84 research outputs found
Coexistence of Single and Double-Quantum Vortex Lines
We discuss the configurations in which singly and doubly quantized vortex
lines may coexist in a rotating superfluid. General principles of energy
minimization lead to the conclusion that in equilibrium the two vortex species
segregate within a cylindrical vortex cluster in two coaxial domains where the
singly quantized lines are in the outer annular region. This is confirmed with
simulation calculations on discrete vortex lines. Experimentally the
coexistence can be studied in rotating superfluid He-A. With cw NMR
techniques we find the radial distribution of the two vortex species to depend
on how the cluster is prepared: (i) By cooling through in rotation,
coexistence in the minimum energy configuration is confirmed. (ii) A glassy
agglomerate is formed if one starts with an equilibrium cluster of
single-quantum vortex lines and adds to it sequentially double-quantum lines,
by increasing the rotation velocity in the superfluid state. This proves that
the energy barriers, which separate different cluster configurations, are too
high for metastabilities to anneal.Comment: 12 pages, 11 figures; Changed content, 15 pages, 14 figure
Low-temperature nonequilibrium transport in a Luttinger liquid
The temperature-dependent nonlinear conductance for transport of a Luttinger
liquid through a barrier is calculated in the nonperturbative regime for
, where is the dimensionless interaction constant. To
describe the low-energy behavior, we perform a leading-log summation of all
diagrams contributing to the conductance which is valid for .
With increasing external voltage, the asymptotic low-temperature behavior
displays a turnover from the to a universal law.Comment: 13 pages RevTeX 3.0, accepted by Physical Review
Diagrammatic self-energy approximations and the total particle number
There is increasing interest in many-body perturbation theory as a practical tool for the calculation of ground-state properties. As a consequence, unambiguous sum rules such as the conservation of particle number under the influence of the Coulomb interaction have acquired an importance that did not exist for calculations of excited-state properties. In this paper we obtain a rigorous, simple relation whose fulfilment guarantees particle-number conservation in a given diagrammatic self-energy approximation. Hedin's G(0)W(0) approximation does not satisfy this relation and hence violates the particle-number sum rule. Very precise calculations for the homogeneous electron gas and a model inhomogeneous electron system allow the extent of the nonconservation to be estimated
Impact of eV-mass sterile neutrinos on neutrino-driven supernova outflows
Motivated by recent hints for sterile neutrinos from the reactor anomaly, we
study active-sterile conversions in a three-flavor scenario (2 active + 1
sterile families) for three different representative times during the
neutrino-cooling evolution of the proto-neutron star born in an
electron-capture supernova. In our "early model" (0.5 s post bounce), the
nu_e-nu_s MSW effect driven by Delta m^2=2.35 eV^2 is dominated by ordinary
matter and leads to a complete nu_e-nu_s swap with little or no trace of
collective flavor oscillations. In our "intermediate" (2.9 s p.b.) and "late
models" (6.5 s p.b.), neutrinos themselves significantly modify the nu_e-nu_s
matter effect, and, in particular in the late model, nu-nu refraction strongly
reduces the matter effect, largely suppressing the overall nu_e-nu_s MSW
conversion. This phenomenon has not been reported in previous studies of
active-sterile supernova neutrino oscillations. We always include the feedback
effect on the electron fraction Y_e due to neutrino oscillations. In all
examples, Y_e is reduced and therefore the presence of sterile neutrinos can
affect the conditions for heavy-element formation in the supernova ejecta, even
if probably not enabling the r-process in the investigated outflows of an
electron-capture supernova. The impact of neutrino-neutrino refraction is
strong but complicated, leaving open the possibility that with a more complete
treatment, or for other supernova models, active-sterile neutrino oscillations
could generate conditions suitable for the r-process.Comment: 23 pages, including 14 figures and 2 tables (minor changes in the
text). Matches published version in JCA
Approach to the semiconductor cavity QED in high-Q regimes with q-deformed boson
The high density Frenkel exciton which interacts with a single mode
microcavity field is dealed with in the framework of the q-deformed boson. It
is shown that the q-defomation of bosonic commutation relations is satisfied
naturally by the exciton operators when the low density limit is deviated. An
analytical expression of the physical spectrum for the exciton is given by
using of the dressed states of the cavity field and the exciton. We also give
the numerical study and compare the theoretical results with the experimental
resultsComment: 6 pages, 2 figure
Charge self-consistent dynamical mean-field theory based on the full-potential linear muffin-tin orbital method: methodology and applications
Full charge self-consistence (CSC) over the electron density has been
implemented into the local density approximation plus dynamical mean-field
theory (LDA+DMFT) scheme based on a full-potential linear muffin-tin orbital
method (FP-LMTO). Computational details on the construction of the electron
density from the density matrix are provided. The method is tested on the
prototypical charge-transfer insulator NiO using a simple static Hartree-Fock
approximation as impurity solver. The spectral and ground state properties of
bcc Fe are then addressed, by means of the spin-polarized T-matrix fluctuation
exchange solver (SPTF). Finally the permanent magnet SmCo is studied using
multiple impurity solvers, SPTF and Hubbard I, as the strength of the local
Coulomb interaction on the Sm and Co sites are drastically different. The
developed CSC-DMFT method is shown to in general improve on materials
properties like magnetic moments, electronic structure and the materials
density.Comment: 10 pages, 5 figure
Quantum Mechanics and Thermodynamics of Particles with Distance Dependent Statistics
The general notion of distance dependent statistics in anyon-like systems is
discussed. The two-body problem for such statistics is considered, the general
formula for the second virial coefficient is derived and it is shown that in
the limiting cases it reproduces the known results for ideal anyons.Comment: 9 pages, LATEX Kiev Institute for Theoretical Physics preprint
ITP-93-5E, January 199
Summing up the perturbation series in the Schwinger Model
Perturbation series for the electron propagator in the Schwinger Model is
summed up in a direct way by adding contributions coming from individual
Feynman diagrams. The calculation shows the complete agreement between
nonperturbative and perturbative approaches.Comment: 10 pages (in REVTEX
Towards a Nonequilibrium Quantum Field Theory Approach to Electroweak Baryogenesis
We propose a general method to compute -violating observables from
extensions of the standard model in the context of electroweak baryogenesis. It
is alternative to the one recently developed by Huet and Nelson and relies on a
nonequilibrium quantum field theory approach. The method is valid for all
shapes and sizes of the bubble wall expanding in the thermal bath during a
first-order electroweak phase transition. The quantum physics of -violation
and its suppression coming from the incoherent nature of thermal processes are
also made explicit.Comment: 19 pages, 1 figure available upon e-mail reques
Quasicondensate and superfluid fraction in the 2D charged-boson gas at finite temperature
The Bogoliubov - de Gennes equations are solved for the Coulomb Bose gas
describing a fluid of charged bosons at finite temperature. The approach is
applicable in the weak coupling regime and the extent of its quantitative
usefulness is tested in the three-dimensional fluid, for which diffusion Monte
Carlo data are available on the condensate fraction at zero temperature. The
one-body density matrix is then evaluated by the same approach for the
two-dimensional fluid with e^2/r interactions, to demonstrate the presence of a
quasi-condensate from its power-law decay with increasing distance and to
evaluate the superfluid fraction as a function of temperature at weak coupling.Comment: 9 pages, 2 figure
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