1,826 research outputs found
Threshold production of meta-stable bound states of Kaluza Klein excitations in Universal Extra Dimensions
We study the formation and detection at the next linear e^+e^- collider of
bound states of level-1 quark Kaluza-Klein excitations B_KK within a scenario
of universal extra-dimensions (UED). The interactions of such Kaluza-Klein
excitations are modeled by an alpha_s driven Coulomb potential. In order to
obtain the threshold cross-section, we employ the Green function method which
is known to properly describe the peaks below threshold and to yield a net
increase in the continuum region (above threshold) relative to the naive Born
cross-section. We study such effect at different values of the scale (R^-1) of
the extra-dimensions with an explicit calculation of the mass spectrum as given
by radiative corrections. The overall effect is roughly 2.7 at R^-1=300 GeV and
goes down to 2.2 at R^-1=1000 GeV and a relatively large number of events is
expected from N_events ~ 2.5*10^4 at R^-1=300 GeV down to N_events ~ 10^3 at
R^-1=1000 GeV at the anticipated annual integrated luminosity of L_0= 100
fb^-1. We finally discuss some potentially observable signatures such as the
multilepton channels 2j + 2l + missing energy, and 2j + 4l + missing energy for
which we estimate statistical significance >~ 2 for R^-1 up to 600 ~ 700 GeV.Comment: Accepted for publication in Phys. Rev. D. Enhanced version. 13 pages,
5 figures, 2 table
Analytic pulse design for selective population transfer in many-level quantum systems: maximizing amplitude of population oscillations
State selective preparation and manipulation of discrete-level quantum
systems such as atoms, molecules or quantum dots is a the ultimate tool for
many diverse fields such as laser control of chemical reactions, atom optics,
high-precision metrology and quantum computing. Rabi oscillations are one of
the simplest, yet potentially quite useful mechanisms for achieving such
manipulation. Rabi theory establishes that in the two-level systems resonant
drive leads to the periodic and complete population oscillations between the
two system levels. In this paper an analytic optimization algorithm for
producing Rabi-like oscillations in the general discrete many-level quantum
systems is presented.Comment: Published in Phys.Rev.A. This is the final published versio
Brane Cosmology in an Arbitrary Number of Dimensions
We derive the effective cosmological equations for a non-
symmetric codimension one brane embedded in an arbitrary D-dimensional bulk
spacetime, generalizing the cases much studied previously. As a
particular case, this may be considered as a regularized codimension (D-4)
brane avoiding the problem of curvature divergence on the brane. We apply our
results to the case of spherical symmetry around the brane and to partly
compactified AdS-Schwarzschild bulks.Comment: 23 page
Weak antilocalization in a polarization-doped AlxGa1-xN/GaN heterostructure with single subband occupation
Spin-orbit scattering in a polarization-doped Al0.30Ga0.70N/GaN two-dimensional electron gas with one occupied subband is studied at low temperatures. At low magnetic fields weak antilocalization is observed, which proves that spin-orbit scattering occurs in the two-dimensional electron gas. From measurements at various temperatures the elastic scattering time tau(tr), the dephasing time tau(phi), and the spin-orbit scattering time tau(so) are extracted. Measurements in tilted magnetic fields were performed, in order to separate spin and orbital effects
The R.I. Pimenov unified gravitation and electromagnetism field theory as semi-Riemannian geometry
More then forty years ago R.I. Pimenov introduced a new geometry --
semi-Riemannian one -- as a set of geometrical objects consistent with a
fibering He suggested the heuristic principle according to
which the physically different quantities (meter, second, coulomb etc.) are
geometrically modelled as space coordinates that are not superposed by
automorphisms. As there is only one type of coordinates in Riemannian geometry
and only three types of coordinates in pseudo-Riemannian one, a multiple
fibered semi-Riemannian geometry is the most appropriate one for the treatment
of more then three different physical quantities as unified geometrical field
theory.
