Coexistence of different types of vortex lines in anisotropic superconductors

We considered a system of two vortex lines running in different directions with their average vortex direction making an arbitrary angle theta with respect to the crystal c axis. The free energy of this system is calculated as a function of the relative angle 2 alpha between the two inclined vortex lines with respect to each other. For sufficiently high anisotropy, it is shown that, as the induction is tilted away from the crystal c axis (theta not equal 0), the inclined vortex lines (alpha not equal 0) suddenly becomes more stable than that with parallel vortex lines (alpha = 0). While theta is increased, the system continuously changes towards the parallel configuration before the angle theta approaches 90 degrees.

A SUGGESTION ON THE PAIR OF QSO TRIPLETS 1130+106 (B,A,C), (X,Y,Z)

The alignment of a pair of QSO triplets discovered by Arp and Hazard are tentatively explained by a combination of (I) the idea of quasar ejection by galaxies; (II) a construction by Narlikar suggesting a common origin for the six images; and (III) a nontrivial topology of cosmic space.

Magnetic field of an in-plane vortex inside and outside a layered superconducting film

In the present work we study an anisotropic layered superconducting film of finite thickness. The film surfaces are considered parallel to the be face of the crystal. The vortex lines are oriented perpendicular to the film surfaces and parallel to the superconducting planes. We calculate the local field and the London free energy for this geometry. Our calculation is a generalization of previous works where the sample is taken as a semi-infinite superconductor. As an application of this theory we investigate the flux spreading at the super conducting surface.

Controlling Excitation Inversion of a Cooper Pair Box Interacting with a Nanomechanical Resonator

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Superconducting vortex fluctuations in YBa2Cu3O7-δ

Measurements of magnetization in YBa2Cu3O7-δ single crystals were performed for applied fields H parallel and perpendicular to the ab planes. The data show a temperature T = T* at which the magnetization M(T*) is independent of the applied field. This result is interpreted as due to vortex fluctuations of an anisotropic 3-D superconductor.

Interaction potential between vortex lines for uniaxial superconductors in the London approximation

Two distinct expressions of the interaction potential between arbitrarily oriented curved vortex lines with respect to the crystal c axis are derived within the London approximation. One of these expressions is used to compute the eigenvalues of the elasticity matrix. We examine the elastic properties of the vortex chain lattice, recently proposed, concerning shearing deformation.

Vortex lattice and matching fields for a long superconducting wire

We investigate the flux penetration patterns and matching fields of a long cylindrical wire of circular cross section in the presence of an external magnetic field. For this study we write the London theory for a long cylinder both for the mixed and Meissner states, with boundary conditions appropriate for this geometry. Using the Monte Carlo simulated annealing method, the free energy of the mixed state is minimized with respect to the vortex position and we obtain the ground state of the vortex lattice for N=3 up to 18 vortices. The free energy of the Meissner and mixed states provides expressions for the matching fields. We find that, as in the case of samples of different geometry, the finite-size effect provokes a delay on the vortex penetration and a vortex accumulation in the center of the sample. The vortex patterns obtained are in good agreement with experimental results.

Signals for CP violation in scalar tau pair production at muon colliders

We discuss signals for CP violation in μ + μ - → Τ̃ i - Τ̃ j +, where i, j = 1, 2 label the two scalar Τ mass eigenstates. We assume that these reactions can proceed through the production and decay of the heavy neutral Higgs bosons present in supersymmetric models. CP violation in the Higgs sector can be probed through a rate asymmetry even with unpolarized beams, while the CP-odd phase associated with the Τ̃ mass matrix can be probed only if the polarization of at least one beam can be varied. These asymmetries might be O (1).

Effective pair potentials and structure of water

Classical Monte Carlo calculations have been performed in order to investigate the ability of the TIP4P, SPC, and SPCE water models to reproduce the structural features of liquid water. The simulations were carried out in the NPT ensemble at 4 thermodynamic conditions. The results are compared with recent neutron diffraction data. Essentially, the three models capture equally well the thermodynamic and structural features of water. Although they were parametrized to reproduce the water properties at ambient conditions, the agreement with the experimental pair correlation functions was even better at supercritical conditions. This is because the effective pair potentials have some difficulty to reproduce cooperative interactions, like hydrogen bonds. These interactions are less effective at supercritical conditions, where the liquid behaves roughly like a gas.

