357 research outputs found
Spin textures in condensates with large dipole moments
We have solved numerically the ground states of a Bose-Einstein condensate in
the presence of dipolar interparticle forces using a semiclassical approach.
Our motivation is to model, in particular, the spontaneous spin textures
emerging in quantum gases with large dipole moments, such as 52Cr or Dy
condensates, or ultracold gases consisting of polar molecules. For a
pancake-shaped harmonic (optical) potential, we present the ground state phase
diagram spanned by the strength of the nonlinear coupling and dipolar
interactions. In an elongated harmonic potential, we observe a novel helical
spin texture. The textures calculated according to the semiclassical model in
the absence of external polarizing fields are predominantly analogous to
previously reported results for a ferromagnetic F = 1 spinor Bose-Einstein
condensate, suggesting that the spin textures arising from the dipolar forces
are largely independent of the value of the quantum number F or the origin of
the dipolar interactions.Comment: 9 pages, 6 figure
Renormalisation of quark bilinears with Nf=2 Wilson fermions and tree-level improved gauge action
We present results for the renormalisation constants of bilinear quark
operators, using the Nf=2 twisted mass Wilson action at maximal twist (which
guarantees automatic O(a) improvement) and the tree-level Symanzik improved
gauge action. The scale-independent renormalisation constants are computed with
a new method, which makes use of both standard twisted mass and
Osterwalder-Seiler fermions. Moreover, the results from an RI-MOM calculation
are presented for both scale independent and scale dependent renormalisation
constants.Comment: 7 pages, talk at The XXV International Symposium on Lattice Field
Theory, July 30 - August 4 2007, Regensbur
Stable Fractional Vortices in the Cyclic States of Bose-Einstein Condensates
We propose methods to create fractional vortices in the cyclic state of an F
= 2 spinor Bose-Einstein condensate by manipulating its internal spin structure
using pulsed microwave and laser fields. The stability of such vortices is
studied as a function of the rotation frequency of the confining harmonic trap
both in pancake and cigar shaped condensates. We find a range of parameters for
which the so-called 1/3-vortex state is energetically favorable. Such
fractional vortices could be created in condensates of 87Rb atoms using current
experimental techniques facilitating probing of topological defects with
non-Abelian statistics.Comment: 5 pages, 2 figure
Angular momentum exchange between coherent light and matter fields
Full, three dimensional, time-dependent simulations are presented
demonstrating the quantized transfer of angular momentum to a Bose-Einstein
condensate from a laser carrying orbital angular momentum in a
Laguerre-Gaussian mode. The process is described in terms of coherent Bragg
scattering of atoms from a chiral optical lattice. The transfer efficiency and
the angular momentum content of the output coupled vortex state are analyzed
and compared with a recent experiment.Comment: 4 pages, 4 figure
Giant Vortex Lattice Deformations in Rapidly Rotating Bose-Einstein Condensates
We have performed numerical simulations of giant vortex structures in rapidly
rotating Bose-Einstein condensates within the Gross-Pitaevskii formalism. We
reproduce the qualitative features, such as oscillation of the giant vortex
core area, formation of toroidal density hole, and the precession of giant
vortices, observed in the recent experiment [Engels \emph{et.al.}, Phys. Rev.
Lett. {\bf 90}, 170405 (2003)]. We provide a mechanism which quantitatively
explains the observed core oscillation phenomenon. We demonstrate the clear
distinction between the mechanism of atom removal and a repulsive pinning
potential in creating giant vortices. In addition, we have been able to
simulate the transverse Tkachenko vortex lattice vibrations.Comment: 5 pages, 6 figures; revised description of core oscillation, new
subfigur
Virtual meson cloud of the nucleon and generalized parton distributions
We present the general formalism required to derive generalized parton
distributions within a convolution model where the bare nucleon is dressed by
its virtual meson cloud. In the one-meson approximation the Fock states of the
physical nucleon are expanded in a series involving a bare nucleon and
two-particle, meson-baryon, states. The baryon is assumed here to be either a
nucleon or a described within the constituent quark model in terms of
three valence quarks; correspondingly, the meson, assumed to be a pion, is
described as a quark-antiquark pair. Explicit expressions for the unpolarized
generalized parton distributions are obtained and evaluated in different
kinematics.Comment: 37 pages, 9 figures, minor corrections, and figure 3 replaced;
version to appear in Phys. Rev.
Improved Semileptonic Form Factor Calculations in Lattice QCD
We investigate the computational efficiency of two stochastic based
alternatives to the Sequential Propagator Method used in Lattice QCD
calculations of heavy-light semileptonic form factors. In the first method, we
replace the sequential propagator, which couples the calculation of two of the
three propagators required for the calculation, with a stochastic propagator so
that the calculations of all three propagators are independent. This method is
more flexible than the Sequential Propagator Method but introduces stochastic
noise. We study the noise to determine when this method becomes competitive
with the Sequential Propagator Method, and find that for any practical
calculation it is competitive with or superior to the Sequential Propagator
Method. We also examine a second stochastic method, the so-called ``one-end
trick", concluding it is relatively inefficient in this context. The
investigation is carried out on two gauge field ensembles, using the
non-perturbatively improved Wilson-Sheikholeslami-Wohlert action with N_f=2
mass-degenerate sea quarks. The two ensembles have similar lattice spacings but
different sea quark masses. We use the first stochastic method to extract
-improved, matched lattice results for the semileptonic form
factors on the ensemble with lighter sea quarks, extracting f_+(0)
Mass of the b-quark and B-decay constants from Nf=2+1+1 twisted-mass Lattice QCD
We present precise lattice computations for the b-quark mass, the quark mass
ratios mb/mc and mb/ms as well as the leptonic B-decay constants. We employ
gauge configurations with four dynamical quark flavors, up/down, strange and
charm, at three values of the lattice spacing (a ~ 0.06 - 0.09 fm) and for pion
masses as low as 210 MeV. Interpolation in the heavy quark mass to the bottom
quark point is performed using ratios of physical quantities computed at nearby
quark masses exploiting the fact that these ratios are exactly known in the
static quark mass limit. Our results are also extrapolated to the physical pion
mass and to the continuum limit and read: mb(MSbar, mb) = 4.26(10) GeV, mb/mc =
4.42(8), mb/ms = 51.4(1.4), fBs = 229(5) MeV, fB = 193(6) MeV, fBs/fB =
1.184(25) and (fBs/fB)/(fK/fpi) = 0.997(17).Comment: Version to appear in PRD. Added comments to simulation setup and
error budget discussion. 1+20 pages, 9 figure
- …