Semi-Euclidean geometry with 1-dimensional fiber and
4-dimensional Minkowski space-time as a base is naturally interpreted as
classical electrodynamics. Semi-Riemannian geometry with the
general relativity pseudo-Riemannian space-time and 1-dimensional
fiber responsible for the electromagnetism, provides the unified field
theory of gravitation and electromagnetism. Unlike Kaluza-Klein theories, where
the 5-th coordinate appears in nondegenerate Riemannian or pseudo-Riemannian
geometry, the theory based on semi-Riemannian geometry is free from defects of
the former. In particular, scalar field does not arise.
PACS: 04.50.Cd, 02.40.-k, 11.10.KkComment: 16 pages, 2 figures. Submited to Physics of Atomic Nucle
Variational formulation of Eisenhart's unified theory
Eisenhart's classical unified field theory is based on a non-Riemannian
affine connection related to the covariant derivative of the electromagnetic
field tensor. The sourceless field equations of this theory arise from
vanishing of the torsion trace and the symmetrized Ricci tensor. We formulate
Eisenhart's theory from the metric-affine variational principle. In this
formulation, a Lagrange multiplier constraining the torsion becomes the source
for the Maxwell equations.Comment: 7 pages; published versio
Dynamical Compactification and Inflation in Einstein-Yang-Mills Theory with Higher Derivative Coupling
We study cosmology of the Einstein-Yang-Mills theory in ten dimensions with a
quartic term in the Yang-Mills field strength. We obtain analytically a class
of cosmological solutions in which the extra dimensions are static and the
scale factor of the four-dimensional Friedmann-Lemaitre-Robertson-Walker metric
is an exponential function of time. This means that the model can explain
inflation. Then we look for solutions that describe dynamical compactification
of the extra dimensions. The effective cosmological constant in the
four-dimensional universe is determined from the gravitational coupling,
ten-dimensional cosmological constant, gauge coupling and higher derivative
coupling. By numerical integration, the solution with is found to
behave as a matter-dominated universe which asymptotically approaches flat
space-time, while the solution with a non-vanishing approaches de
Sitter space-time in the asymptotic future.Comment: 30 pages, 7 figure
Quantitative shadowgraphy and proton radiography for large intensity modulations
Shadowgraphy is a technique widely used to diagnose objects or systems in
various fields in physics and engineering. In shadowgraphy, an optical beam is
deflected by the object and then the intensity modulation is captured on a
screen placed some distance away. However, retrieving quantitative information
from the shadowgrams themselves is a challenging task because of the non-linear
nature of the process. Here, a novel method to retrieve quantitative
information from shadowgrams, based on computational geometry, is presented for
the first time. This process can be applied to proton radiography for electric
and magnetic field diagnosis in high-energy-density plasmas and has been
benchmarked using a toroidal magnetic field as the object, among others. It is
shown that the method can accurately retrieve quantitative parameters with
error bars less than 10%, even when caustics are present. The method is also
shown to be robust enough to process real experimental results with simple pre-
and post-processing techniques. This adds a powerful new tool for research in
various fields in engineering and physics for both techniques
Riemann-Einstein Structure from Volume and Gauge Symmetry
It is shown how a metric structure can be induced in a simple way starting
with a gauge structure and a preferred volume, by spontaneous symmetry
breaking. A polynomial action, including coupling to matter, is constructed for
the symmetric phase. It is argued that assuming a preferred volume, in the
context of a metric theory, induces only a limited modification of the theory.Comment: LaTeX, 13 pages; Added additional reference in Reference
Lorentz-breaking effects in scalar-tensor theories of gravity
In this work, we study the effects of breaking Lorentz symmetry in
scalar-tensor theories of gravity taking torsion into account. We show that a
space-time with torsion interacting with a Maxwell field by means of a
Chern-Simons-like term is able to explain the optical activity in syncrotron
radiation emitted by cosmological distant radio sources. Without specifying the
source of the dilaton-gravity, we study the dilaton-solution. We analyse the
physical implications of this result in the Jordan-Fierz frame. We also analyse
the effects of the Lorentz breaking in the cosmic string formation process. We
obtain the solution corresponding to a cosmic string in the presence of torsion
by keeping track of the effects of the Chern-Simons coupling and calculate the
charge induced on this cosmic string in this framework. We also show that the
resulting charged cosmic string gives us important effects concerning the
background radiation.The optical activity in this case is also worked out and
discussed.Comment: 10 pages, no figures, ReVTex forma
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