31,355 research outputs found
Ferromagnetic 0-pi Junctions as Classical Spins
The ground state of highly damped PdNi based 0-pi ferromagnetic Josephson
junctions shows a spontaneous half quantum vortex, sustained by a supercurrent
of undetermined sign. This supercurrent flows in the electrode of a Josephson
junction used as a detector and produces a phi(0)/4 shift in its magnetic
diffraction pattern. We have measured the statistics of the positive or
negative sign shift occurring at the superconducting transition of such a
junction. The randomness of the shift sign, the reproducibility of its
magnitude and the possibility of achieving exact flux compensation upon field
cooling: all these features show that 0-pi junctions behave as classical spins,
just as magnetic nanoparticles with uniaxial anisotropy.Comment: 4 pages, 4 figure
Spinor Dynamics in an Antiferromagnetic Spin-1 Condensate
We observe coherent spin oscillations in an antiferromagnetic spin-1
Bose-Einstein condensate of sodium. The variation of the spin oscillations with
magnetic field shows a clear signature of nonlinearity, in agreement with
theory, which also predicts anharmonic oscillations near a critical magnetic
field. Measurements of the magnetic phase diagram agree with predictions made
in the approximation of a single spatial mode. The oscillation period yields
the best measurement to date of the sodium spin-dependent interaction
coefficient, determining that the difference between the sodium spin-dependent
s-wave scattering lengths is Bohr radii.Comment: 5 pages, 2 figures. Changes: added reference, minor correction
A study of the Higgs and confining phases in Euclidean SU(2) Yang-Mills theories in 3d by taking into account the Gribov horizon
We study SU(2) three-dimensional Yang-Mills theories in presence of Higgs
fields in the light of the Gribov phenomenon. By restricting the domain of
integration in the functional integral to the first Gribov horizon, we are able
to discuss a kind of transition between the Higgs and the confining phase in a
semi-classical approximation. Both adjoint and fundamental representation for
the Higgs field are considered, leading to a different phase structure.Comment: 12 pages. Version accepted for publication in the EPJ
A remark on the BRST symmetry in the Gribov-Zwanziger theory
We show that the soft breaking of the BRST symmetry arising in the
Gribov-Zwanziger theory can be converted into a linear breaking upon
introduction of a set of BRST quartets of auxiliary fields. Due to its
compatibility with the Quantum Action Principle, the linearly broken BRST
symmetry can be directly converted into a suitable set of useful Slavnov-Taylor
identities. As a consequence, it turns out that the renormalization aspects of
the Gribov-Zwanziger theory can be addressed by means of the cohomology of a
nilpotent local operatorComment: 11 pages, final version to appear in Phys. Rev.
Pair Plasma Dominance in the Parsec-Scale Relativistic Jet of 3C345
We investigate whether a pc-scale jet of 3C345 is dominated by a normal
plasma or an electron-positron plasma. We present a general condition that a
jet component becomes optically thick for synchrotron self-absorption, by
extending the method originally developed by Reynolds et al. The general
condition gives a lower limit of the electron number density, with the aid of
the surface brightness condition, which enables us to compute the magnetic
field density. Comparing the lower limit with another independent constraint
for the electron density that is deduced from the kinetic luminosity, we can
distinguish the matter content. We apply the procedure to the five components
of 3C345 (C2, C3, C4, C5, and C7) of which angular diameters and radio fluxes
at the peak frequencies were obtainable from literature. Evaluating the
representative values of Doppler beaming factors by their equipartition values,
we find that all the five components are likely dominated by an
electron-positron plasma. The conclusion does not depend on the lower cutoff
energy of the power-law distribution of radiating particles.Comment: 17 page
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