Supersymmetric Higgs boson pair production at hadron colliders

We study the pair production of neutral Higgs bosons through gluon fusion at hadron colliders in the framework of the minimal supersymmetric standard model. We present analytical expressions for the relevant amplitudes, including both quark and squark loop contributions, and allowing for mixing between the superpartners of left- and right-handed quarks. Squark loop contributions can increase the cross section for the production of two CP-even Higgs bosons by more than two orders of magnitude, if the relevant trilinear soft breaking parameter is large and the mass of the lighter squark eigenstate is not too far above its current lower bound. In the region of large tan β, neutral Higgs boson pair production might even be observable in the 4b final state during the next run of the Fermilab Tevatron collider. ©1999 The American Physical Society.

Strong-interaction effects in stop pair production at e+e- colliders

We discuss perturbative and non-perturbative strong-interaction effects in the pair production of stop squarks (t̃1) at e+e- colliders. Events with an additional hard gluon allow to detect or exclude t̃1t̃*1 production even in scenarios with very small mass splitting between ti and an invisible lightest supersymmetric particle (LSP). Such events can also help to establish that t̃1 transforms as a triplet under SU(3)C. We also carefully study non-perturbative t̃1 fragmentation, which is currently not well understood: not only is the t̃1 fragmentation function not known very well, but also there are ambiguities in the algorithm employed to model fragmentation. We present numerical results both for CERN LEP-183 and for a proposed future e+e- collider operating at center-of-mass energy s1/2 = 500 GeV.

Bose-Einstein correlations in W-pair decays

Bose-Einstein correlations are studied in semileptonic (WW → qq̄lv) and fully hadronic (WW → qq̄qq̄) W-pair decays with the ALEPH detector at LEP at centre-of-mass energies of 172, 183 and 189 GeV. They are compared with those made at the Z peak after correction for the different flavour compositions. A Monte Carlo model of Bose-Einstein correlations based on the JETSET hadronization scheme was tuned to the Z data and reproduces the correlations in the WW → qq̄lv events. The same Monte Carlo reproduces the correlations in the WW → qq̄qq̄ channel assuming independent fragmentation of the two W's. A variant of this model with Bose-Einstein correlations between decay products of different W's is disfavoured. (C) 2000 Published by Elsevier Science B.V.

Supersymmetric Higgs boson pair production: Discovery prospects at hadron colliders

We study the potential of hadron colliders in the search for the pair production of neutral Higgs bosons in the framework of the minimal supersymmetric standard model. We perform a detailed signal and background analysis, working out efficient kinematical cuts for the extraction of the signal. The important role of squark loop contributions to the signal is re-emphasized. If the signal is sufficiently enhanced by these contributions, it could even be observable at the next run of the upgraded Tevatron collider in the near future. At the LHC the pair production of light and heavy Higgs bosons might be detectable simultaneously.

Free expansion of attractive and repulsive Bose-Einstein condensed vortex states

A numerical study of the time-dependent Gross-Pitaevskii equation for an axially symmetric trap to obtain insight into the free expansion of vortex states of BEC is presented. As such, the ratio of vortex-core radius to radia rms radius xc/xrms(<1) is found to play an interesting role in the free expansion of condensed vortex states. the larger this ratio, the more prominent is the vortex core and the easier is the possibility of experimental detection of vortex states.

Dynamics of a collapsing and exploding Bose-Einstein condensed vortex state

The dynamics of small repulsive Bose-Einstein condensed vortex states of 85Rb atoms in a cylindrical traps with low angular momentum was studied. The time-dependent mean-field Gross-Pitaevskii equation was used for the study. The condensates collapsed and atoms ejected via explosion and a remnant condensate with a smaller number of atoms emerges that survived for a long time.