure layer while the external surface remained metallic. Such a cylinder introduced in the plasma chamber of an ECR ion source provides a high rate of secondary electrons that enhance the ECR plasma electron density while its metallic external surface provides a good electric and thermal contact with the plasma chamber. The tests performed with such a MD aluminum cylinder in the IKF 14 GHz ECR ion source, successfully demonstrated the possibility to shift the ECRIS output toward very high charge states (Ar16+) due to the strong secondary electron emission of the MD inner surface of the cylinder
Dynamical Symmetry Breaking in Warped Compactifications
We study dynamical electroweak symmetry breaking in the Randall-Sundrum
scenario. We show that one extra dimension is enough to give the correct
pattern of electroweak symmetry breaking in a simple model with gauge bosons
and the right-handed top quark in the bulk. The top quark mass is also in
agreement with experiment. Furthermore, we propose an extended scenario with
all Standard Model gauge bosons and fermions propagating in the bulk, which
naturally accommodates the fermion mass hierarchies. No new fields or
interactions beyond the observed in the Standard Model are required.Comment: 16 pages, no figures. v3 : Final version, to be published in Phys.
Rev.
Minimal Composite Higgs Model with Light Bosons
We analyze a composite Higgs model with the minimal content that allows a
light Standard-Model-like Higgs boson, potentially just above the current LEP
limit. The Higgs boson is a bound state made up of the top quark and a heavy
vector-like quark. The model predicts that only one other bound state may be
lighter than the electroweak scale, namely a CP-odd neutral scalar. Several
other composite scalars are expected to have masses in the TeV range. If the
Higgs decay into a pair of CP-odd scalars is kinematically open, then this
decay mode is dominant, with important implications for Higgs searches. The
lower bound on the CP-odd scalar mass is loose, in some cases as low as
100 MeV, being set only by astrophysical constraints.Comment: 33 pages, latex. Corrections in eqs. 3.21, 3.23, 4.1, 4.5-10. One
figure adde
Direct CP Violation in B -> X_s gamma Decays as a Signature of New Physics
We argue that the observation of a sizable direct CP asymmetry A_{CP} in the
inclusive decays B -> X_s gamma would be a clean signal of New Physics. In the
Standard Model, A_{CP} can be calculated reliably and is found to be below 1%
in magnitude. In extensions of the Standard Model with new CP-violating
couplings, large CP asymmetries are possible without conflicting with the
experimental value of the branching ratio for the decays B -> X_s gamma. In
particular, large asymmetries arise naturally in models with enhanced
chromo-magnetic dipole operators. Some generic examples of such models are
explored and their implications for the semileptonic branching ratio and charm
yield in B decays discussed.Comment: several references added and some numerical results updated to
include QED corrections (version to appear in Physical Review D
Extra Dimensions at the Weak Scale and Deviations from Newtonian Gravity
We consider theories in which the Standard Model gauge fields propagate in
extra dimensions whose size is around the electroweak scale. The Standard Model
quarks and leptons may either be localized to a brane or propagate in the bulk.
