173 research outputs found
A High Precision Study of the QQ(bar) Potential from Wilson Loops in the Regime of String Breaking
For lattice QCD with two sea quark flavours we compute the static quark
antiquark potential V(R) in the regime where string breaking is expected. In
order to increase statistics, we make full use of the lattice information by
including all lattice vectors R to any possible lattice separation in the
infrared regime. The corresponding paths between the lattice points are
constructed by means of a generalized Bresenham algorithm as known from
computer graphics. As a results we achieve a determination of the unquenched
potential in the range .8 to 1.5 fm with hitherto unknown precision.
Furthermore, we demonstrate some error reducing methods for the evaluation of
the transition matrix element between two- and four-quark states.Comment: 6 pages, 7 figure
Flavour singlet pseudoscalar masses in N_f = 2 QCD
We perform a lattice mass analysis in the flavour singlet pseudoscalar
channel on the SESAM and TXL full QCD vacuum configurations, with 2 active
flavours of dynamical Wilson fermions at beta = 5.6. At our inverse lattice
spacing, a^-1 = 2.3 GeV, we retrieve by a chiral extrapolation to the physical
light quark masses the value m_eta' = 3.7(+8)(-4) m_pi. A crude extrapolation
from (N_f = 3) phenomenology would suggest m_eta' \approx 5.1 m_pi for N_f = 2
QCD. we verify that the mass gap between the singlet state eta' and the pi
flavour triplt state is due to gauge configurations with non-trivial topology.Comment: 8 pages, 10 figure
An Estimate of alpha_S from Bottomonium in Unquenched QCD
We estimate the strong coupling constant from the perturbative expansion of
the plaquette. The scale is set by the 2S-1S and 1P-1S splittings in
bottomonium which are computed in NRQCD on dynamical gauge configurations with
nf=2 degenerate Wilson quarks at intermediate masses. We have increased the
statistics of our spectrum calculation in order to reliably extrapolate in the
sea-quark mass. We find a value of alpha_MS(m_Z) = 0.1118(26) which is somewhat
lower than previous estimates within NRQCD.Comment: LATTICE98(heavyqk
Optimization of Pressure Swing Adsorption via a Trust-Region Filter Algorithm and Equilibrium Theory
Decorrelating Topology with HMC
The investigation of the decorrelation efficiency of the HMC algorithm with
respect to vacuum topology is a prerequisite for trustworthy full QCD
simulations, in particular for the computation of topology sensitive
quantities. We demonstrate that for mpi/mrho ratios <= 0.69 sufficient
tunneling between the topological sectors can be achieved, for two flavours of
dynamical Wilson fermions close to the scaling region beta=5.6. Our results are
based on time series of length 5000 trajectories.Comment: change of comments: LATTICE98(confine
Structure-directing factors when introducing hydrogen bond functionality to metal?organic frameworks
The introduction of H-bond donor/acceptor functionality into metal-organic frameworks (MOFs) can have a beneficial effect on their molecular recognition, uptake selectivity and catalytic properties. The changes in ligand geometry induced by incorporation of functional groups may also affect the topology and composition of the resultant MOFs. Herein, we present a comprehensive study of functional group incorporation into MOFs, linked by either Zn2+ paddlewheel units or monomeric Zn2+ corners, which exhibit pcu and dia topology, respectively. Crystallographic analysis shows that amide groups can be easily incorporated into isoreticular pcu pillared-MOFs, whilst integration of urea units results in materials with dia topology. Molecular simulations allow the examination of hypothetical structures with differing constitutions and topologies, and highlight the influence of the urea units in generating the experimentally observed topologies. Noncovalent interactions between independent nets may be significant structure-directing influences, a finding which has great implications for the design of MOFs containing more complex functional groupsFil: Forgan, Ross S.. University Of Glasgow; Reino UnidoFil: Marshall, Ross J.. University Of Glasgow; Reino UnidoFil: Struckmann, Mona. University Of Glasgow; Reino UnidoFil: Bleine, Aurore B.. University Of Glasgow; Reino UnidoFil: Long, De Liang. University Of Glasgow; Reino UnidoFil: Bernini, Maria Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Fairen Jimenez, D.. University of Cambridge; Reino Unid
On the low fermionic eigenmode dominance in QCD on the lattice
We demonstrate the utility of a spectral approximation to fermion loop
operators using low-lying eigenmodes of the hermitian Dirac-Wilson matrix, Q.
The investigation is based on a total of 400 full QCD vacuum configurations,
with two degenerate flavors of dynamical Wilson fermions at beta =5.6, at two
different sea quark masses. The spectral approach is highly competitive for
accessing both topological charge and disconnected diagrams, on large lattices
and small quark masses. We propose suitable partial summation techniques that
provide sufficient saturation for estimating Tr Q^{-1}, which is related to the
topological charge. In the effective mass plot of the eta' meson we achieved a
consistent early plateau formation, by ground state projecting the connected
piece of its propagator.Comment: 15 pages, 25 figures, citations adde
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