Casimir energy of a dilute dispersive dielectric ball: realistic microscopic model

The Casimir energy of a dilute homogeneous nonmagnetic dielectric ball at zero temperature is derived analytically within a microscopic realistic model of dielectrics for an arbitrary physically possible frequency dispersion of dielectric permittivity. Divergences are absent in calculations, a minimum interatomic distance is a physical cut-off. Casimir surface force is proved to be attractive. A physical definition of the Casimir energy is discussed.Comment: Latex 2e, 4 pages, 1 figure, to appear in Int. J. Mod. Phys. A [a talk given at the Fifth Leipzig Workshop on Quantum Field Theory under the Influence of External Conditions, September 10-14, 2001

Surface-atom force out of thermal equilibrium and its effect on ultra-cold atoms

The surface-atom Casimir-Polder-Lifshitz force out of thermal equilibrium is investigated in the framework of macroscopic electrodynamics. Particular attention is devoted to its large distance limit that shows a new, stronger behaviour with respect to the equilibrium case. The frequency shift produced by the surface-atom force on the the center-of-mass oscillations of a harmonically trapped Bose-Einstein condensate and on the Bloch oscillations of an ultra-cold fermionic gas in an optical lattice are discussed for configurations out of thermal equilibrium.Comment: Submitted to JPA Special Issue QFEXT'0

Application of the Lifshitz theory to poor conductors

The Lifshitz formula for the dispersive forces is generalized to the materials, which cannot be described with the local dielectric response. Principal nonlocality of poor conductors is related with the finite screening length of the penetrating field and the collisional relaxation; at low temperatures the role of collisions plays the Landau damping. The spatial dispersion makes the theory self consistent. Our predictions are compared with the recent experiment. It is demonstrated that at low temperatures the Casimir-Lifshitz entropy disappears as $T$ in the case of degenerate plasma and as $T^2$ for the nondegenerate one.Comment: Accepted for publication in PR

Excitation of Longitudinal Waves in a Degenerate Isotropic Quantum Plasma

A dispersion equation, which describes the interaction of low density electron beam with a degenerate electron quantum plasma, is derived and examined for some interesting cases. In addition to the instabilities similar to those for classical plasma, due to the quantum effect a new type of instability is found. Growth rates of these new modes, which are purely quantum, are obtained. Furthermore, the excitation of Bogolyubov's type of spectrum by a strong electric field is discussed.Comment: Submitted to Journal of Plasma Physics special issu

Electromagnetic vacuum energy for two parallel slabs in terms of surface, wave guide and photonic modes

The formulation of the Lifshitz formula in terms of real frequencies is reconsidered for half spaces described by the plasma model. It is shown that besides the surface modes (for the TM polarization), and the photonic modes, also waveguide modes must be considered.Comment: some references adde

Dimensional-scaling estimate of the energy of a large system from that of its building blocks: Hubbard model and Fermi liquid

A simple, physically motivated, scaling hypothesis, which becomes exact in important limits, yields estimates for the ground-state energy of large, composed, systems in terms of the ground-state energy of its building blocks. The concept is illustrated for the electron liquid, and the Hubbard model. By means of this scaling argument the energy of the one-dimensional half-filled Hubbard model is estimated from that of a 2-site Hubbard dimer, obtaining quantitative agreement with the exact one-dimensional Bethe-Ansatz solution, and the energies of the two- and three-dimensional half-filled Hubbard models are estimated from the one-dimensional energy, recovering exact results for $U\to 0$ and $U\to \infty$ and coming close to Quantum Monte Carlo data for intermediate $U$.Comment: 3 figure

Casimir energy of dielectric systems

A new formula for the Casimir energy of a dispersive dilute dielectric ball is discussed. The formula for the Casimir energy of a polarizable particle situated in a perfectly conducting wedge-shaped cavity is derived by a path-integral coordinate space method in quantum field theory.Comment: Latex 2e, 4 pages, no figures, a talk given at the International Meeting "Quantum Gravity and Spectral Geometry" (Naples, Italy, July 2-7, 2001

Deformed Fermi Surface Theory of Magneto-Acoustic Anomaly in Modulated Quantum Hall Systems Near /nu=1/2/nu=1/2

We introduce a new generic model of a deformed Composite Fermion-Fermi Surface (CF-FS) for the Fractional Quantum Hall Effect near $/nu=1/2$ in the presence of a periodic density modulation. Our model permits us to explain recent Surface Acoustic Wave observations of anisotropic anomalies [1,2] in sound velocity and attenuation- appearance of peaks and anisotropy - which originate from contributions to the conductivity tensor due to regions of the CF-FS which are flattened by the applied modulation. The calculated magnetic field and wave vector dependence of the CF conductivity,velocity shift and attenuation agree with experiments.Comment: Revised manuscript (cond-mat/9807044) 23 September 1998; 10 page

Ferrimagnetic mixed-spin ladders in weak and strong coupling limits

We study two similar spin ladder systems with the ferromagnetic leg coupling. First model includes two sorts of spins, s= 1/2 and s= 1, and the second model comprises only s=1/2 legs coupled by a "triangular" rung exchange. The antiferromagnetic (AF) rung coupling destroys the long-range order and eventually makes the systems equivalent to the AF s=1/2 Heisenberg chain. We investigate the situation by different methods in weak and strong rung coupling limits. Particularly we compare the spin-wave theory and the bosonization method in the weak coupling regime of the second model. We analyze the spectra and correlations, and discuss the order parameter of these ladder systems.Comment: 12 pages, 4 figure

Berezinskii-Kosterlitz-Thouless transition in two-dimensional dipole systems

The superfluid to normal fluid transition of dipolar bosons in two dimensions is studied throughout the whole density range using path integral Monte Carlo simulations and summarized in the phase diagram. While at low densities, we find good agreement with the universal results depending only on the scattering length $a_s$, at moderate and high densities, the transition temperature is strongly affected by interactions and the elementary excitation spectrum. The results are expected to be of relevance to dipolar atomic and molecular systems and indirect excitons in quantum wells