Multipole modes and spin features in the Raman spectrum of nanoscopic quantum rings

We present a systematic study of ground state and spectroscopic properties of many-electron nanoscopic quantum rings. Addition energies at zero magnetic field (B) and electrochemical potentials as a function of B are given for a ring hosting up to 24 electrons. We find discontinuities in the excitation energies of multipole spin and charge density modes, and a coupling between the charge and spin density responses that allow to identify the formation of ferromagnetic ground states in narrow magnetic field regions. These effects can be observed in Raman experiments, and are related to the fractional Aharonov-Bohm oscillations of the energy and of the persistent current in the ring

Optimal generalized quantum measurements for arbitrary spin systems

Positive-operator-valued measurements on a finite number of N identically prepared systems of arbitrary spin J are discussed. Pure states are characterized in terms of Bloch-like vectors restricted by a SU(2J+1) covariant constraint. This representation allows for a simple description of the equations to be fulfilled by optimal measurements. We explicitly find the minimal positive-operator-valued measurement for the N=2 case, a rigorous bound for N=3, and set up the analysis for arbitrary N.

Hysteresis and avalanches in the T=0 random field ising model with 2-spin flip dynamics

We study the nonequilibrium behavior of the three-dimensional Gaussian random-field Ising model at T=0 in the presence of a uniform external field using a two-spin-flip dynamics. The deterministic, history-dependent evolution of the system is compared with the one obtained with the standard one-spin-flip dynamics used in previous studies of the model. The change in the dynamics yields a significant suppression of coercivity, but the distribution of avalanches (in number and size) stays remarkably similar, except for the largest ones that are responsible for the jump in the saturation magnetization curve at low disorder in the thermodynamic limit. By performing a finite-size scaling study, we find strong evidence that the change in the dynamics does not modify the universality class of the disorder-induced phase transition.

Spin-orbit effects in GaAs quantum wells: Interplay between Rashba, Dresselhaus, and Zeeman interactions

The interplay between Rashba, Dresselhaus, and Zeeman interactions in a quantum well submitted to an external magnetic field is studied by means of an accurate analytical solution of the Hamiltonian, including electron-electron interactions in a sum-rule approach. This solution allows us to discuss the influence of the spin-orbit coupling on some relevant quantities that have been measured in inelastic light scattering and electron-spin resonance experiments on quantum wells. In particular, we have evaluated the spin-orbit contribution to the spin splitting of the Landau levels and to the splitting of charge- and spin-density excitations. We also discuss how the spin-orbit effects change if the applied magnetic field is tilted with respect to the direction perpendicular to the quantum well.

Optical response of two-dimensional few-electron concentric double quantum rings: A local-spin-density-functional theory study

We have investigated the dipole charge- and spin-density response of few-electron two-dimensional concentric nanorings as a function of the intensity of a erpendicularly applied magnetic field. We show that the dipole response displays signatures associated with the localization of electron states in the inner and outer ring favored by the perpendicularly applied magnetic field. Electron localization produces a more fragmented spectrum due to the appearance of additional edge excitations in the inner and outer ring.

Exchange-correlation effects on quantum wires with spin-orbit interactions under the influence of in-plane magnetic fields.

Within the noncollinear local spin-density approximation, we have studied the ground state structure of a parabolically confined quantum wire submitted to an in-plane magnetic field, including both Rashba and Dresselhaus spin-orbit interactions. We have explored a wide range of linear electronic densities in the weak (strong) coupling regimes that appear when the ratio of spin-orbit to confining energy is small (large). These results are used to obtain the conductance of the wire. In the strong coupling limit, the interplay between the applied magnetic field¿irrespective of the in-plane direction, the exchange-correlation energy, and the spin-orbit energy-produces anomalous plateaus in the conductance vs linear density plots that are otherwise absent, or washes out plateaus that appear when the exchange-correlation energy is not taken into account.

Spin-orbit effects in GaAs quantum wells: Interplay between Rashba, Dresselhaus, and Zeeman interactions

The interplay between Rashba, Dresselhaus, and Zeeman interactions in a quantum well submitted to an external magnetic field is studied by means of an accurate analytical solution of the Hamiltonian, including electron-electron interactions in a sum-rule approach. This solution allows us to discuss the influence of the spin-orbit coupling on some relevant quantities that have been measured in inelastic light scattering and electron-spin resonance experiments on quantum wells. In particular, we have evaluated the spin-orbit contribution to the spin splitting of the Landau levels and to the splitting of charge- and spin-density excitations. We also discuss how the spin-orbit effects change if the applied magnetic field is tilted with respect to the direction perpendicular to the quantum well.

