9,125,905 research outputs found
Anderson localization of elementary excitations in a one dimensional Bose-Einstein condensate
We study the elementary excitations of a transversely confined Bose-Einstein
condensate in presence of a weak axial random potential. We determine the
localization length (i) in the hydrodynamical low energy regime, for a domain
of linear densities ranging from the Tonks-Girardeau to the transverse
Thomas-Fermi regime, in the case of a white noise potential and (ii) for all
the range of energies, in the ``one-dimensional mean field regime'', in the
case where the randomness is induced by a series of randomly placed point-like
impurities. We discuss our results in view of recent experiments in elongated
BEC systems.Comment: 11 pages, 6 figures. Final printed versio
Emergence of superfluid transport in a dynamical system of ultracold atoms
The dynamics of a Bose-Einstein condensate is studied theoretically in a
combined periodic plus harmonic external potential. Different dynamical regimes
of stable and unstable collective dipole and Bloch oscillations are analysed in
terms of a quantum mechanical pendulum model. Nonlinear interactions are shown
to counteract quantum-mechanical dephasing and lead to phase-coherent,
superfluid transport
Coupled atomic-molecular condensates in a double-well potential: decaying molecular oscillations
We present a four-mode model that describes coherent photo-association (PA)
in a double-well Bose-Einstein condensate, focusing on the molecular
populations in certain parameters. Our numerical results predict an interesting
strong-damping effect of molecular oscillations by controlling the particle
tunnellings and PA light strength, which may provide a promising way for
creating a stable molecular condensate via coherent PA in a magnetic
double-well potential.Comment: 6 pages, 4 figures, submitte
Nuclear recoil effect on the magnetic-dipole decay rates of atomic levels
The effect of finite nuclear mass on the magnetic-dipole transition
probabilities between fine-structure levels of the same term is investigated.
Based on a rigorous QED approach a nonrelativistic formula for the recoil
correction to first order in m_e/M is derived. Numerical results for
transitions of experimental interest are presented.Comment: 9 page
Ground State Properties of an Asymmetric Hubbard Model for Unbalanced Ultracold Fermionic Quantum Gases
In order to describe unbalanced ultracold fermionic quantum gases on optical
lattices in a harmonic trap, we investigate an attractive () asymmetric
() Hubbard model with a Zeeman-like magnetic
field. In view of the model's spatial inhomogeneity, we focus in this paper on
the solution at Hartree-Fock level. The Hartree-Fock Hamiltonian is
diagonalized with particular emphasis on superfluid phases. For the special
case of spin-independent hopping we analytically determine the number of
solutions of the resulting self-consistency equations and the nature of the
possible ground states at weak coupling. Numerical results for unbalanced
Fermi-mixtures are presented within the local density approximation. In
particular, we find a fascinating shell structure, involving normal and
superfluid phases. For the general case of spin-dependent hopping we calculate
the density of states and the possible superfluid phases in the ground state.
In particular, we find a new magnetized superfluid phase.Comment: 9 pages, 5 figure
Generic theory of active polar gels: a paradigm for cytoskeletal dynamics
We develop a general theory for active viscoelastic materials made of polar
filaments. This theory is motivated by the dynamics of the cytoskeleton. The
continuous consumption of a fuel generates a non equilibrium state
characterized by the generation of flows and stresses. Our theory can be
applied to experiments in which cytoskeletal patterns are set in motion by
active processes such as those which are at work in cells.Comment: 28 pages, 2 figure
Measurement of the LT-asymmetry in \pi^0 electroproduction at the energy of the \Delta (1232) resonance
The reaction p(e,e'p)pi^0 has been studied at Q^2=0.2 (GeV/c)^2 in the region
of W=1232 MeV. From measurements left and right of q, cross section asymmetries
\rho_LT have been obtained in forward kinematics \rho_LT(\theta_\pi^0=20deg) =
(-11.68 +/- 2.36_stat +/- 2.36_sys)$ and backward kinematics
\rho_LT(\theta_\pi^0=160deg) =(12.18 +/- 0.27_stat +/- 0.82_sys). Multipole
ratios \Re(S_1+^* M_1+)/|M_1+|^2 and \Re(S_0+^* M_1+)/|M_1+|^2 were determined
in the framework of the MAID2003 model. The results are in agreement with older
data. The unusally strong negative \Re(S_0+^* M_1+)/|M_1+|^2 required to bring
also the result of Kalleicher et al. in accordance with the rest of the data is
almost excluded.Comment: 7 pages, 7 figures, 4 tables. Changed content. Accepted for
publication in EPJ
Coulomb parameters and photoemission for the molecular metal TTF-TCNQ
We employ density-functional theory to calculate realistic parameters for an
extended Hubbard model of the molecular metal TTF-TCNQ. Considering both intra-
and intermolecular screening in the crystal, we find significant longer-range
Coulomb interactions along the molecular stacks, as well as inter-stack
coupling. We show that the long-range Coulomb term of the extended Hubbard
model leads to a broadening of the spectral density, likely resolving the
problems with the interpretation of photoemission experiments using a simple
Hubbard model only.Comment: 4 pages, 2 figure
Strange particle production in proton-proton collisions at TeV with ALICE at the LHC
The production of mesons containing strange quarks (K, ) and both
singly and doubly strange baryons (, Anti-, and
+Anti-) are measured at central rapidity in pp collisions at
= 0.9 TeV with the ALICE experiment at the LHC. The results are
obtained from the analysis of about 250 k minimum bias events recorded in 2009.
Measurements of yields (dN/dy) and transverse momentum spectra at central
rapidities for inelastic pp collisions are presented. For mesons, we report
yields () of 0.184 0.002 stat. 0.006 syst. for K and
0.021 0.004 stat. 0.003 syst. for . For baryons, we find
= 0.048 0.001 stat. 0.004 syst. for , 0.047
0.002 stat. 0.005 syst. for Anti- and 0.0101 0.0020 stat.
0.0009 syst. for +Anti-. The results are also compared with
predictions for identified particle spectra from QCD-inspired models and
provide a baseline for comparisons with both future pp measurements at higher
energies and heavy-ion collisions.Comment: 33 pages, 21 captioned figures, 10 tables, authors from page 28,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/387
Structures of the , mesons and the strong coupling constants , with the light-cone QCD sum rules
In this article, with the assumption of explicit isospin violation arising
from the mixing, we take the point of view that the scalar
mesons and have both strange and non-strange
quark-antiquark components and evaluate the strong coupling constants and within the framework of the light-cone QCD sum
rules approach. The large strong scalar- couplings through both the
and components ,
,
and will support the
hadronic dressing mechanism, furthermore, in spite of the constituent structure
differences between the and mesons, the strange
components have larger strong coupling constants with the state than
the corresponding non-strange ones, and . From the existing controversial values,
we can not reach a general consensus on the strong coupling constants , and the mixing angles.Comment: 14 pages; Revised versio
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