1,073 research outputs found
Can lattice data for two heavy-light mesons be understood in terms of simply two-quark potentials?
By comparing lattice data for the two heavy-light meson system (Q^2 qbar^2)
with a standard many-body approach employing only interquark potentials, it is
shown that the use of unmodified two-quark potentials leads to a gross
overestimate of the binding energy.Comment: Contribution to LATTICE99 (Heavy Quarks). 3 pages, 2 ps figure
The radial distributions of a heavy-light meson on a lattice
In an earlier work, the charge (vector) and matter (scalar) radial
distributions of heavy-light mesons were measured in the quenched approximation
on a 16^3 times 24 lattice with a quark-gluon coupling of 5.7, a lattice
spacing of 0.17 fm, and a hopping parameter corresponding to a light quark mass
about that of the strange quark.
Several improvements are now made: 1) The configurations are generated using
dynamical fermions with a quark-gluon coupling of 5.2 (a lattice spacing of
0.14 fm); 2) Many more gauge configurations are included (78 compared with the
earlier 20); 3) The distributions at many off-axis, in addition to on-axis,
points are measured; 4) The data-analysis is much more complete. In particular,
distributions involving excited states are extracted.
The exponential decay of the charge and matter distributions can be described
by mesons of mass 0.9+-0.1 and 1.5+-0.1 GeV respectively - values that are
consistent with those of vector and scalar qqbar-states calculated directly
with the same lattice parameters.Comment: 3 pages, 4 figures, Lattice2002(heavyquark
Conditions for waveguide decoupling in square-lattice photonic crystals
We study coupling and decoupling of parallel waveguides in two-dimensional
square-lattice photonic crystals. We show that the waveguide coupling is
prohibited at some wavelengths when there is an odd number of rows between the
waveguides. In contrast, decoupling does not take place when there is even
number of rows between the waveguides. Decoupling can be used to avoid cross
talk between adjacent waveguides.Comment: 6 pages, 2 figure
The Charge and Matter radial distributions of Heavy-Light mesons calculated on a lattice
For a heavy-light meson with a static heavy quark, we can explore the light
quark distribution. The charge and matter radial distributions of these
heavy-light mesons are measured on a 16^3 * 24 lattice at beta=5.7 and a
hopping parameter corresponding to a light quark mass about that of the strange
quark. Both distributions can be well fitted up to 4 lattice spacings (r approx
0.7 fm) with the exponential form w_i^2(r), where w_i(r)=A exp(-r/r_i). For the
charge(c) and matter(m) distributions r_c approx 0.32(2) fm and r_m approx
0.24(2) fm. We also discuss the normalisation of the total charge and matter
integrated over all space, finding 1.30(5) and 0.4(1) respectively.Comment: 31 pages including 7 ps figure
Noise correlations of the ultra-cold Fermi gas in an optical lattice
In this paper we study the density noise correlations of the two component
Fermi gas in optical lattices. Three different type of phases, the BCS-state
(Bardeen, Cooper, and Schieffer), the FFLO-state (Fulde, Ferrel, Larkin, and
Ovchinnikov), and BP (breach pair) state, are considered. We show how these
states differ in their noise correlations. The noise correlations are
calculated not only at zero temperature, but also at non-zero temperatures
paying particular attention to how much the finite temperature effects might
complicate the detection of different phases. Since one-dimensional systems
have been shown to be very promising candidates to observe FFLO states, we
apply our results also to the computation of correlation signals in a
one-dimensional lattice. We find that the density noise correlations reveal
important information about the structure of the underlying order parameter as
well as about the quasiparticle dispersions.Comment: 25 pages, 11 figures. Some figures are updated and text has been
modifie
Fermi condensates for dynamic imaging of electro-magnetic fields
Ultracold gases provide micrometer size atomic samples whose sensitivity to
external fields may be exploited in sensor applications. Bose-Einstein
condensates of atomic gases have been demonstrated to perform excellently as
magnetic field sensors \cite{Wildermuth2005a} in atom chip
\cite{Folman2002a,Fortagh2007a} experiments. As such, they offer a combination
of resolution and sensitivity presently unattainable by other methods
\cite{Wildermuth2006a}. Here we propose that condensates of Fermionic atoms can
be used for non-invasive sensing of time-dependent and static magnetic and
electric fields, by utilizing the tunable energy gap in the excitation spectrum
as a frequency filter. Perturbations of the gas by the field create both
collective excitations and quasiparticles. Excitation of quasiparticles
requires the frequency of the perturbation to exceed the energy gap. Thus, by
tuning the gap, the frequencies of the field may be selectively monitored from
the amount of quasiparticles which is measurable for instance by
RF-spectroscopy. We analyse the proposed method by calculating the
density-density susceptibility, i.e. the dynamic structure factor, of the gas.
We discuss the sensitivity and spatial resolution of the method which may, with
advanced techniques for quasiparticle observation \cite{Schirotzek2008a}, be in
the half a micron scale.Comment: 10 pages, 4 figure
Finite temperature phase diagram of a polarized Fermi gas in an optical lattice
We present phase diagrams for a polarized Fermi gas in an optical lattice as
a function of temperature, polarization, and lattice filling factor. We
consider the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO), Sarma or breached pair
(BP), and BCS phases, and the normal state and phase separation. We show that
the FFLO phase appears in a considerable portion of the phase diagram. The
diagrams have two critical points of different nature. We show how various
phases leave clear signatures to momentum distributions of the atoms which can
be observed after time of flight expansion.Comment: Journal versio
The size of the pion from full lattice QCD with physical u, d, s and c quarks
We present the first calculation of the electromagnetic form factor of the π meson at physical light
quark masses. We use configurations generated by the MILC collaboration including the effect of u, d, s and c sea quarks with the Highly Improved Staggered Quark formalism. We work at three values of the lattice spacing on large volumes and with u/d quark masses going down to the physical value. We study scalar and vector form factors for a range in space-like q2 from 0.0 to -0.13 GeV2 and from their shape we extract mean square radii. Our vector form factor agrees well with experiment and we find hr2iV = 0:403(18)(6) fm2. For the scalar form factor we include quark-line disconnected
contributions which have a significant impact on the radius. We give the first results for SU(3) flavour-singlet and octet scalar mean square radii, obtaining: hr2isinglet
S = 0:506(38)(53)fm2 and hr2ioctet S = 0:431(38)(46)fm2. We discuss the comparison with expectations from chiral perturbation theory
- …