410 research outputs found
Critical behavior of gravitating sphalerons
We examine the gravitational collapse of sphaleron type configurations in
Einstein--Yang--Mills--Higgs theory. Working in spherical symmetry, we
investigate the critical behavior in this model. We provide evidence that for
various initial configurations, there can be three different critical
transitions between possible endstates with different critical solutions
sitting on the threshold between these outcomes. In addition, we show that
within the dispersive and black hole regimes, there are new possible endstates,
namely a stable, regular sphaleron and a stable, hairy black hole.Comment: Latex, 14 pages, 8 figure
Neutral Plasma Oscillations at Zero Temperature
We use cold plasma theory to calculate the response of an ultracold neutral
plasma to an applied rf field. The free oscillation of the system has a
continuous spectrum and an associated damped quasimode. We show that this
quasimode dominates the driven response. We use this model to simulate plasma
oscillations in an expanding ultracold neutral plasma, providing insights into
the assumptions used to interpret experimental data [Phys. Rev. Lett. 85, 318
(2000)].Comment: 4.3 pages, including 3 figure
Cosmological Implications of Domain Walls due to Duality Invariant Moduli Sector of Superstring Vacua
We study cosmological implications of the duality ()
invariant potential for the compactification radius , arising in a class of
superstring vacua. We show that in spite of having only one minimum in the
fundamental domain of the field there are two types of non-supersymmetric
domain walls: one is associated with the discrete Peccei-Quinn symmetry , analogous to the axionic domain wall, and another one associated with the
noncompact symmetry , analogous to the domain walls. The first
one is bound by stringy cosmic strings. The scale of such domain walls is
governed by the scale of gaugino condensation ( GeV) in the
case of hidden gauge group), while the separation between minima is of
order . We discuss the formation of walls and their cosmological
implications: the walls must be gotten rid of, either by chopping by stringy
cosmic strings and/or inflation. Since there is no usual Kibble mechanism to
create strings, either one must assume they exist , or one must
conclude that string cosmologies require inflation. The non-perturbative
potential dealt with here appears not to give the needed inflationary epoch.Comment: 10p., 3 figures, not included, minor wording change
Donor states in modulation-doped Si/SiGe heterostructures
We present a unified approach for calculating the properties of shallow
donors inside or outside heterostructure quantum wells. The method allows us to
obtain not only the binding energies of all localized states of any symmetry,
but also the energy width of the resonant states which may appear when a
localized state becomes degenerate with the continuous quantum well subbands.
The approach is non-variational, and we are therefore also able to evaluate the
wave functions. This is used to calculate the optical absorption spectrum,
which is strongly non-isotropic due to the selection rules. The results
obtained from calculations for Si/SiGe quantum wells allow us to
present the general behavior of the impurity states, as the donor position is
varied from the center of the well to deep inside the barrier. The influence on
the donor ground state from both the central-cell effect and the strain arising
from the lattice mismatch is carefully considered.Comment: 17 pages, 10 figure
Novel Phases in the Field Induced Spin Density Wave State in (TMTSF)_2PF_6
Magnetoresistance measurements on the quasi one-dimensional organic conductor
(TMTSF)_2PF_6 performed in magnetic fields B up to 16T, temperatures T down to
0.12K and under pressures P up to 14kbar have revealed new phases on its P-B-T
phase diagram. We found a new boundary which subdivides the field induced spin
density wave (FISDW) phase diagram into two regions. We showed that a
low-temperature region of the FISDW diagram is characterized by a hysteresis
behavior typical for the first order transitions, as observed in a number of
studies. In contrast to the common believe, in high temperature region of the
FISDW phase diagram, the hysteresis and, hence, the first order transitions
were found to disappear. Nevertheless, sharp changes in the resistivity slope
are observed both in the low and high temperature domains indicating that the
cascade of transitions between different subphases exists over all range of the
FISDW state. We also found that the temperature dependence of the resistance
(at a constant B) changes sign at about the same boundary. We compare these
results with recent theoretical models.Comment: LaTex, 4 pages, 4 figure
Approximate Solution of the effective mass Klein-Gordon Equation for the Hulthen Potential with any Angular Momentum
The radial part of the effective mass Klein-Gordon equation for the Hulthen
potential is solved by making an approximation to the centrifugal potential.
The Nikiforov-Uvarov method is used in the calculations. Energy spectra and the
corresponding eigenfunctions are computed. Results are also given for the case
of constant mass.Comment: 12 page
Supersymmetric solutions of PT-/non-PT-symmetric and non-Hermitian Screened Coulomb potential via Hamiltonian hierarchy inspired variational method
The supersymmetric solutions of PT-symmetric and Hermitian/non-Hermitian
forms of quantum systems are obtained by solving the Schrodinger equation for
the Exponential-Cosine Screened Coulomb potential. The Hamiltonian hierarchy
inspired variational method is used to obtain the approximate energy
eigenvalues and corresponding wave functions.Comment: 13 page
Polarized interacting exciton gas in quantum wells and bulk semiconductors
We develop a theory to calculate exciton binding energies of both two- and
three-dimensional spin polarized exciton gases within a mean field approach.
Our method allows the analysis of recent experiments showing the importance of
the polarization and intensity of the excitation light on the exciton
luminescence of GaAs quantum wells. We study the breaking of the spin
degeneracy observed at high exciton density . Energy
level splitting betwen spin +1 and spin -1 is shown to be due to many-body
inter-excitonic exchange while the spin relaxation time is controlled by
intra-exciton exchange.Comment: Revtex, 4 figures sent by fax upon request by e-mai
Tomography of pairing symmetry from magnetotunneling spectroscopy -- a case study for quasi-1D organic superconductors
We propose that anisotropic -, -, or -wave pairing symmetries can be
distinguished from a tunneling spectroscopy in the presence of magnetic fields,
which is exemplified here for a model organic superconductor .
The shape of the Fermi surface (quasi-one-dimensional in this example) affects
sensitively the pairing symmetry, which in turn affects the shape (U or V) of
the gap along with the presence/absence of the zero-bias peak in the tunneling
in a subtle manner. Yet, an application of a magnetic field enables us to
identify the symmetry, which is interpreted as an effect of the Doppler shift
in Andreev bound states.Comment: 4 papegs, 4 figure
Approximate solution of the Duffin-Kemmer-Petiau equation for a vector Yukawa potential with arbitrary total angular momenta
The usual approximation scheme is used to study the solution of the
Duffin-Kemmer-Petiau (DKP) equation for a vector Yukawa potential in the
framework of the parametric Nikiforov-Uvarov (NU) method. The approximate
energy eigenvalue equation and the corresponding wave function spinor
components are calculated for arbitrary total angular momentum in closed form.
Further, the approximate energy equation and wave function spinor components
are also given for case. A set of parameter values is used to obtain the
numerical values for the energy states with various values of quantum levelsComment: 17 pages; Communications in Theoretical Physics (2012). arXiv admin
note: substantial text overlap with arXiv:1205.0938, and with
arXiv:quant-ph/0410159 by other author
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