This class of theories includes models of Scherk-Schwarz supersymmetry
breaking and universal extra dimensions. We consider the problem of stabilizing
the volume of the extra dimensions. We find that for a large class of
stabilization mechanisms the field which corresponds to fluctuations of the
volume remains light even after stabilization, and has a mass in the
eV range. In particular this is the case if stabilization does not involve
dynamics at scales larger than the cutoff of the higher dimensional Standard
Model, and if the effective theory below the compactification scale is four
dimensional. The mass of this field is protected against large radiative
corrections by the general covariance of the higher dimensional theory and by
the weakness of its couplings, which are Planck suppressed. Its couplings to
matter mediate forces whose strength is comparable to that of gravity and which
can give rise to potentially observable deviations from Newton's Law at
sub-millimeter distances. Current experiments investigating short distance
gravity can probe extra dimensions too small to be accessible to current
collider experiments. In particular for a single extra dimension stabilized by
the Casimir energy of the Standard Model fields compactification radii as small
as 5 inverse TeV are accessible to current sub-millimeter gravity experiments.Comment: Minor corrections, conclusions unchanged. References adde
Self-Breaking of the Standard Model Gauge Symmetry
If the gauge fields of the Standard Model propagate in TeV-size extra
dimensions, they rapidly become strongly coupled and can form scalar bound
states of quarks and leptons. If the quarks and leptons of the third generation
propagate in 6 or 8 dimensions, we argue that the most tightly bound scalar is
a composite of top quarks, having the quantum numbers of the Higgs doublet and
a large coupling to the top quark. In the case where the gauge bosons propagate
in a bulk of a certain volume, this composite Higgs doublet can successfully
trigger electroweak symmetry breaking. The mass of the top quark is correctly
predicted to within 20%, without the need to add a fundamental Yukawa
interaction, and the Higgs boson mass is predicted to lie in the range 165 -
230 GeV. In addition to the Higgs boson, there may be a few other scalar
composites sufficiently light to be observed at upcoming collider experiments.Comment: 26 pages, 4 figures, typos corrected, references adde
A Dark Matter candidate from Lorentz Invariance in 6 Dimensions
We study the unique 6 dimensional orbifold with chiral fermions where a
stable dark matter candidate is present due to Lorentz invariance on the
orbifold, with no additional discrete symmetries imposed by hand. We propose a
model of Universal Extra Dimensions where a scalar photon of few hundred GeV is
a good candidate for dark matter. The spectrum of the model is characteristic
of the geometry, and it has clear distinctive features compared to previous
models of Kaluza-Klein dark matter. The 5 dimensional limit of this model is
the minimal model of natural Kaluza-Klein dark matter. Notwithstanding the low
mass range preferred by cosmology, the model will be a challenge for the LHC
due to the relatively small splitting between the states in the same KK level.Comment: 37 pages, 6 figure
Schwinger-Dyson Analysis of Dynamical Symmetry Breaking on a Brane with Bulk Yang-Mills Theory
The dynamically generated fermion mass is investigated in the flat brane
world with (4+delta)-dimensional bulk space-time, and in the Randall-Sundrum
(RS) brane world. We consider the bulk Yang-Mills theory interacting with the
fermion confined on a four-dimensional brane. Based on the effective theory
below the reduced cutoff scale on the brane, we formulate the Schwinger-Dyson
equation of the brane fermion propagator. By using the improved ladder
approximation we numerically solve the Schwinger-Dyson equation and find that
the dynamical fermion mass is near the reduced cutoff scale on the brane for
the flat brane world with delta >= 3 and for the RS brane world. In RS brane
world KK excited modes of the bulk gauge field localized around the y = pi R
brane and it enhances the dynamical symmetry breaking on the brane. The decay
constant of the fermion and the anti-fermion composite operator can be taken to
be the order of the electroweak scale much smaller than the Planck scale.
Therefore electroweak mass scale can be realized from only the Planck scale in
the RS brane world due to the fermion and the anti-fermion pair condensation.
That is a dynamical realization of Randall-Sundrum model which solves the
weak-Planck hierarchy problem.Comment: 21 pages, 12 figures; typos corrected, references added and updated,
footnotes adde
THE INFLUENCE OF WHEAT AND MAIZE CULTURES ON ROTATION AND MONOCULTURE ON THE ENZYMATIC COMPONENTS OF THE SOIL
In order to better characterize the soil's vitality and to assess the fertility level, pedo-enzymatic tests are used along with biotic and / or chemical analyzes. Pedo-enzymatic activities are evaluated in the laboratory to determine the potentials of a soil to release the ammonium and phosphorus required for soil and plant micropopulation nutrition. Pedo-enzymatic processes (pedo-phosphatase, pedo-amidase) are ongoing, to the extent that environmental conditions are favorable. The soil samples taken in the study were harvested from the Am (0-20 cm) horizon of the N0P70 fertilized variant, from the following crops: wheat after soybean crops of a three-year rotation, maize coming from a 4-year field temporarely outside the crop rotation, and from monocultures of wheat and maize. From the data analyzed as a result of this study it results that the crop rotation influences the pedo-enzymatic components of the soil. Total pedo-phosphatase activity in wheat and maize cultivation (rotating) was superior, the results being in the value group compared to the total pedo-phosphatase activity of the soil under the wheat and maize monocultures where the result of the analyzes indicated a much lower, being in b. The total soil pedo-amidase activity of wheat cultivated with maize as a precursor plant was superior, the result being in the a
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