355 research outputs found
A geometric approach to scalar field theories on the supersphere
Following a strictly geometric approach we construct globally supersymmetric
scalar field theories on the supersphere, defined as the quotient space
. We analyze the superspace geometry of the
supersphere, in particular deriving the invariant vielbein and spin connection
from a generalization of the left-invariant Maurer-Cartan form for Lie groups.
Using this information we proceed to construct a superscalar field action on
, which can be decomposed in terms of the component fields, yielding a
supersymmetric action on the ordinary two-sphere. We are able to derive
Lagrange equations and Noether's theorem for the superscalar field itself.Comment: 38 pages, 1 figur
Observation of Feshbach resonances between two different atomic species
We have observed three Feshbach resonances in collisions between lithium-6
and sodium-23 atoms. The resonances were identified as narrow loss features
when the magnetic field was varied. The molecular states causing these
resonances have been identified, and additional lithium-sodium resonances are
predicted. These resonances will allow the study of degenerate Bose-Fermi
mixtures with adjustable interactions, and could be used to generate ultracold
heteronuclear molecules
Formation Time of a Fermion Pair Condensate
The formation time of a condensate of fermionic atom pairs close to a
Feshbach resonance was studied. This was done using a phase-shift method in
which the delayed response of the many-body system to a modulation of the
interaction strength was recorded. The observable was the fraction of condensed
molecules in the cloud after a rapid magnetic field ramp across the Feshbach
resonance. The measured response time was slow compared to the rapid ramp,
which provides final proof that the molecular condensates reflect the presence
of fermion pair condensates before the ramp.Comment: 5 pages, 4 figure
Cerenkov radiation and scalar stars
We explore the possibility that a charged particle moving in the
gravitational field generated by a scalar star could radiate energy via a
recently proposed gravitational \v{C}erenkov mechanism. We numerically prove
that this is not possible for stable boson stars. We also show that soliton
stars could have \v{C}erenkov radiation for particular values of the boson
mass, although diluteness of the star grows and actual observational
possibility decreases for the more usually discussed boson masses. These
conclusions diminish, although do not completely rule out, the observational
possibility of actually detecting scalar stars using this mechanism, and lead
us to consider other forms, like gravitational lensing.Comment: Accepted for publication in Class. Quantum Gra
Observation of Bose-Einstein Condensation of Molecules
We have observed Bose-Einstein condensation of molecules. When a spin mixture
of fermionic Li-6 atoms was evaporatively cooled in an optical dipole trap near
a Feshbach resonance, the atomic gas was converted into Li_2 molecules. Below
600 nK, a Bose-Einstein condensate of up to 900,000 molecules was identified by
the sudden onset of a bimodal density distribution. This condensate realizes
the limit of tightly bound fermion pairs in the crossover between BCS
superfluidity and Bose-Einstein condensation.Comment: 4 pages, 3 figure
Odd-even mass differences from self-consistent mean-field theory
We survey odd-even nuclear binding energy staggering using density functional
theory with several treatments of the pairing interaction including the BCS,
Hartree-Fock-Bogoliubov, and the Hartree-Fock-Bogoliubov with the Lipkin-Nogami
approximation. We calculate the second difference of binding energies and
compare with 443 measured neutron energy differences in isotope chains and 418
measured proton energy differences in isotone chains. The particle-hole part of
the energy functional is taken as the SLy4 Skyrme parametrization and the
pairing part of the functional is based on a contact interaction with possible
density dependence. An important feature of the data, reproduced by the theory,
is the sharp gap quenching at magic numbers. With the strength of the
interaction as a free parameter, the theory can reproduce the data to an rms
accuracy of about 0.25 MeV. This is slightly better than a single-parameter
phenomenological description but slightly poorer than the usual two-parameter
phenomenological form C/A^alpha . The following conclusions can be made about
the performance of common parametrization of the pairing interaction: (i) there
is a weak preference for a surface-peaked neutron-neutron pairing, which might
be attributable to many-body effects; (ii) a larger strength is required in the
proton pairing channel than in the neutron pairing channel; (iii) pairing
strengths adjusted to the well-known spherical isotope chains are too weak to
give a good overall fit to the mass differences.Comment: 13 pages, 9 figure
Regularized Kerr-Newman Solution as a Gravitating Soliton
The charged, spinning and gravitating soliton is realized as a regular
solution of the Kerr-Newman field coupled with a chiral Higgs model. A regular
core of the solution is formed by a domain wall bubble interpolating between
the external Kerr-Newman solution and a flat superconducting interior. An
internal electromagnetic (em) field is expelled to the boundary of the bubble
by the Higgs field. The solution reveals two new peculiarities: (i) the Higgs
field is oscillating, similar to the known oscillon models, (ii) the em field
forms on the edge of the bubble a Wilson loop, resulting in quantization of the
total angular momentum.Comment: Final published version, essential corrections, title changed, 8
pages, one fi
Exact inflationary solutions
We present a new class of exact inflationary solutions for the evolution of a
universe with spatial curvature, filled with a perfect fluid, a scalar field
with potential and a cosmological
constant . With the potential and a negative cosmological
constant, the scale factor experiments a graceful exit.
We give a brief discussion about the physical meaning of the solutions.Comment: 10 pages, revtex file, 6 figures included with epsf. To be published
in IJMP-
Nuclear Tetrahedral Symmetry: Possibly Present Throughout the Periodic Table
More than half a century after the fundamental, spherical shell structure in
nuclei has been established, theoretical predictions indicate that the
shell-gaps comparable or even stronger than those at spherical shapes may
exist. Group-theoretical analysis supported by realistic mean-field
calculations indicate that the corresponding nuclei are characterized by the
('double-tetrahedral') group of symmetry, exact or approximate. The
corresponding strong shell-gap structure is markedly enhanced by the existence
of the 4-dimensional irreducible representations of the group in question and
consequently it can be seen as a geometrical effect that does not depend on a
particular realization of the mean-field. Possibilities of discovering the
corresponding symmetry in experiment are discussed.Comment: 4 pages in LaTeX and 4 figures in eps forma
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