Phonon dispersion and low energy anomaly in CaC6_6

We report measurements of phonon dispersion in CaC$_6$ using inelastic X-ray and neutron scattering. We find good overall agreement, particularly in the 50 meV energy region, between experimental data and first-principles density-functional-theory calculations. However, on the longitudinal dispersion along the $(1 1 1)$ axis of the rhombohedral representation, we find an unexpected anti-crossing with an additional longitudinal mode, at about 11 meV. At a comparable energy, we observe also unexpected intensity on the in-plane direction. These results resolve the previous incorrect assignment of a longitudinal phonon mode to a transverse mode in the same energy range. By calculating the electron susceptibility from first principles we show that this longitudinal excitation is unlikely to be due to a plasmon and consequently can probably be due to defects or vacancies present in the sample.Comment: Accepted for publication in Physical Review

Imprints of the Quantum World in Classical Mechanics

The imprints left by quantum mechanics in classical (Hamiltonian) mechanics are much more numerous than is usually believed. We show Using no physical hypotheses) that the Schroedinger equation for a nonrelativistic system of spinless particles is a classical equation which is equivalent to Hamilton's equations.Comment: Paper submitted to Foundations of Physic

Electron localization and possible phase separation in the absence of a charge density wave in single-phase 1T-VS2_2

We report on a systematic study of the structural, magnetic and transport properties of high-purity 1T-VS$_2$ powder samples prepared under high pressure. The results differ notably from those previously obtained by de-intercalating Li from LiVS$_2$. First, no Charge Density Wave (CDW) is found by transmission electron microscopy down to 94 K. Though, \textit{ab initio} phonon calculations unveil a latent CDW instability driven by an acoustic phonon softening at the wave vector ${\bf q}_{CDW} \approx$ (0.21,0.21,0) previously reported in de-intercalated samples. A further indication of latent lattice instability is given by an anomalous expansion of the V-S bond distance at low temperature. Second, infrared optical absorption and electrical resistivity measurements give evidence of non metallic properties, consistent with the observation of no CDW phase. On the other hand, magnetic susceptibility and NMR data suggest the coexistence of localized moments with metallic carriers, in agreement with \textit{ab initio} band structure calculations. This discrepancy is reconciled by a picture of electron localization induced by disorder or electronic correlations leading to a phase separation of metallic and non-metallic domains in the nm scale. We conclude that 1T-VS$_2$ is at the verge of a CDW transition and suggest that residual electronic doping in Li de-intercalated samples stabilizes a uniform CDW phase with metallic properties.Comment: 22 pages, 10 Figures. Full resolution pictures available at http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.23512

Link between laboratory and astrophysical radiative shocks

This work provides analytical solutions describing the post-shock structure of radiative shocks growing in astrophysics and in laboratory. The equations including a cooling function $\Lambda \propto \rho^{\epsilon} P^{\zeta} x^{\theta}$ are solved for any values of the exponents $\epsilon$, $\zeta$ and $\theta$. This modeling is appropriate to astrophysics as the observed radiative shocks arise in optically thin media. In contrast, in laboratory, radiative shocks performed using high-power lasers present a radiative precursor because the plasma is more or less optically thick. We study the post-shock region in the laboratory case and compare with astrophysical shock structure. In addition, we attempt to use the same equations to describe the radiative precursor, but the cooling function is slightly modified. In future experiments we will probe the PSR using X-ray diagnostics. These new experimental results will allow to validate our astrophysical numerical codes

Why are Prices Sticky? Evidence from Business Survey Data

This paper offers new insights on the price setting behaviour of German retail firms using a novel dataset that consists of a large panel of monthly business surveys from 1991-2006. The firm-level data allows matching changes in firms' prices to several other firm-characteristics. Moreover, information on price expectations allow analyzing the determinants of price updating. Using univariate and bivariate ordered probit specifications, empirical menu cost models are estimated relating the probability of price adjustment and price updating, respectively, to both time- and state- dependent variables. First, results suggest an important role for state-dependence; changes in the macroeconomic and institutional environment as well as firm-specific factors are significantly related to the timing of price adjustment. These findings imply that price setting models should endogenize the timing of price adjustment in order to generate realistic predictions concerning the transmission of monetary policy. Second, an analysis of price expectations yields similar results providing evidence in favour of state-dependent sticky plan models. Third, intermediate input cost changes are among the most important determinants of price adjustment suggesting that pricing models should explicitly incorporate price setting at different production stages. However, the results show that adjustment to input cost changes takes time indicating "additional stickiness" at the last stage of processing

Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering

We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 = 0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state, and generally agree with calculations with significant inelastic hadronic intermediate state contributions. A_n provides a direct probe of the imaginary component of the 2-gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.Comment: 5 pages, 3 figures, submitted to Physical Review Letters; shortened to meet PRL length limit, clarified some text after referee's comment

Strange Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment

We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < Q^2 < 1.0 GeV^2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange quark contributions to the currents of the proton. The measurements were made at JLab using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate non-zero, Q^2 dependent, strange quark contributions and provide new information beyond that obtained in previous experiments.Comment: 5 pages, 2 figure