Hybridization gap and anisotropic far-infrared optical conductivity of URu2Si2

We performed far-infrared optical spectroscopy measurements on the heavy fermion compound URu 2 Si 2 as a function of temperature. The light's electric-field was applied along the a-axis or the c-axis of the tetragonal structure. We show that in addition to a pronounced anisotropy, the optical conductivity exhibits for both axis a partial suppression of spectral weight around 12 meV and below 30 K. We attribute these observations to a change in the bandstructure below 30 K. However, since these changes have no noticeable impact on the entropy nor on the DC transport properties, we suggest that this is a crossover phenomenon rather than a thermodynamic phase transition.Comment: To be published in Physical Review

Pion-nucleus optical potential valid up to the DELTA-resonance region

We present in this article an optical potential for the $\pi$-nucleus interaction that can be used in various studies involving $\pi$-nucleus channels. Based on earlier treatments of the low energy $\pi$-nucleus optical potential, we have derived a potential expression applicable from threshold up to the $\Delta$-resonance region. We extracted the impulse approximation form for this potential from the $\pi-N$ scattering amplitude and then added to it kinematical and physical corrections. The kinematic corrections arise from transforming the impulse approximation expression from the $\pi-N$ center of mass frame to the $\pi$-nucleus center of mass frame, while the physical corrections arise mostly from the many-body nature of the $\pi$-nucleus interaction. By taking advantage of the experimental progress in our knowledge of the $\pi-N$ process, we have updated earlier treatments with parameters calculated from state-of-the-art experimental measurements.Comment: 23 pages, 12 figures. Accepted for publication in Physical Review

Lessons to be learned from the coherent photoproduction of pseudoscalar mesons

We study the coherent photoproduction of pseudoscalar mesons---particularly of neutral pions---placing special emphasis on the various sources that put into question earlier nonrelativistic-impulse-approximation calculations. These include: final-state interactions, relativistic effects, off-shell ambiguities, and violations to the impulse approximation. We establish that, while distortions play an essential role in the modification of the coherent cross section, the uncertainty in our results due to the various choices of optical-potential models is relatively small (of at most 30%). By far the largest uncertainty emerges from the ambiguity in extending the many on-shell-equivalent representations of the elementary amplitude off the mass shell. Indeed, relativistic impulse-approximation calculations that include the same pionic distortions, the same nuclear-structure model, and two sets of elementary amplitudes that are identical on-shell, lead to variations in the magnitude of the coherent cross section by up to factors of five. Finally, we address qualitatively the assumption of locality implicit in most impulse-approximation treatments, and suggest that the coherent reaction probes---in addition to the nuclear density---the polarization structure of the nucleus.Comment: Manuscript is 27 pages long and includes 11 eps figure

Dev Dyn

Ror2 is a receptor tyrosine kinase mutated in the human syndromes Brachydactyly type B (BDB) and recessive Robinow syndrome (RS). In this study, we used the chick as a model to investigate the role of Ror2 in skeletogenesis and to elucidate the functional consequences of Ror2 mutations. For this purpose, we cloned chicken Ror2 and analyzed its expression pattern at various embryonic stages by in situ hybridization and immunolabeling. We document expression of cRor2 in several organs, including mesonephros, heart, nervous system, intestine and cartilage. The high conservation of expression when compared with the mouse underlines the validity of the chick as a model system. Using replication-competent retroviral vector-mediated overexpression, we analyzed the functional consequences of truncating BDB and RS mutations in the developing chick limb. Overexpression of Ror2 mutants led to a disturbance of growth plate architecture and a severe block of chondrocyte differentiation, demonstrating the functional importance of Ror2 in skeletogenesis

Complementary reaction analyses and the isospin mixing of the 4- states in 16O

Data from the inelastic scattering of electrons, and of intermediate energy protons and pions leading to ``stretched'' configuration 4- states near 19 MeV excitation in 16O as well as from charge exchange (p,n) scattering to an isobaric analogue (4-) state in 16F have been analyzed to ascertain the degree of isospin mixing contained within those states and of the amount of d_{5/2}-p_{3/2}^{-1} particle-hole excitation strength they exhaust. The electron and proton scattering data have been analyzed using microscopic models of the structure and reactions, with details constrained by analyses of elastic scattering data.Comment: 25 pages, 12 figure

Rough paths in idealized financial markets

This paper considers possible price paths of a financial security in an idealized market. Its main result is that the variation index of typical price paths is at most 2, in this sense, typical price paths are not rougher than typical paths of Brownian motion. We do not make any stochastic assumptions and only assume that the price path is positive and right-continuous. The qualification "typical" means that there is a trading strategy (constructed explicitly in the proof) that risks only one monetary unit but brings infinite capital when the variation index of the realized price path exceeds 2. The paper also reviews some known results for continuous price paths and lists several open problems.Comment: 21 pages, this version adds (in Appendix C) a reference to new results in the foundations of game-theoretic probability based on Hardin and Taylor's work on hat puzzle

Progressive ataxia with oculo-palatal tremor and optic atrophy

The final publication is available at Springer via doi: 10.​1007/​s00415-013-7136-