Casimir friction in terms of moving harmonic oscillators: equivalence between two different formulations

The Casimir friction problem can be dealt with in a simplified way by considering two harmonic oscillators moving with constant relative velocity. Recently we calculated the energy dissipation ΔE for such a case [Europhys. Lett. 91, 60003 (2010); Eur. Phys. J. D 61, 335 (2011)]. A recent study of Barton [New J. Phys. 12, 113044 (2010)] seemingly leads to a different result for the dissipation. If such a discrepancy really were true, it would imply a delicate difficulty for the basic theory of Casimir friction. In the present note we show that the expressions for ΔE are in fact physically equivalent, at T = 0.     

Casimir Energy of an Open String with Angle-Dependent Boundary Conditions

Journal of Experimental and Theoretical Physics - We consider an open string with ends laying on the two different solid beams (rods). This setup is equivalent to two scalar fields with a set of...     

Search for charmed hadrons in neutral strange particle events in pp interactions at 19 GeV/c

A search for charmed hadrons has been made in proton-proton interactions at 19 GeV/c using events with one or two observed neutral strange particles. No evidence for charmed particles has been found. Upper limits for their production cross sections are presented.     

Geometric divisors in normal local domains

Let A be the local ring at a point of a normal complex variety with completion $R=\stackrel{?}{A}$. Srinivas has asked about the possible images of the induced map $\mathrm{Cl}A\to \mathrm{Cl}R$ over all geometric local normal domains A with fixed completion R. We use Noether–Lefschetz theory to prove that all finitely generated subgroups are possible in some familiar cases. As a byproduct we show that every finitely generated abelian group appears as the class group of the local ring at the vertex of a cone over some smooth complex variety of each positive dimension.     

Casimir friction force between polarizable media

This work is a continuation of our recent series of papers on Casimir friction, for a pair of particles of low relative particle velocity. Each particle is modeled as a simple harmonic oscillator. Our basic method, as before, is the use of quantum mechanical statistical mechanics, involving the Kubo formula, at finite temperature. In this work we begin by analyzing the Casimir friction between two particles polarizable in all spatial directions, this being a generalization of our study in [J.S. Høye, I. Brevik, Europhys. Lett. 91, 60003 (2010)], which was restricted to a pair of particles with longitudinal polarization only. For simplicity the particles are taken to interact via the electrostatic dipole-dipole interaction. Thereafter, we consider the Casimir friction between one particle and a dielectric half-space, and also the friction between two dielectric half-spaces. Finally, we consider general polarizabilities (beyond the simple one-oscillator form), and show how friction occurs at finite temperature when finite frequency regions of the imaginary parts of polarizabilities overlap.     

Electromagnetic momentum conservation in media

That static electric and magnetic fields can store momentum may be perplexing, but is necessary to ensure total conservation of momentum. Simple situations in which such field momentum is transferred to nearby bodies and point charges have often been considered for pedagogical purposes, normally assuming vacuum surroundings. If dielectric media are involved, however, the analysis becomes more delicate, not least since one encounters the electromagnetic energy–momentum problem in matter, the ‘Abraham–Minkowski enigma’, of what the momentum is of a photon in matter. We analyze the momentum balance in three nontrivial examples obeying azimuthal symmetry, showing how the momentum conservation is satisfied as the magnetic field decays and momentum is transferred to bodies present. In the last of the examples, that of point charge outside a dielectric sphere in an infinite magnetic field, we find that not all of the field momentum is transferred to the nearby bodies; a part of the momentum appears to vanish as momentum flux towards infinity. We discuss this and other surprising observations which can be attributed to the assumption of magnetic fields of infinite extent. We emphasize how formal arguments of conserved quantities cannot determine which energy–momentum tensor is more “correct”, and each of our conservation checks may be performed equally well in the Minkowski or Abraham framework.     

Dark energy and cosmology with viscosity

The paper studies the features of dark energy in the Universe in the presence of background viscosity in the cosmological fluid. Basing on the physically reasonable assumption that the background fluid can depend on the scaling factor in the Friedmann Universe, we show a possibility of realizing phantom cosmology describing superacceleration of the Universe. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 82–86, May, 2006.     

Letter: Inflationary Dilatonic de Sitter Universe from Super Yang-Mills Theory Perturbed by Scalars and Spinors

In this paper a quantum N = 4 super Yang-Mills theory perturbed by dilaton-coupled scalars and spinor fields, is considered. The induced effective action for such a theory is calculated on a dilaton-gravitational background using the conformal anomaly found via the AdS/CFT correspondence. Considering such an effective action (using the large N method) as a quantum correction to the classical gravity action with cosmological constant, we study the effect from the dilaton on the scale factor (this corresponds to an inflationary universe without dilaton). It is shown that, depending on the initial conditions for the dilaton, the dilaton may slow down, or accelerate, the inflation process. At late times, the dilaton is decaying exponentially. Different possible cases corresponding to a dilatonic dS Universe are analyzed with respect to the equations of motion.