Is it possible to intervene in the EPRB correlations?

The effect of a quasi-periodic shutter inserted between the source and one of the detectors in a correlated-photon type EPRB experiment is studied. It is shown that the time and polarization correlations are expected to disappear because an intermediate quantized field system is introduced by the shutter between the source field and the detector.     

Is the number of light flavors in QCD great?

At a qualitative level, it is well known that QCD featuring a large number of quark flavors must differ drastically from actual QCD. However, it is possible to consider the large-N_f limit (where N_f is the number of light flavors in QCD) such that the basic dynamics of the system remains unchanged. This is the region of chiral perturbation theory, where the limit N_f → ∞ is simultaneously the limit of a large number of colors, N_c. Features are indicated that make it possible, in such a situation, to compare analytically the same quantity in a simplified model of actual QCD and in the large-N_f limit, and methods are proposed for calculating these features. Calculations in the limit N_f → ∞ are of no use in assessing quantities of the theory at small N f.     

Is the proton electromagnetic form factor modified in nuclei?

Guided by the recent experimental confirmation of the validity of the Effective Momentum Approximation (EMA) in quasi-elastic scattering off nuclei, we have re-examined the extraction of the Longitudinal and Transverse Response Functions in medium-weight and heavy nuclei. In the EMA we have performed a Rosenbluth separation of the available world data on ⁴⁰Ca, ⁴⁸Ca, ⁵⁶Fe and ²⁰⁸Pb. We find that the Longitudinal Response Function for these nuclei is quenched and that the Coulomb sum is not saturated, at odds with recent claims in the literature.Received: 1 November 2002, Published online: 15 July 2003PACS: 25.30.Fj Inelastic electron scattering to continuum     

Is chiral symmetry restored in the excited meson spectrum?

The large degeneracy observed in the excited meson spectrum by the Cristal Barrel Collaboration in the experimental data on proton–antiproton annihilation in flight into mesons in the range 1.9–2.4 GeV has been interpreted as a signal of chiral symmetry restoration. In this work we suggest that such degeneracy may be an indication of the confinement potential modification by color screening. The experimental data can be fairly well reproduced in a constituent quark model with a screened linear confinement potential without changing the dynamical quark mass. Observables that could discriminate our model from those which explicitly restore the chiral symmetry are proposed.     

Is the unitarity of the quark-mixing CKM matrix violated in neutron beta-decay?

We report on a new measurement of neutron beta-decay asymmetry. From the result A(0) = -0.1189(7), we derive the ratio of the axial vector to the vector coupling constant lambda = g(A)/g(V) = -1.2739(19). When included in the world average for the neutron lifetime tau = 885.7(7) s, this gives the first element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix V(ud). With this value and the Particle Data Group values for V(us) and V(ub), we find a deviation from the unitarity condition for the first row of the CKM matrix of Delta = 0.0083(28), which is 3.0 times the stated error.     

Is the Lorentz signature of the metric of spacetime electromagnetic in origin?

We formulate a premetric version of classical electrodynamics in terms of the excitation and the field strength F=(E,B). A local, linear, and symmetric spacetime relation between H and F is assumed. It yields, if electric/magnetic reciprocity is postulated, a Lorentzian metric of spacetime thereby excluding Euclidean signature (which is, nevertheless, discussed in some detail). Moreover, we determine the Dufay law (repulsion of like charges and attraction of opposite ones), the Lenz rule (the relative sign in Faraday’s law), and the sign of the electromagnetic energy. In this way, we get a systematic understanding of the sign rules and the sign conventions in electrodynamics. The question in the title of the paper is answered affirmatively.     

Is all-electrical silicon quantum computing feasible in the long term?

The development of the first generation of commercial quantum computers is based on superconductive qubits and trapped ions respectively. Other technologies such as semiconductor quantum dots, neutral ions and photons could in principle provide an alternative to achieve comparable results in the medium term. It is relevant to evaluate if one or more of them is potentially more effective to address scalability to millions of qubits in the long term, in view of creating a universal quantum computer. We review an all-electrical silicon spin qubit, that is the double quantum dot hybrid qubit, a quantum technology which relies on both solid theoretical grounding on one side, and massive fabrication technology of nanometric scale devices by the existing silicon supply chain on the other.     

Uncertainty relations in quantum optics. Is the photon intelligent?

The Robertson–Schrödinger, Heisenberg–Robertson and Trifonov uncertainty relations for arbitrary two functions f₁$f_1$ and f₂$f_2$ depending on the quantum phase and the number of photons respectively, are given. Intelligent states and states which minimize locally the product of uncertainties (Δf₁)²⋅(Δf₂)²${\left(\Delta f_1\right)}^2\cdot {\left(\Delta f_2\right)}^2$ or the sum (Δf₁)²+(Δf₂)²${\left(\Delta f_1\right)}^2+{\left(\Delta f_2\right)}^2$ are investigated for the cases f₁=?,exp(i?),exp(−i?),cos?,sin?$f_1=?,exp\left(i?\right),exp(-i?),cos?,sin?$ and f₂=n$f_2=n$.     

Is multiscaling an artifact in the stochastically forced Burgers equation?

We study turbulence in the one-dimensional Burgers equation with a white-in-time, Gaussian random force that has a Fourier-space spectrum approximately 1/k, where k is the wave number. From very high-resolution numerical simulations, in the limit of vanishing viscosity, we find evidence for multiscaling of velocity structure functions which cannot be falsified by standard tests. We find a new artifact in which logarithmic corrections can appear disguised as anomalous scaling and conclude that bifractal scaling is likely.     

Is the 4.742 MeV state in 88Sr the 1− two-phonon state?

A nuclear resonance fluorescence experiment on ⁸⁸Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy. The γ-ray linear polarisation has been measured with a EUROBALL CLUSTER detector used as a Compton polarimeter. The results indicate positive parity for the J= 1 state at 4.742 MeV in ⁸⁸Sr, in contrast to the previous interpretation as a 1⁻ two-phonon (2⁺ ₁⊗ 3⁻ ₁) state and in conflict with the predictions of the quasiparticle-phonon model. On the basis of such calculations the 1⁺ state at 3.486 MeV may be considered as the 1⁺ ₁ one-phonon state and the very strong 1⁺ ₁→ 0⁺ ₁ deexcitation as proton spin-flip 2p_1/2→ 2p_3/2 transition. Received: 3 November 1999     

Is the universe homogeneous and isotropic in the time when quark-gluon plasma exists?

In this study, quark and strange quark matter which exist in the first seconds of the early Universe have been studied in the context of general relativity to be able to obtain space–time geometry of first seconds of the early Universe. For this purpose, Einstein’s field equations for quark and strange quark matter in the non static spherically symmetric space–time have been solved by using experimental result that anisotropy parameter of quark matter is very small. We have concluded from obtained solutions that the space–time structure of first seconds of the Early Universe is homogeneous and isotropic. Also we have concluded that the color interactions of the quarks may be origin of primordial magnetic field in the early universe.     

Is the elongation of Ge huts in the low-temperature regime governed by kinetics?

Contrary to pyramids and domes, elongated huts on a Si(001) substrate are commonly considered as kinetically limited structures. In this work, however, based on detailed scanning tunneling microscopy observations of Ge huts growing on Si(001) at temperatures below 550 degrees C and finite element analysis, the possibility of an equilibrium-driven elongation is raised, where hut-preceding pits are thought to lift the energetic degeneracy of {105} facets and cause elongation along energetically preferred directions.