Spin polarized neutron matter and magnetic susceptibility within the Brueckner-Hartree-Fock approximation

The Brueckner-Hartree-Fock formalism is applied to study spin polarized neutron matter properties. Results of the total energy per particle as a function of the spin polarization and density are presented for two modern realistic nucleon-nucleon interactions, Nijmegen II and Reid93. We find that the dependence of the energy on the spin polarization is practically parabolic in the full range of polarizations. The magnetic susceptibility of the system is computed. Our results show no indication of a ferromagnetic transition which becomes even more difficult as the density increases.

Spin-2 gravitational trace anomaly

The part proportional to the Euler-Poincar characteristic of the contribution of spin-2 fields to the gravitational trace anomaly is computed. It is seen to be of the same sign as all the lower-spin contributions, making anomaly cancellation impossible. Subtleties related to Weyl invariance, gauge independence, ghosts, and counting of degrees of freedom are pointed out.

The QCD Potential at O(1/m2): Complete spin-dependent and spin-independent result

Within an effective field theory framework, we obtain an expression, with O(1/m2) accuracy, for the energies of the gluonic excitations between heavy quarks, which holds beyond perturbation theory. For the singlet heavy-quarkantiquark energy, in particular, we also obtain an expression in terms of Wilson loops. This provides, twenty years after the seminal work of Eichten and Feinberg, the first complete expression for the heavy quarkonium potential up to O(1/m2) for pure gluodynamics. Several errors present in the previous literature (also in the work of Eichten and Feinberg) have been corrected. We also briefly discuss the power counting of NRQCD in the nonperturbative regime.

Bax-induced apoptosis in Leber's congenital amaurosis : a dual role in rod and cone degeneration

Purpose:We previously observed that anti- and pro-apoptotic genes of the Bcl-2 family were differentially expressed during the development of LCA in the Rpe65-/- mouse model (Cottet et al. 2006). Moreover, we reported that activation and translocation of pro-apoptotic Bax to the mitochondria was associated with apoptosis of rod photoreceptors as the disease progressed (Cottet et al. 2008). In this study we challenged whether disruption of the pro-apoptotic pro-apoptotic Bax protein is sufficient to protect photoreceptor cells against apoptosis. Methods:Apoptosis of photoreceptor cells was addressed by TUNEL assay on flatmounted retinas. Counting of the rod nuclei within the ONL was performed following hematoxylin/eosin histological staining of retina sections. Expression level and localization of photoreceptor gene markers were assessed by quantitative PCR and immunohistological analyses. Results:While expression of rod photoreceptor genes was decreased in Rpe65-deficient retina, expression level remained unchanged in Rpe65-/- / Bax-/- mice. Moreover, OS dysorganization and shortening as well as decrease in ONL thickness observed in diseased retina were prevented in mice lacking functional Bax protein. TUNEL assay confirmed that Bax-dependent rod photoreceptor apoptosis was abolished in Rpe65-/- / Bax-/- mice. However, early and fast degeneration of cone cells was not prevented in Rpe65-/- / Bax-/- mice, indicating that Bax-induced apoptotic pathway was not involved in the degenerating process of cones in Rpe65-deficient retina. Conclusions:Altogether, these data show for the first time that a single genetic mutation can trigger two independent apoptotic pathways in rod and cone photoreceptors in LCA disease. While pro-apoptotic Bax is essential to trigger rod photoreceptor apoptosis, early degeneration of cones is not dependent on Bax-mediated apoptotic pathway in Rpe65-deficientmice.

Kinematically complete analysis of the CLAS data on the proton structure Function F2 in a Regge-Dual model

The recently measured inclusive electron-proton cross section in the nucleon resonance region, performed with the CLAS detector at the Thomas Jefferson Laboratory, has provided new data for the nucleon structure function F2 with previously unavailable precision. In this paper we propose a description of these experimental data based on a Regge-dual model for F2. The basic inputs in the model are nonlinear complex Regge trajectories producing both isobar resonances and a smooth background. The model is tested against the experimental data, and the Q2 dependence of the moments is calculated. The fitted model for the structure function (inclusive cross section) is a limiting case of the more general scattering amplitude equally applicable to deeply virtual Compton scattering. The connection between the two is discussed.

Diffractive J/Psi photoproduction in a dual model

J/psi photoproduction is studied in the framework of the analytic S-matrix theory. The differential and integrated elastic cross sections for J/psi photoproduction are calculated from a dual amplitude with Mandelstam analyticity. It is argued that, at low energies, the background, which is the low-energy equivalent of the high-energy diffraction, replaces the Pomeron exchange. The onset of the high-energy Pomeron dominance is estimated from the fits to the data.