2,386 research outputs found
Vacuum polarization energy of the Shifman-Voloshin soliton
We compute the vacuum polarization energy of soliton configurations in a
model with two scalar fields in one space dimension using spectral methods. The
second field represents an extension of the conventional kink soliton
model. We find that the vacuum polarization energy destabilizes the soliton
except when the fields have identical masses. In that case the model is
equivalent to two independent models.Comment: nine pape
Quantum stabilization of a hedgehog type of cosmic string
Within a slightly simplified version of the electroweak standard model we
investigate the stabilization of cosmic strings by fermion quantum
fluctuations. Previous studies of quantum energies considered variants of the
Nielsen-Olesen profile embedded in the electroweak gauge group and showed that
configurations are favored for which the Higgs vacuum expectation value drops
near the string core and the gauge field is suppressed. This work found that
the strongest binding was obtained from strings that differ significantly from
Nielsen-Olesen configurations, deforming essentially only the Higgs field in
order to generate a strong attraction without inducing large gradients.
Extending this analysis, we consider the leading quantum correction to the
energy per unit length of a hedgehog type string, which, in contrast to the
Nielsen-Olesen configuration, contains a pseudoscalar field. To employ the
spectral method we develop the scattering and bound state problems for fermions
in the background of a hedgehog string. Explicit occupation of bound state
levels leads to strings that carry the quantum numbers of the bound fermions.
We discuss the parameter space for which stable, hedgehog type cosmic strings
emerge and reflect on phenomenological consequences of these findings.Comment: 34 page
Attractive Electromagnetic Casimir Stress on a Spherical Dielectric Shell
Based on calculations involving an idealized boundary condition, it has long
been assumed that the stress on a spherical conducting shell is repulsive. We
use the more realistic case of a Drude dielectric to show that the stress is
attractive, matching the generic behavior of Casimir forces in
electromagnetism. We trace the discrepancy between these two cases to
interactions between the electromagnetic quantum fluctuations and the
dielectric material.Comment: Five pages, one figure, pdflatex, matches version to be pusblished in
Phys Lett
Spectral Methods for Coupled Channels with a Mass Gap
We develop a method to compute the vacuum polarization energy for coupled
scalar fields with different masses scattering off a background potential in
one space dimension. As an example we consider the vacuum polarization energy
of a kink-like soliton built from two real scalar fields with different mass
parameters.Comment: 14 pages, 5 figures, matches journal version, references added
(surprisingly many
Stable charged cosmic strings
We study the quantum stabilization of a cosmic string by a heavy fermion
doublet in a reduced version of the standard model. We show that charged
strings, obtained by populating fermionic bound state levels, become stable if
the electro--weak bosons are coupled to a fermion that is less than twice as
heavy as the top quark. This result suggests that extraordinarily large fermion
masses or unrealistic couplings are not required to bind a cosmic string in the
standard model. Numerically we find the most favorable string profile to be a
simple "trough" in the Higgs vev of radius . The
vacuum remains stable in our model, because neutral strings are not
energetically favored.Comment: 5 pages, 3 figures, version to be published in Phys. Rev. Let
Mobile Phone Power Amplifier Linearity and Efficiency Enhancement Using Digital Predistortion
The new generation mobile communication systems using spectrum efficient linear modulation schemes (QPSK,8PSK,QAM)need linear power amplifiers in the transmission path to have good ACPR and EVM values. Linearization methods can be used to increase the linearity of the power amplifiers (PA).However,it is not reasonable o use complicated,power consuming and high cost systems. This paper presents a digital predistortion implementation for WCDMA signals using an FPGA (Field Programmable Gate Array)as DSP and investigates the application of this system in handsets.The method applied requires minimum change in the conventional transmitter path configuration but considerable PAE improvement can be achieved
- …