13,597 research outputs found
Nonequilibrium Fock space for the electron transport problem
Based on the formalism of thermo field dynamics we propose a concept of
nonequilibrium Fock space and nonequilibrium quasiparticles for quantum
many-body system in nonequilibrium steady state. We develop a general theory as
well as demonstrate the utility of the approach on the example of electron
transport through the interacting region. The proposed approach is compatible
with advanced methods of electronic structure calculations such as coupled
cluster theory and configuration interaction
Tunable pinning of a superconducting vortex a by a magnetic vortex
The interaction between a straight vortex line in a superconducting film and
a soft magnetic nanodisk in the magnetic vortex state in the presence of a
magnetic field applied parallel to the film surfaces is studied theoretically.
The superconductor is described by London theory and the nanodisk by the
Landau-Lifshitz continuum theory of magnetism, using the approximation known as
the rigid vortex model. Pinning of the vortex line by the nanodisk is found to
result, predominantly, from the interaction between the vortex line and the
changes in the nanodisk magnetization induced by the magnetic field of the
vortex line and applied field. In the context of the rigid vortex model, these
changes result from the displacement of the magnetic vortex. This displacement
is calculated analytically by minimizing the energy, and the pinning potential
is obtained. The applied field can tune the pinning potential by controlling
the displacement of the magnetic vortex. The nanodisk magnetization curve is
predicted to change in the presence of the vortex lineComment: 9 pages, 8 figures. Submitted to Phys. Rev.
Three-dimensional Roton-Excitations and Supersolid formation in Rydberg-excited Bose-Einstein Condensates
We study the behavior of a Bose-Einstein condensate in which atoms are weakly
coupled to a highly excited Rydberg state. Since the latter have very strong
van der Waals interactions, this coupling induces effective, nonlocal
interactions between the dressed ground state atoms, which, opposed to dipolar
interactions, are isotropically repulsive. Yet, one finds partial attraction in
momentum space, giving rise to a roton-maxon excitation spectrum and a
transition to a supersolid state in three-dimensional condensates. A detailed
analysis of decoherence and loss mechanisms suggests that these phenomena are
observable with current experimental capabilities.Comment: 4 pages, 5 figure
Semiclassical quantization of the Bogoliubov spectrum
We analyze the Bogoliubov spectrum of the 3-sites Bose-Hubbard model with
finite number of Bose particles by using a semiclassical approach. The
Bogoliubov spectrum is shown to be associated with the low-energy regular
component of the classical Hubbard model. We identify the full set of the
integrals of motions of this regular component and, quantizing them, obtain the
energy levels of the quantum system. The critical values of the energy, above
which the regular Bogoliubov spectrum evolves into a chaotic spectrum, is
indicated as well.Comment: 4.1 pages, 3 figure
On Inflation and Variation of the Strong Coupling Constant
Variation of constants in the very early universe can generate inflation. We
consider a scenario where the strong coupling constant was changing in time and
where the gluon condensate underwent a phase transition ending the inflation.Comment: 12 pages, 1 figure, accepted for publication in International Journal
of Modern Physics
Landau Damping in a Turbulent Setting
To address the problem of Landau damping in kinetic turbulence, the forcing
of the linearized Vlasov equation by a stationary random source is considered.
It is found that the time-asymptotic density response is dominated by resonant
particle interactions that are synchronized with the source. The energy
consumption of this response is calculated, implying an effective damping rate,
which is the main result of this paper. Evaluating several cases, it is found
that the effective damping rate can differ from the Landau damping rate in
magnitude and also, remarkably, in sign. A limit is demonstrated in which the
density and current become phase-locked, which causes the effective damping to
be negligible; this potentially resolves an energy paradox that arises in the
application of critical balance to a kinetic turbulence cascade.Comment: Introduction significantly expanded to help contextualize results.
Calculations unchange
A new modelling framework for statistical cumulus dynamics
We propose a new modelling framework suitable for the description of atmospheric convective systems as a collection of distinct plumes. The literature contains many examples of models for collections of plumes in which strong simplifying assumptions are made, a diagnostic dependence of convection on the large-scale environment and the limit of many plumes often being imposed from the outset. Some recent studies have sought to remove one or the other of those assumptions. The proposed framework removes both, and is explicitly time-dependent and stochastic in its basic character. The statistical dynamics of the plume collection are defined through simple probabilistic rules applied at the level of individual plumes, and van Kampen's system size expansion is then used to construct the macroscopic limit of the microscopic model. Through suitable choices of the microscopic rules, the model is shown to encompass previous studies in the appropriate limits, and to allow their natural extensions beyond those limits
Comment on "Acoustics of tachyon Fermi gas" [E. Trojan and G.V. Vlasov, arXiv:1103.2276 (hep-ph)]
In contrast to Trojan and Vlasov [arXiv:1103.2276 (hep-ph)], it is found that
an ideal Fermi gas of tachyons has a subluminous velocity of sound for any
particle density and, therefore, the causality condition for a tachyon gas
holds always true. Also, an ideal Fermi gas of tachyons never possesses an
exotic equation of state with the pressure exceeding the energy density.Comment: 1 page + Ref
Force on a moving point impurity due to quantum fluctuations in a Bose-Einstein condensate
An analytic expression is derived for a force on a weak point impurity
arising from the scattering of quantum fluctuations in a slow-moving, weakly
interacting, three-dimensional Bose-Einstein condensate at zero temperature. In
an infinitely extended geometry, this force is shown to exist at any
arbitrarily small flow velocity below Landau's critical velocity. Furthermore,
this force is shown to be directly proportional to the flow speed.Comment: v2: corrected notation and other minor change
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