Is there a Di-Ω State?

Resonating-group method has been applied to calculate the ΩΩ (SIJ = -6,0,0) dibaryon state in theframework of the extended quark-delocalization color-screening model. The mass of the di-Ω is predicted to be about45 MeV lower than the Ω-Ω threshold. The effect of channel coupling due to the tensor force and sensitivity to mesonexchange short-range cutoff radius, ro have also been studied.     

Is there contextuality for a single qubit?

Cabello and Nakamura have shown [A. Cabello, Phys. Rev. Lett. 90, 190401 (2003)10.1103/PhysRevLett.90.190401] that the Kochen-Specker theorem can be applied to two-dimensional systems if one uses positive operator-valued measures (POVM). We show that the contextuality in their models is not of the Kochen-Specker type, but it is rather a result of not keeping track of the whole system on which the measurement is performed. This is connected to the fact that there is no one-to-one correspondence between the POVM elements and projectors on the extended Hilbert space, and the same POVM element has to originate from two different projectors when used in Cabello-Nakamura models. Moreover, we propose a hidden-variable formulation of the above models.     

Is there a c-theorem in four dimensions?

The difficulties of extending Zamolodchikov's c-theorem to dimensions d ≠ 2 are discussed. It is shown that, for d even, the one-point function of the trace of the stress tensor on the sphere, S^d, when suitably regularized, defines a c-function, which, at least to one loop order, is decreasing along RG trajectories and is stationary at RG fixed points, where it is proportional to the usual conformal anomaly. It is shown that the existence of such a c-function, if it satisfies these properties to all orders, is consistent with the expected behavior of QCD in four dimensions.     

Is there a reentrant glass in binary mixtures?

By employing computer simulations for a model binary mixture, we show that a reentrant glass transition upon adding a second component occurs only if the ratio alpha of the short-time mobilities between the glass-forming component and the additive is sufficiently small. For alpha approximately 1, there is no reentrant glass, even if the size asymmetry between the two components is large, in accordance with the two-component mode-coupling theory. For alpha<1, on the other hand, the reentrant glass is observed and reproduced only by an effective one-component mode-coupling theory.     

Is the Luttinger Liquid a New State of Matter?

We are demonstrating that the Luttinger model with short range interaction can be treated as a type of Fermi liquid. In line with the main dogma of Landau’s theory one can define a fermion excitation renormalized by interaction and show that in terms of these fermions any excited state of the system is described by free particles. The fermions are a mixture of renormalized right and left electrons. The electric charge and chirality of the Landau quasi-particle is discussed.     

What Is the State of a Hydrogen Atom Leaving a Stern-Gerlach Interferometer?

We discuss experimental results on Stern-Gerlachinterferometry with atoms. After a theoretical approachsuited for fast atoms, we discuss elementary experimentson the preservation of atomic coherence. Then we examine the action of theinterferometer as producing atoms with new properties,beaded atoms, and their radiative properties.     

Is there a shift to “active nanostructures”?

It has been suggested that an important transition in the long-run trajectory of nanotechnology development is a shift from passive to active nanostructures. Such a shift could present different or increased societal impacts and require new approaches for risk assessment. An active nanostructure “changes or evolves its state during its operation,” according to the National Science Foundation’s (2006) Active Nanostructures and Nanosystems grant solicitation. Active nanostructure examples include nanoelectromechanical systems (NEMS), nanomachines, self-healing materials, targeted drugs and chemicals, energy storage devices, and sensors. This article considers two questions: (a) Is there a “shift” to active nanostructures? (b) How can we characterize the prototypical areas into which active nanostructures may emerge? We build upon the NSF definition of active nanostructures to develop a research publication search strategy, with a particular intent to distinguish between passive and active nanotechnologies. We perform bibliometric analyses and describe the main publication trends from 1995 to 2008. We then describe the prototypes of research that emerge based on reading the abstracts and review papers encountered in our search. Preliminary results suggest that there is a sharp rise in active nanostructures publications in 2006, and this rise is maintained in 2007 and through to early 2008. We present a typology that can be used to describe the kind of active nanostructures that may be commercialized and regulated in the future.     

Is there a 2++ glueball at 1410 MeV?

A glueball component of theJ ^PC =2⁺⁺ q \(\bar q\) isoscalar states is discussed within a simple mass mixing model. As the third isoscalar necessarily present in theq \(\bar q\) ?gg mixing scheme we assumeG(1410) recently claimed by ACCMOR Collaboration in the π^? p→K _s ⁰ K _s ⁰ n data. The hypothesis is found to be compatible with the available experimental data, including two-photon decay widths and radiativeJ/ψ decays.     

Is there a glass transition in planar vortex systems?

The criteria for the existence of a glass transition in a planar vortex array with quenched disorder are studied. Applying a replica Bethe ansatz, we obtain for self-avoiding vortices the exact quenched average free energy and effective stiffness which is found to be in excellent agreement with recent numerical results for the related random bond dimer model [C. Zeng, P. L. Leath, and T. Hwa, Phys. Rev. Lett. 83, 4860 (1999)] Including a repulsive vortex interaction and a finite vortex persistence length xi, we find that for xi-->0 the system is at all temperatures in a glassy phase; a glass transition exists only for finite xi. Our results indicate that planar vortex arrays in superconducting films are glassy at presumably all temperatures.     

Is there a significant excess in bottom hadroproduction at the tevatron?

We discuss the excess in the hadroproduction of B mesons at the Tevatron. We show that an accurate use of up-to-date information on the B fragmentation function reduces the observed excess to an acceptable level. Possible implications for experimental results reporting bottom quark cross sections, also showing an excess with respect to next-to-leading order theoretical predictions, are discussed.     

Is there a universality of the helix-coil transition in protein models?

The similarity in the thermodynamic properties of two completely different theoretical models for the helix-coil transition is examined critically. The first model is an all-atomic representation for a poly-alanine chain, while the second model is a minimal helix-forming model that contains no system specifics. Key characteristics of the helix-coil transition, in particular, the effective critical exponents of these two models agree with each other, within a finite-size scaling analysis. Received 8 December 1999