5,350 research outputs found
Phonon instability in two-dimensional dipolar Bose-Einstein Condensates
The partially attractive character of the dipole-dipole interaction leads to
phonon instability in dipolar condensates, which is followed by collapse in
three-dimensional geometries. We show that the nature of this instability is
fundamentally different in two-dimensional condensates, due to the
dipole-induced stabilization of two-dimensional bright solitons. As a
consequence, a transient gas of attractive solitons is formed, and collapse may
be avoided. In the presence of an harmonic confinement, the instability leads
to transient pattern formation followed by the creation of stable
two-dimensional solitons. This dynamics should be observable in on-going
experiments, allowing for the creation of stable two-dimensional solitons for
the first time ever in quantum gases.Comment: 4 pages, 4 figure
Faraday patterns in dipolar Bose-Einstein condensates
Faraday patterns can be induced in Bose-Einstein condensates by a periodic
modulation of the system nonlinearity. We show that these patterns are
remarkably different in dipolar gases with a roton-maxon excitation spectrum.
Whereas for non-dipolar gases the pattern size decreases monotonously with the
driving frequency, patterns in dipolar gases present, even for shallow roton
minima, a highly non trivial frequency dependence characterized by abrupt
pattern size transitions, which are especially pronounced when the dipolar
interaction is modulated. Faraday patterns constitute hence an optimal tool for
revealing the onset of the roton minimum, a major key feature of dipolar gases.Comment: 4 pages, 10 figure
Kelvon-roton instability of vortex lines in dipolar Bose-Einstein condensates
The physics of vortex lines in dipolar condensates is studied. Due to the
nonlocality of the dipolar interaction, the 3D character of the vortex plays a
more important role in dipolar gases than in typical short-range interacting
ones. In particular, the dipolar interaction significantly affects the
stability of the transverse modes of the vortex line. Remarkably, in the
presence of a periodic potential along the vortex line, a roton minimum may
develop in the spectrum of transverse modes. We discuss the appropriate
conditions at which this roton minimum may eventually lead to an instability of
the straight vortex line, opening new scenarios for vortices in dipolar gases.Comment: 4 pages, 3 eps figure
The Role of in Two-pion Exchange Three-nucleon Potential
In this paper we have studied the two-pion exchange three-nucleon potential
using an approximate chiral symmetry of the
strong interaction. The off-shell pion-nucleon scattering amplitudes obtained
from the Weinberg Lagangian are supplemented with contributions from the
well-known -term and the exchange. It is the role of the
-resonance in , which we have investigated in detail in the
framework of the Lagrangian field theory. The -contribution is quite
appreciable and, more significantly, it is dependent on a parameter Z which is
arbitrary but has the empirical bounds . We find that the
-contribution to the important parameters of the depends
on the choice of a value for Z, although the correction to the binding energy
of triton is not expected to be very sensitive to the variation of Z within its
bounds.Comment: 14 pages, LaTe
Three-dimensional Roton-Excitations and Supersolid formation in Rydberg-excited Bose-Einstein Condensates
We study the behavior of a Bose-Einstein condensate in which atoms are weakly
coupled to a highly excited Rydberg state. Since the latter have very strong
van der Waals interactions, this coupling induces effective, nonlocal
interactions between the dressed ground state atoms, which, opposed to dipolar
interactions, are isotropically repulsive. Yet, one finds partial attraction in
momentum space, giving rise to a roton-maxon excitation spectrum and a
transition to a supersolid state in three-dimensional condensates. A detailed
analysis of decoherence and loss mechanisms suggests that these phenomena are
observable with current experimental capabilities.Comment: 4 pages, 5 figure
Testing Supergravity Grand Unification at Future Accelerator and Underground Experiments
The full parameter space of supergravity grand unified theory with
type proton decay is analysed using renormalization
group induced electroweak symmetry breaking under the restrictions that the
universal scalar mass and gluino mass are TeV (no extreme fine
tuning) and the Higgs triplet mass obeys . Future proton
decay experiments at SuperKamiokande or ICARUS can reach a sensitivity for the
mode of yr allowing a number of
predictions concerning the SUSY mass spectrum. Thus either the decay mode will be seen at these experiments or a
chargino of mass GeV will exist and hence be observable
at LEP2. Further, if yr,
then either the light Higgs has mass GeV or GeV i.e. either the light Higgs or the light chargino (or both) would be
observable at LEP2. Thus, the combination of future accelerator and future
underground experiments allow for strong experimental tests of this theory.Comment: 7 figures available upon request, CTP-TAMU-32/93, NUB-TH-3066/93 and
SSCL-Preprint-44
Detecting Physics At The Post-GUT And String Scales By Linear Colliders
The ability of linear colliders to test physics at the post-GUT scale is
investigated. Using current estimates of measurements available at such
accelerators, it is seen that soft breaking masses can be measured with errors
of about (1-20)%. Three classes of models in the post-GUT region are examined:
models with universal soft breaking masses at the string scale, models with
horizontal symmetry, and string models with Calabi-Yau compactifications. In
each case, linear colliders would be able to test directly theoretical
assumptions made at energies beyond the GUT scale to a good accuracy,
distinguish between different models, and measure parameters that are expected
to be predictions of string models.Comment: Latex, 21 pages, no figure
Collinear order in a frustrated three-dimensional spin- antiferromagnet LiCuWO
Magnetic frustration in three dimensions (3D) manifests itself in the
spin- insulator LiCuWO. Density-functional band-structure
calculations reveal a peculiar spin lattice built of triangular planes with
frustrated interplane couplings. The saturation field of 29 T contrasts with
the susceptibility maximum at 8.5 K and a relatively low N\'eel temperature
K. Magnetic order below is collinear with the propagation
vector and an ordered moment of 0.65(4) according to
neutron diffraction data. This reduced ordered moment together with the low
maximum of the magnetic specific heat () pinpoint strong
magnetic frustration in 3D. Collinear magnetic order suggests that quantum
fluctuations play crucial role in this system, where a non-collinear spiral
state would be stabilized classically.Comment: published version with supplemental material merged into the tex
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