6,721 research outputs found
Universal low-energy properties of three two-dimensional particles
Universal low-energy properties are studied for three identical bosons
confined in two dimensions. The short-range pair-wise interaction in the
low-energy limit is described by means of the boundary condition model. The
wave function is expanded in a set of eigenfunctions on the hypersphere and the
system of hyper-radial equations is used to obtain analytical and numerical
results. Within the framework of this method, exact analytical expressions are
derived for the eigenpotentials and the coupling terms of hyper-radial
equations. The derivation of the coupling terms is generally applicable to a
variety of three-body problems provided the interaction is described by the
boundary condition model. The asymptotic form of the total wave function at a
small and a large hyper-radius is studied and the universal logarithmic
dependence in the vicinity of the triple-collision point is
derived. Precise three-body binding energies and the scattering length
are calculated.Comment: 30 pages with 13 figure
Evolution and global collapse of trapped Bose condensates under variations of the scattering length
We develop the idea of selectively manipulating the condensate in a trapped
Bose-condensed gas, without perturbing the thermal cloud. The idea is based on
the possibility to modify the mean field interaction between atoms (scattering
length) by nearly resonant incident light or by spatially uniform change of the
trapping magnetic field. For the gas in the Thomas-Fermi regime we find
analytical scaling solutions for the condensate wavefunction evolving under
arbitrary variations of the scattering length . The change of from
positive to negative induces a global collapse of the condensate, and the final
stages of the collapse will be governed by intrinsic decay processes.Comment: 4 pages, LaTeX, other comments are at
http://WWW.amolf.nl/departments/quantumgassen/TITLE.HTM
What makes a crystal supersolid ?
For nearly half a century the supersolid phase of matter has remained
mysterious, not only eluding experimental observation, but also generating a
great deal of controversy among theorists. Recent discovery of what is
interpreted as a non-classical moment of inertia at low temperature in solid
He-4 has elicited much excitement as a possible first observation of a
supersolid phase. In the two years following the discovery, however, more
puzzles than answers have been provided to the fundamental issue of whether the
supersolid phase exists, in helium or any other naturally occurring condensed
matter system. Presently, there is no established theoretical framework to
understand the body of experimental data on He-4. Different microscopic
mechanisms that have been suggested to underlie superfluidity in a perfect
quantum crystal do not seem viable for \he4, for which a wealth of experimental
and theoretical evidence points to an insulating crystalline ground state. This
perspective addresses some of the outstanding problems with the interpretation
of recent experimental observations of the apparent superfluid response in He-4
(seen now by several groups) and discusses various scenarios alternative to the
homogeneous supersolid phase, such as superfluidity induced by extended defects
of the crystalline structure which include grain boundaries, dislocations,
anisotropic stresses, etc. Can a metastable superfluid "glassy" phase exist,
and can it be relevant to some of the experimental observations ? One of the
most interesting and unsolved fundamental questions is what interatomic
potentials, given the freedom to design one, can support an ideal supersolid
phase in continuous space, and can they be found in Nature.Comment: Perspective to appear in Advances in Physics, 25 pages, 7 figure
Cold Collision Frequency Shift in Two-Dimensional Atomic Hydrogen
We report a measurement of the cold collision frequency shift in atomic
hydrogen gas adsorbed on the surface of superfluid 4He at T<=90 mK. Using
two-photon electron and nuclear magnetic resonance in 4.6 T field we separate
the resonance line shifts due to the dipolar and exchange interactions, both
proportional to surface density sigma. We find the clock shift Delta v_c =
-1.0(1)x10^-7 Hz cm^-2 x sigma, which is about 100 times smaller than the value
predicted by the mean field theory and known scattering lengths in the 3D case.Comment: 4 pages, 3 figure
Unconventional superfluidity of fermions in Bose-Fermi mixtures
We examine two dimensional mixture of single-component fermions and dipolar
bosons. We calculate the self-enregies of the fermions in the normal state and
the Cooper pair channel by including first order vertex correction to derive a
modified Eliashberg equation. We predict appearance of superfluids with various
non-standard pairing symmetries at experimentally feasible transition
temperatures within the strong-coupling limit of the Eliashberg equation.
Excitations in these superfluids are anyonic and follow non-Abelian statistics
Hydrodynamic flow of expanding Bose-Einstein condensates
We study expansion of quasi-one-dimensional Bose-Einstein condensate (BEC)
after switching off the confining harmonic potential. Exact solution of
dynamical equations is obtained in framework of the hydrodynamic approximation
and it is compared with the direct numerical simulation of the full problem
showing excellent agreement at realistic values of physical parameters. We
analyze the maximum of the current density and estimate the velocity of
expansion. The results of the 1D analysis provides also qualitative
understanding of some properties of BEC expansion observed in experiments.Comment: 5 pages, 3 figures, RevTeX4. To appear in Physical Review
b --> s g g decay in the two and three Higgs doublet models with CP violating effects
We study the decay width and CP-asymmetry of the inclusive process b--> s g g
(g denotes gluon) in the three and two Higgs doublet models with complex Yukawa
couplings. We analyse the dependencies of the differential decay width and
CP-asymmetry to the s- quark energy E_s and CP violating parameter \theta. We
observe that there exist a considerable enhancement in the decay width and CP
asymmetry is at the order of 10^{-2}. Further, it is possible to predict the
sign of C_7^{eff} using the CP asymmetry.Comment: 15 pages, 7 Figures (required epsf style
Existence of two-channel Kondo regime for tunneling impurities with resonant scattering
Dynamical tunneling systems have been proposed earlier to display a
two-channel Kondo effect, the orbital index of the particle playing the role of
a pseudospin in the equivalent Kondo problem, and the spin being a silent
channel index. However, as shown recently by Aleiner et al. [Phys. Rev. Lett.
86, 2629 (2001)], the predicted two-channel Kondo behavior can never be
observed in the weak coupling regime, where the tunneling induced splitting of
the levels of the tunneling system always dominates the physics. Here we show
that the above scenario changes completely if the conduction electrons are
scattered by resonant scattering off the tunneling impurity; Then - as a
non-perturbative analysis reveals - the two-channel Kondo regime can easily be
reached.Comment: 10 PRB page
CP Violation in SUSY
Supersymmetry exhibts new sources of CP violation. We discuss the
implications of these new contributions to CP violation both in the K and B
physics. We show that CP violation puts severe constraints on low energy SUSY,
but it represents also a promising ground to look for signals of new physics.Comment: 10 pages, 2 figures. Invited talk by A. Masiero at Ferrara 2000, CP
violation physic
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