A theory of electromagnetic fluctuations for metallic surfaces and van der Waals interactions between metallic bodies

A new general expression is derived for the fluctuating electromagnetic field outside a metal surface, in terms of its surface impedance. It provides a generalization to real metals of Lifshitz theory of molecular interactions between dielectric solids. The theory is used to compute the radiative heat transfer between two parallel metal surfaces at different temperatures. It is shown that a measurement of this quantity may provide an experimental resolution of a long-standing controversy about the effect of thermal corrections on the Casimir force between real metal plates.Comment: 4 pages, 2 figures; typos corrected, minor changes to match the published version in Physical Review Letter

Finite size mean-field models

We characterize the two-site marginals of exchangeable states of a system of quantum spins in terms of a simple positivity condition. This result is used in two applications. We first show that the distance between two-site marginals of permutation invariant states on N spins and exchangeable states is of order 1/N. The second application relates the mean ground state energy of a mean-field model of composite spins interacting through a product pair interaction with the mean ground state energies of the components.Comment: 20 page

On the origin of the decrease in the torsional oscillator period of solid He4

A decrease in the rotational period observed in torsional oscillator measurements was recently taken as a possible indication of a supersolid state of helium. We reexamine this interpretation and note that the decrease in the rotation period is also consistent with a solidification of a small liquid-like component into a low-temperature glass. Such a solidification may occur by a low-temperature quench of topological defects (e.g., grain boundaries or dislocations) which we examined in an earlier work. The low-temperature glass can account for not only a monotonic decrease in the rotation period as the temperature is lowered but also explains the peak in the dissipation occurring near the transition point. Unlike the non-classical rotational inertia scenario, which depends on the supersolid fraction, the dependence of the rotational period on external parameters, e.g., the oscillator velocity, provides an alternate interpretation of the oscillator experiments. Future experiments might explore this effect.Comment: 10 pages, 3 figures; to appear in Phys. Rev.

Violation of the London Law and Onsager-Feynman quantization in multicomponent superconductors

Non-classical response to rotation is a hallmark of quantum ordered states such as superconductors and superfluids. The rotational responses of all currently known single-component "super" states of matter (superconductors, superfluids and supersolids) are largely described by two fundamental principles and fall into two categories according to whether the systems are composed of charged or neutral particles: the London law relating the angular velocity to a subsequently established magnetic field and the Onsager-Feynman quantization of superfluid velocity. These laws are theoretically shown to be violated in a two-component superconductor such as the projected liquid metallic states of hydrogen and deuterium at high pressures. The rotational responses of liquid metallic hydrogen or deuterium identify them as a new class of dissipationless states; they also directly point to a particular experimental route for verification of their existence.Comment: Nature Physics in print. This is an early version of the paper. The final version will be posted 6 months after its publication Nature Physics, according to the journal polic

Pair Production of Fourth Family Charged Sleptons at e+e−e^{+}e^{-} Colliders

We study the pair production of $\tilde{l}_{4}$, which is the supersymmetric partner of the fourth family charged lepton, at the $e^{+}e^{-}$ colliders. It is shown that the investigation of this process at ILC/CLIC will give opportunity to differentiate the MSSM with three and four families.Comment: 6 pages, 2 figure

Isotopic Dependence of the Casimir Force

We calculate the dependence of the Casimir force on the isotopic composition of the interacting objects. This dependence arises from the subtle influence of the nuclear masses on the electronic properties of the bodies. We discuss the relevance of these results to current experiments utilizing the iso-electronic effect to search at very short separations for new weak forces suggested by various unification theories.Comment: 12 pages, Revtex (to appear in Physical Review Letters

Exploring the role of professional associations in collective learning in London and New York's advertising and law professional service firm clusters.

The value of regional economies for collective learning has been reported by numerous scholars. However often work has been criticised for lacking analytical clarity and failing to explore the architectures of collective learning and the role of the knowledge produced in making firms in a cluster economy successful. This paper engages with these problematics and investigates how collective learning is facilitated in the advertising and law professional service firm clusters in London and New York. It explores the role of professional associations and investigates how they mediate a collective learning process in each city. It argues that professional associations seed urban communities of practice that emerge outside of the formal activities of professional associations. In these communities individual with shared interests in advertising and law learn from one-another and are therefore able to adapt and evolve one-another approaches to common industry challenges. The paper suggests this is another form of the variation Marshall highlighted in relation to cluster-based collective learning. The paper also shows how the collective learning process is affected by the presence, absence and strength of an institutional thickness. It is therefore argued that a richer understanding of institutional affects is needed in relation to CL

Extracting Weak Phase Information from B -> V_1 V_2 Decays

We describe a new method for extracting weak, CP-violating phase information, with no hadronic uncertainties, from an angular analysis of B -> V_1 V_2 decays, where V_1 and V_2 are vector mesons. The quantity $\sin^2 (2\beta + \gamma)$ can be cleanly obtained from the study of decays such as B_d^0(t) -> D^{*\pm} \rho^\mp, D^{*\pm} a_1^{\mp}, D^{*0} K^{*0}, etc. Similarly, one can use B_s^0(t) -> D_s^{*\pm} K^{*\mp} to extract $\sin^2 \gamma$. There are no penguin contributions to these decays. It is possible that $\sin^2 (2\beta + \gamma)$ will be the second function of CP phases, after $\sin 2\beta$, to be measured at B-factories.Comment: 4 pages, RevTeX, no figure

Statistical mechanics of an ideal Bose gas in a confined geometry

We study the behaviour of an ideal non-relativistic Bose gas in a three-dimensional space where one of the dimensions is compactified to form a circle. In this case there is no phase transition like that for the case of an infinite volume, nevertheless Bose-Einstein condensation signified by a sudden buildup of particles in the ground state can occur. We use the grand canonical ensemble to study this problem. In particular, the specific heat is evaluated numerically, as well as analytically in certain limits. We show analytically how the familiar result for the specific heat is recovered as we let the size of the circle become large so that the infinite volume limit is approached. We also examine in detail the behaviour of the chemical potential and establish the precise manner in which it approaches zero as the volume becomes large.Comment: 13 pages, 2 eps figures, revtex

Magnus and Iordanskii Forces in Superfluids

The total transverse force acting on a quantized vortex in a superfluid is a problem that has eluded a complete understanding for more than three decades. In this letter I propose a remarkably simple argument, somewhat reminiscent of Laughlin's beautiful argument for the quantization of conductance in the quantum Hall effect, to define the superfluid velocity part of the transverse force. This term is found to be $- \rho_s {\kappa}_s \times {v}_s$. Although this result does not seem to be overly controversial, this thermodynamic argument based only on macroscopic properties of the superfluid does offer a robust derivation. A recent publication by Thouless, Ao and Niu has demonstrated that the vortex velocity part of the transverse force in a homogeneous neutral superfluid is given by the usual form $\rho_s {\kappa}_s \times {v}_V$. A combination of these two independent results and the required Galilean invariance yields that there cannot be any transverse force proportional to the normal fluid velocity, in apparent conflict with Iordanskii's theory of the transverse force due to phonon scattering by the vortex.Comment: RevTex, 1 Encapsulated Postscript figur