Gauge Coupling Unification in GUT with Anomalous U(1) Symmetry

We show that in the framework of grand unified theory (GUT) with anomalous $U(1)_A$ gauge symmetry, the success of the gauge coupling unification in the minimal SU(5) GUT is naturally explained, even if the mass spectrum of superheavy fields does not respect SU(5) symmetry. Because the unification scale for most realizations of the theory becomes smaller than the usual GUT scale, it suggests that the present level of experiments is close to that sufficient to observe proton decay via dimension 6 operators, $p\to e+\pi$.Comment: 4 pages, RevTeX, to appear in Phys.Rev.Let

Mesoscopic magnetoelectric effect in chaotic quantum dots

The magnitude of the inverse Faraday effect (IFE), a static magnetization due to an ac electric field, can be strongly increased in a mesoscopic sample, sensitive to time-reversal symmetry (TRS) breaking. Random rectification of ac voltages leads to a magnetization flux, which can be detected by an asymmetry of Hall resistances in a multi-terminal setup. In the absence of applied magnetic field through a chaotic quantum dot the IFE scale, quadratic in voltage, is found as an analytic function of the ac frequency, screening, and coupling to the contacts and floating probes, and numerically it does not show any effect of spin-orbit interaction. Our results qualitatively agree with a recent experiment on TRS-breaking in a six-terminal Hall cross.Comment: 4+ pages, 2 figures; v2-published version, small change

Cotunneling through quantum dots coupled to magnetic leads: zero-bias anomaly for non-collinear magnetic configurations

Cotunneling transport through quantum dots weakly coupled to non-collinearly magnetized leads is analyzed theoretically by means of the real-time diagrammatic technique. The electric current, dot occupations, and dot spin are calculated in the Coulomb blockade regime and for arbitrary magnetic configuration of the system. It is shown that an effective exchange field exerted on the dot by ferromagnetic leads can significantly modify the transport characteristics in non-collinear magnetic configurations, in particular the zero-bias anomaly found recently for antiparallel configuration. For asymmetric Anderson model, the exchange field gives rise to precession of the dot spin, which leads to a nonmonotonic dependence of the differential conductance and tunnel magnetoresistance on the angle between magnetic moments of the leads. An enhanced differential conductance and negative TMR are found for certain non-collinear configurations.Comment: 12 pages, 9 figgure

Dynamic assessment and word learning

This is the author's accepted manuscript. The original is available at http://www.speechpathologyaustralia.org.au/publications/jcpslpPast studies indicate that standardized vocabulary tests may be insensitive to language impairments and may be culturally biased. Dynamic assessment may be used as an alternative or supplementary approach to measure a child's ability to learn words. Factors that may need to be manipulated in dynamic assessment include phonotactic probability (i.e. frequency of sound sequences) and neighborhood density (phonological similarity) cause past research suggests that children with typical development learn common-dense sound sequences more readily than rare-sparse. Incorporating these factors into dynamic assessment is illustrated

Effects of antiferromagnetic planes on the superconducting properties of multilayered high-Tc cuprates

We propose a mechanism for high critical temperature (T_c) in the coexistent phase of superconducting- (SC) and antiferromagnetic (AF) CuO_2 planes in multilayered cuprates. The Josephson coupling between the SC planes separated by an AF insulator (Mott insulator) is calculated perturbatively up to the fourth order in terms of the hopping integral between adjacent CuO_2 planes. It is shown that the AF exchange splitting in the AF plane suppresses the so-called pi-Josephson coupling, and the long-ranged 0-Josephson coupling leads to coexistence with a rather high value of T_c.Comment: 4 pages including 4 figure

Individual differences in the influence of phonological characteristics on expressive vocabulary development by young children

This is the author's accepted manuscript. The original is available at http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=465943&fulltextType=RA&fileId=S0305000906007458The current study attempts to differentiate effects of phonotactic probability (i.e. the likelihood of occurrence of a sound sequence), neighbourhood density (i.e. the number of phonologically similar words), word frequency, and word length on expressive vocabulary development by young children. Naturalistic conversational samples for three children (age 1;4–3;1) were obtained from CHILDES. In a backward regression analysis, phonotactic probability, neighbourhood density, word frequency, and word length were entered as possible predictors of ages of first production of words for each child. Results showed that the factors affecting first production of words varied across children and across word types. Specifically, word length affected ages of first production for all three children, whereas the other three variables affected only one child each. The implications of these findings for models of expressive vocabulary development are discussed

Effects of mechanical rotation on spin currents

We study the Pauli--Schr\"odinger equation in a uniformly rotating frame of reference to describe a coupling of spins and mechanical rotations. The explicit form of the spin-orbit interaction (SOI) with the inertial effects due to the mechanical rotation is presented. We derive equations of motion for a wavepacket of electrons in two-dimensional planes subject to the SOI. The solution is a superposition of two cyclotron motions with different frequencies and a circular spin current is created by the mechanical rotation.Comment: 4 pages, 2 figure

Kondo quantum dot coupled to ferromagnetic leads: Numerical renormalization group study

We systematically study the influence of ferromagnetic leads on the Kondo resonance in a quantum dot tuned to the local moment regime. We employ Wilson's numerical renormalization group method, extended to handle leads with a spin asymmetric density of states, to identify the effects of (i) a finite spin polarization in the leads (at the Fermi-surface), (ii) a Stoner splitting in the bands (governed by the band edges) and (iii) an arbitrary shape of the leads density of states. For a generic lead density of states the quantum dot favors being occupied by a particular spin-species due to exchange interaction with ferromagnetic leads leading to a suppression and splitting of the Kondo resonance. The application of a magnetic field can compensate this asymmetry restoring the Kondo effect. We study both the gate-voltage dependence (for a fixed band structure in the leads) and the spin polarization dependence (for fixed gate voltage) of this compensation field for various types of bands. Interestingly, we find that the full recovery of the Kondo resonance of a quantum dot in presence of leads with an energy dependent density of states is not only possible by an appropriately tuned external magnetic field but also via an appropriately tuned gate voltage. For flat bands simple formulas for the splitting of the local level as a function of the spin polarization and gate voltage are given.Comment: 18 pages, 18 figures, accepted for publication in PR