2,004 research outputs found

### Instabilities of Twisted Strings

A linear stability analysis of twisted flux-tubes (strings) in an SU(2)
semilocal theory -- an Abelian-Higgs model with two charged scalar fields with
a global SU(2) symmetry -- is carried out. Here the twist refers to a relative
phase between the two complex scalars (with linear dependence on, say, the $z$
coordinate), and importantly it leads to a global current flowing along the the
string. Such twisted strings bifurcate with the Abrikosov-Nielsen-Olesen (ANO)
solution embedded in the semilocal theory. Our numerical investigations of the
small fluctuation spectrum confirm previous results that twisted strings
exhibit instabilities whose amplitudes grow exponentially in time. More
precisely twisted strings with a single magnetic flux quantum admit a
continuous family of unstable eigenmodes with harmonic $z$ dependence, indexed
by a wavenumber $k\in[-k_{\rm m},k_{\rm m}]$. Carrying out a perturbative
semi-analytic analysis of the bifurcation, it is found that the purely
numerical results are very well reproduced. This way one obtains not only a
good qualitative description of the twisted solutions themselves as well as of
their instabilities, but also a quantitative description of the numerical
results. Our semi-analytic results indicate that in close analogy to the known
instability of the embedded ANO vortex a twisted string is also likely to
expand in size caused by the spreading out of its magnetic flux.Comment: 27 pages, 18 figures. Typos corrected, references adde

### Renormalization group approach to Fermi Liquid Theory

We show that the renormalization group (RG) approach to interacting fermions
at one-loop order recovers Fermi liquid theory results when the forward
scattering zero sound (ZS) and exchange (ZS$'$) channels are both taken into
account. The Landau parameters are related to the fixed point value of the
``unphysical'' limit of the forward scattering vertex. We specify the
conditions under which the results obtained at one-loop order hold at all order
in a loop expansion. We also emphasize the similarities between our RG approach
and the diagrammatic derivation of Fermi liquid theory.Comment: 4 pages (RevTex) + 1 postcript file, everything in a uuencoded file,
uses epsf (problem with the figure in the first version

### Interaction of a surface acoustic wave with a two-dimensional electron gas

When a surface acoustic wave propagates on the surface of a GaAs
semiconductor, coupling between electrons in the two-dimensional electron gas
beneath the interface and the elastic host crystal through piezoelectric
interaction will attenuate the SAW. The coupling coefficient is calculated for
the SAW propagating along an arbitrary direction. It is found that the coupling
strength is largely dependent on the propagating direction. When the SAW
propagates along the [011] direction, the coupling becomes quite weak.Comment: 3 figure

### High Density Effective Theory Confronts the Fermi Liquid

The high density effective theory recently introduced by Hong and Hsu to
describe ultradense relativistic fermionic matter is used to calculate the
tree-level forward scattering amplitude between two particles at the Fermi
surface. While the direct term correctly reproduces that of the underlying
gauge theory, the exchange term has the wrong sign. The physical consequences
are discussed in the context of Landau's theoretical description of the Fermi
liquid.Comment: 15 pages, 2 figures; conclusion expanded, reference adde

### Empirical Emission Functions for LPM Suppression of Photon Emission from Quark-Gluon Plasma

The LPM suppression of photon emission rates from the quark gluon plasma have
been studied at different physical conditions of the plasma given by
temperature and chemical potentials.The integral equation for the transverse
vector function (f(p_t)) consisting of multiple scattering effects is solved
for the parameter set {p,k,kappa,T}, for bremsstrahlung and AWS processes. The
peak positions of these distributions depend only on the dynamical variable
x=(T/kappa)|1/p-1/(p+k)|. Integration over these distributions multiplied by
x^2 factor also depends on this variable x,leading to a unique global emission
function g(x) for all parameters. Empirical fits to this dimensionless emission
function, g(x), are obtained. The photon emission rate calculations with LPM
suppression effects reduce to one dimensional integrals involving folding over
the empirical g(x) function with appropriate distribution functions and the
kinematic factors. Using this approach, the suppression factors for both
bremsstrahlung and AWS have been estimated for various chemical potentials and
compared with the variational method

### Realistic Electron-Electron Interaction in a Quantum Wire

The form of an effective electron-electron interaction in a quantum wire with
a large static dielectric constant is determined and the resulting properties
of the electron liquid in such a one-dimensional system are described. The
exchange and correlation energies are evaluated and a possibility of a
paramagnetic-ferromagnetic phase transition in the ground state of such a
system is discussed. Low-energy excitations are briefly described.Comment: 10 pages, 6 figure

### Mass singularity and confining property in $QED_3$

We discuss the properties of the position space fermion propagator in three
dimensional QED which has been found previouly based on Ward-Takahashi-identity
for soft-photon emission vertex and spectral representation.There is a new type
of mass singularity which governs the long distance behaviour.It leads the
propagator vanish at large distance.This term corresponds to dynamical mass in
position space.Our model shows confining property and dynamical mass generation
for arbitrary coupling constant.Since we used dispersion retation in deriving
spectral function there is a physical mass which sets a mass scale.For finite
cut off we obtain the full propagator in the dispersion integral as a
superposition of different massses.Low energy behaviour of the proagator is
modified to decrease by position dependent mass.In the limit of zero infrared
cut-off the propagator vanishes with a new kind of infrared behaviour.Comment: 22pages,4figures,revtex4,Notational sloppiness are crrected.Submitted
to JHE

### The quantum theory of the Penning trap

We present the quantum theory of the Penning trap in terms of individual x and y radial modes of the motion of a single charged particle in the trap, and demonstrate how the conventional rotating frame used to examine these individual dynamics fails in the quantum regime. In solving the radial Hamiltonian in the {x,y} basis, we show how canonical transformation of the variables must take place after quantization, in order that these separate motions can be consistently tracked. This is in contrast to previous work. The results of the discussion lend themselves to a fully quantum treatment of mode coupling in the trap, leading to an avoided crossing between the coupled energy levels of the system. Exploiting the algebraic structure of the problem allows employment of a dressed-atom formalism within quantum Penning trap theory, and future applications resulting from this are proposed

### Flat coordinates and dilaton fields for three--dimensional conformal sigma models

Riemannian coordinates for flat metrics corresponding to three--dimensional
conformal Poisson--Lie T--dualizable sigma models are found by solving partial
differential equations that follow from the transformations of the connection
components. They are then used for finding general forms of the dilaton fields
satisfying the vanishing beta equations of the sigma models.Comment: 16 pages, no figure

### The Equation of State for Cool Relativistic Two-Constituent Superfluid Dynamics

The natural relativistic generalisation of Landau's two constituent
superfluid theory can be formulated in terms of a Lagrangian $L$ that is given
as a function of the entropy current 4-vector $s^\rho$ and the gradient
$\nabla\varphi$ of the superfluid phase scalar. It is shown that in the ``cool"
regime, for which the entropy is attributable just to phonons (not rotons), the
Lagrangian function $L(\vec s, \nabla\varphi)$ is given by an expression of the
form $L=P-3\psi$ where $P$ represents the pressure as a function just of
$\nabla\varphi$ in the (isotropic) cold limit. The entropy current dependent
contribution $\psi$ represents the generalised pressure of the (non-isotropic)
phonon gas, which is obtained as the negative of the corresponding grand
potential energy per unit volume, whose explicit form has a simple algebraic
dependence on the sound or ``phonon" speed $c_P$ that is determined by the cold
pressure function $P$.Comment: 26 pages, RevTeX, no figures, published in Phys. Rev. D. 15 May 199

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