1,671 research outputs found
Dynamical Fermion Masses Under the Influence of Kaluza-Klein Fermions and a Bulk Abelian Gauge Field
The dynamical fermion mass generation on a 3-brane in the 5D space-time is
discussed in a model with bulk fermions in interaction with fermions on the
brane assuming the presence of a constant abelian gauge field component
in the bulk. We calculate the effective potential as a function of the fermion
masses and the gauge field component . The masses can be found from the
stationarity condition for the effective potential (the gap equation). We
formulate the equation for the mass spectrum of the 4D--fermions. The phases
with finite and vanishing fermion masses are studied and the dependence of the
masses on the radius of the 5th dimension is analyzed. The influence of the
-component of the gauge field on the symmetry breaking is considered both
when this field is a background parameter and a dynamical variable. The
critical values of the field, the coupling constant and the radius are
examined.Comment: 9 pages, 4 figure
Gravitation interaction with extra dimension and periodic structure of the hadron scattering amplitude
The behavior of the hadron scattering amplitude determined by the gravitation
interaction of hadron at high energies with impact of the KK-modes in d-brane
models of gravity is examined. The possible periodic structure of the
scattering amplitude and its dependence on the number of additional dimensions
are analyzed. The effects of the gravitational hadron form factors obtained
from the hadron eneralized parton distributions (GPDs) on the behavior of the
interaction potential and the scattering amplitude are analyzed. It is shown
that in most part the periodic structure comes from the approximation of our
calculations.Comment: 9 pages, 8 figures, talk on the Intern. Workshop "Bogoliubov
Readings", Dubna (2010); updated reference
First Order Calculation of the Inclusive Cross Section pp to ZZ by Graviton Exchange in Large Extra Dimensions
We calculate the inclusive cross section of double Z-boson production within
large extra dimensions at the Large Hadron Collider (LHC). Using perturbatively
quantized gravity in the ADD model we perform a first order calculation of the
graviton mediated contribution to the pp to ZZ cross section. At low energies
(e.g. Tevatron) this additional contribution is very small, making it virtually
unobservable, for a fundamental mass scale above 2500 GeV. At LHC energies
however, the calculation indicates that the ZZ-production rate within the ADD
model should differ significantly from the Standard Model if the new
fundamental mass scale would be below 15000 GeV. A comparison with the observed
production rate at the LHC might therefore provide direct hints on the number
and structure of the extra dimensions.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.
Probability for Primordial Black Holes in Multidimensional Universe with Nonlinear Scalar Curvature Terms
We investigate multi-dimensional universe with nonlinear scalar curvature
terms to evaluate the probability of creation of primordial black holes. For
this we obtain Euclidean instanton solution in two different topologies: (a)
- topology which does not accommodate primordial black holes and (b)
-topology which accommodates a pair of black holes. The
probability for quantum creation of an inflationary universe with a pair of
black holes has been evaluated assuming a gravitational action which is
described by a polynomial function of scalar curvature with or without a
cosmological constant () using the framework of semiclassical
approximation of Hartle-Hawking boundary conditions. We discuss here a class of
new gravitational instantons solution in the -theory which are relevant
for cosmological model building.Comment: 18 pages, no figure. accepted in Phys. Rev.
Enhanced spin-orbit scattering length in narrow Al_xGa_{1-x}N/GaN wires
The magnetotransport in a set of identical parallel AlGaN/GaN quantum wire
structures was investigated. The width of the wires was ranging between 1110 nm
and 340 nm. For all sets of wires clear Shubnikov--de Haas oscillations are
observed. We find that the electron concentration and mobility is approximately
the same for all wires, confirming that the electron gas in the AlGaN/GaN
heterostructure is not deteriorated by the fabrication procedure of the wire
structures. For the wider quantum wires the weak antilocalization effect is
clearly observed, indicating the presence of spin-orbit coupling. For narrow
quantum wires with an effective electrical width below 250 nm the weak
antilocalization effect is suppressed. By comparing the experimental data to a
theoretical model for quasi one-dimensional structures we come to the
conclusion that the spin-orbit scattering length is enhanced in narrow wires.Comment: 6 pages, 5 figure
Modified Newton's law, braneworlds, and the gravitational quantum well
Most of the theories involving extra dimensions assume that only the
gravitational interaction can propagate in them. In such approaches, called
brane world models, the effective, 4-dimensional, Newton's law is modified at
short as well as at large distances. Usually, the deformation of Newton's law
at large distances is parametrized by a Yukawa potential, which arises mainly
from theories with compactified extra dimensions. In many other models however,
the extra dimensions are infinite. These approaches lead to a large distance
power-law deformation of the gravitational newtonian potential , namely
, which is less studied in the literature. We
investigate here the dynamics of a particle in a gravitational quantum well
with such a power-law deformation. The effects of the deformation on the energy
spectrum are discussed. We also compare our modified spectrum to the results
obtained with the GRANIT experiment, where the effects of the Earth's
gravitational field on quantum states of ultra cold neutrons moving above a
mirror are studied. This comparison leads to upper bounds on and .Comment: 11 pages, 1 figur
On the Casimir effect for parallel plates in the spacetime with one extra compactified dimension
In this paper, the Casimir effect for parallel plates in the presence of one
compactified universal extra dimension is reexamined in detail. Having
regularized the expressions of Casimir force, we show that the nature of
Casimir force is repulsive if the distance between the plates is large enough,
which is disagree with the experimental phenomena.Comment: 7 pages, 3 figure
The Casimir Force in Randall Sundrum Models
We discuss and compare the effects of one extra dimension in the Randall
Sundrum models on the evaluation of the Casimir force between two parallel
plates. We impose the condition that the result reproduce the experimental
measurements within the known uncertainties in the force and the plate
separation, and get an upper bound kR < 20 if the curvature parameter k of
AdS_5 is equal to the Planck scale. Although the upper bound decreases as k
decreases, kR ~ 12, which is the required value for solving the hierarchy
problem, is consistent with the Casimir force measurements. For the case where
the 5th dimension is infinite, the correction to the Casimir force is very
small and negligible.Comment: 16 pages, 2 figures, references added, text improved, accepted for
publication in PR
A critical dimension for the stability of perfect fluid spheres of radiation
An analysis of radiating perfect fluid models with asymptotically AdS
boundary conditions is presented. Such scenarios consist of a spherical gas of
radiation (a "star") localised near the centre of the spacetime due to the
confining nature of the AdS potential. We consider the variation of the total
mass of the star as a function of the central density, and observe that for
large enough dimensionality, the mass increases monotonically with the density.
However in the lower dimensional cases, oscillations appear, indicating that
the perfect fluid model of the star is becoming unrealistic. We find the
critical dimension separating these two regimes to be eleven.Comment: 18 pages, 5 figures; v2 reference and footnote added; v3 slight
reordering of content, new section added with further analysis; v4 Final
version - small changes, including a new title, accepted for publication in
CQ
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
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