268 research outputs found
The specificity of searches for , and coming from extra dimensions
We discuss the specificity of searches for hypothetical ,
and bosons at hadron colliders in single top
quark and production and Drell-Yan processes assuming these
particles to be the Kaluza-Klein excitations of the gauge bosons of the
Standard Model. In this case any process mediated by is also mediated by
the whole KK tower of its excitations, whereas to the processes mediated by
and there is not only a contribution from their KK towers, but also
from that of the graviton. The contributions of the towers above ,
and and above the first excitation of the
graviton are included with the help of effective four-fermion Lagrangians. We
compute the cross-sections of these processes taking into account the
contributions of the Standard Model gauge bosons, of their first KK modes and
of the corresponding KK towers and discuss the impact of the interference
between them. For pp-collisions at the LHC with the center of mass energy 14
TeV we found specific changes of the distribution tails due to the interference
effects. Such a modification of distribution tails is characteristic for the
processes mediated by particles coming from extra dimensions and should always
be taken into account when looking for them.Comment: 14 pages, 12 figures, LaTeX. References added, figures added, text
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A non-standard matter distribution in the RS1 model and the coupling constant of the radion
In the zero mode approximation we solve exactly the equations of motion for
linearized gravity in the Randall-Sundrum model with a non-standard
distribution of matter in the neighbourhood of the negative tension brane. It
is shown that the form of this distribution can strongly affect the coupling of
the radion to matter. We believe that such a situation can arise in models with
a realistic mechanisms of matter localization.Comment: 12 pages, LaTe
Physical degrees of freedom in stabilized brane world models
We consider brane world models with interbrane separation stabilized by the
Goldberger-Wise scalar field. For arbitrary background, or vacuum
configurations of the gravitational and scalar fields in such models, we
construct the second variation Lagrangian, study its gauge invariance, find the
corresponding equations of motion and decouple them in a suitable gauge. We
also derive an effective four-dimensional Lagrangian for such models, which
describes the massless graviton, a tower of massive gravitons and a tower of
massive scalars. It is shown that for a special choice of the background
solution the masses of the graviton excitations may be of the order of a few
TeV, the radion mass of the order of 100 GeV, the inverse size of the extra
dimension being tens of GeV. In this case the coupling of the radion to matter
on the negative tension brane is approximately the same as in the unstabilized
model with the same values of the fundamental five-dimensional energy scale and
the interbrane distance.Comment: 17 pages, LaTeX, corrected typos, amended the normalization constants
of the scalar modes and their coupling constants to matte
Effective Lagrangians for physical degrees of freedom in the Randall-Sundrum model
We derive the second variation Lagrangian of the Randall-Sundrum model with
two branes, study its gauge invariance and diagonalize it in the unitary gauge.
We also show that the effective four-dimensional theory looks different on
different branes and calculate the observable mass spectra and the couplings of
the physical degrees of freedom of 5-dimensional gravity to matter.Comment: 22 pages, LaTeX, typos correcte
Ignition of premixed air/fuel mixtures by microwave steamer discharge
A variety of methods exists for fast and efficient combustion of air-fuel mixtures. In this study, a microwave subcritical streamer discharge is used to ignite propane-air mixtures at atmospheric pressure. The streamer is initiated at the inner surface of a dielectric tube with the help of a passive half-wave vibrator. By creating a network of ignition lines, the streamer discharge forms the network of burning channels with large total surface area. This leads to the apparent speed of combustion propagation along the cylinder in excess of 100 m/s, which is more than 200 times the laminar flame propagation speed. The axial propagation of the combustion front in a cylindrical tube filled with the air/propane mixture is investigated by high speed video recording in visible light. A simple model is presented to explain observed results
ENVIRONMENTALLY FRIENDLY METHOD OF GASEOUS FUEL COMBUSTION WITH THE USE OF QUASI-OPTICAL MICROWAVE
Subject of Research.The paper deals with the problem of developing low emission combustors operating on natural gas or LPG, to reduce emissions of nitrogen oxides NOx. The possibility of burning very lean fuel mixtures is studied. To initiate the ignition and combustion stabilization the discharge generated by the quasi-optical microwave is used. Main Results. Initiating ignition by streamer microwave discharge increases the rate of combustion and combustion efficiency about four times as compared with the conventional spark ignition. Streamer discharge ignition by very lean fuel-air mixture is demonstrated with the factor of oxiding agent excess greater than the limit of explosive range under normal conditions. According to indirect indicators, ignition by microwave discharge created by quasi-optical radiation is of non-thermal nature. Microwave discharge excites oxygen atoms, and intense ultra-violet radiation is generated as a result that causes formation of cold nonequilibrium plasma with avalanche growth of free electrons. Streamer discharge propagates at a speed of 5 km /s, so the initiation of the ignition occurs immediately throughout. The temperature of the fuel mixture at the point of ignition initiation does not exceed 400 К.There is no area with a temperature sufficient to initiate thermal Zeldovich mechanism of emission of nitrogen oxides. Combustion rate is high. As a result the Fenimore mechanism of "fast nitrogen oxides" has no chance to be progressing, and NOx emissions in appreciable quantities are excluded. Energy costs are comparable with spark ignition.Practical Relevance. The studied technology is designed for low emission internal combustion engines, power gas turbines, gas compressor units, fueled by natural gas
Multiple-stable anisotropic magnetoresistance memory in antiferromagnetic MnTe
Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic materials. Recently, experimental bistable memories have been realized using fully compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II–VI semiconductors. Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Neel vector aligned along one of the three magnetic easy axes. The robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states are unique properties of antiferromagnets
Linearized gravity on the Randall-Sundrum two-brane background with curvature terms in the action for the branes
We study gravitational perturbations in the Randall-Sundrum two-brane
background with scalar-curvature terms in the action for the branes, allowing
for positive as well as negative bulk gravitational constant. In the zero-mode
approximation, we derive the linearized gravitational equations, which have the
same form as in the original Randall-Sundrum model but with different
expressions for the effective physical constants. We develop a generic method
for finding tachyonic modes in the theory, which, in the model under
consideration, may exist only if the bulk gravitational constant is negative.
In this case, if both brane gravitational constants are nonzero, the theory
contains one or two tachyonic mass eigenvalues in the gravitational sector. If
one of the brane gravitational constants is set to zero, then either a single
tachyonic mass eigenvalue is present or tachyonic modes are totally absent
depending on the relation between the nonzero brane gravitational constant and
brane separation. In the case of negative bulk gravitational constant, the
massive gravitational modes have ghost-like character, while the massless
gravitational mode is not a ghost in the case where tachyons are absent.Comment: 23 pages, revtex, published versio
Stratification of the orbit space in gauge theories. The role of nongeneric strata
Gauge theory is a theory with constraints and, for that reason, the space of
physical states is not a manifold but a stratified space (orbifold) with
singularities. The classification of strata for smooth (and generalized)
connections is reviewed as well as the formulation of the physical space as the
zero set of a momentum map. Several important features of nongeneric strata are
discussed and new results are presented suggesting an important role for these
strata as concentrators of the measure in ground state functionals and as a
source of multiple structures in low-lying excitations.Comment: 22 pages Latex, 1 figur
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