1,585 research outputs found
Molecular simulation study of the heat capacity of metastable water between 100K and 300K
Molecular simulation study of the heat capacity of metastable water between
100K and 300K Molecular simulations have been used to study the heat capacity
of metastable liquid water at low temperature adsorbed on a smooth surface.
These calculations aim at modelling water properties measured by experiments
performed on water films adsorbed on Vycor nanoporous silica at low
temperature. In particular, the study focuses on the non-monotonous variation
of the heat capacity around between 100 and 300 K
Investigations of hadron structure on the lattice
Lattice simulations of hadronic structure are now reaching a level where they
are able to not only complement, but also provide guidance to current and
forthcoming experimental programmes at, e.g. Jefferson Lab, COMPASS/CERN and
FAIR/GSI. In this talk I review the progress that has been made in this
exciting area in the past year and discuss the advances that we can expect to
see in the coming year.Topics to be covered include form factors (including
transition form factors), moments of ordinary parton and generalised parton
distribution functions, moments of distribution amplitudes, and magnetic and
electric polarisabilities. I will also highlight the progress being made in
determining disconnected contributions to hadronic properties. Of particular
interest here is the size of the contribution to various nucleonic properties
coming from strange quarks.Comment: 26 pages, 22 figures, talk presented at the XXVI International
Symposium on Lattice Field Theory, July 14-19, 2008, Williamsburg, Virginia,
US
Precision electromagnetic structure of decuplet baryons in the chiral regime
The electromagnetic properties of the baryon decuplet are calculated in
quenched QCD on a 20^3 x 40 lattice with a lattice spacing of 0.128 fm using
the fat-link irrelevant clover (FLIC) fermion action with quark masses
providing a pion mass as low as 300 MeV. Magnetic moments and charge radii are
extracted from the electric and magnetic form factors for each individual quark
sector. From these, the corresponding baryon properties are constructed. We
present results for the higher order moments of the spin-3/2 baryons, including
the electric quadrupole moment E2 and the magnetic octupole moment M3. The
world's first determination of a non-zero M3 form factor for the Delta baryon
is presented. With these results we provide a conclusive analysis which shows
that decuplet baryons are deformed. We compare the decuplet baryon results from
a similar lattice calculation of the octet baryons. We establish that the
environment sensitivity is far less pronounced in the case of the decuplet
baryons compared to that in the octet baryons. A surprising result is that the
charge radii of the decuplet baryons are generally smaller than that of the
octet baryons. The magnetic moment of the Delta^+ reveals a turn over in the
low quark mass region, making it smaller than the proton magnetic moment. These
results are consistent with the expectations of quenched chiral perturbation
theory. A similar turn over is also noticed in the magnetic moment of the
Sigma^*0, but not for Xi^* where only kaon loops can appear in quenched QCD.
The electric quadrupole moment of the Omega^- baryon is positive when the
negative charge factor is included, and is equal to 0.86 +- 0.12 x 10^-2 fm^2,
indicating an oblate shape.Comment: 30 pages, 32 figure
Quark propagator in a covariant gauge
Using mean--field improved gauge field configurations, we compare the results
obtained for the quark propagator from Wilson fermions and Overlap fermions on
a \3 lattice at a spacing of fm.Comment: 5 pages, 8 figures, talk given by F.D.R. Bonnet at LHP 2001 workshop,
Cairns, Australi
Accessing High Momentum States In Lattice QCD
Two measures are defined to evaluate the coupling strength of smeared
interpolating operators to hadronic states at a variety of momenta. Of
particular interest is the extent to which strong overlap can be obtained with
individual high-momentum states. This is vital to exploring hadronic structure
at high momentum transfers on the lattice and addressing interesting phenomena
observed experimentally. We consider a novel idea of altering the shape of the
smeared operator to match the Lorentz contraction of the probability
distribution of the high-momentum state, and show a reduction in the relative
error of the two-point function by employing this technique. Our most important
finding is that the overlap of the states becomes very sharp in the smearing
parameters at high momenta and fine tuning is required to ensure strong overlap
with these states.Comment: 10 page
Light-Quark FLIC Fermion Simulations of the Exotic Meson
We investigate the mass of the exotic meson, created with hybrid
interpolating fields. Access to light quark masses approaching 25 MeV is
facilitated by the use of the Fat-Link Irrelevant Clover (FLIC) fermion action,
and large () lattices. Our results indicate that the
exotic exhibits significant curvature close to the chiral limit, and yield a
mass in agreement with the candidate and exclusive of
the .Comment: 6 pages, 1 table, 2 figures, talk given at Lattice '05. Removed
unccessary figure
Scaling of FLIC Fermions
Hadron masses are calculated in quenched lattice QCD on a variety of lattices
in order to probe the scaling behavior of the Fat-Link Irrelevant Clover (FLIC)
fermion action, a fat-link clover fermion action in which the purely irrelevant
operators of the fermion action are constructed using APE-smeared links. The
scaling analysis indicates FLIC fermions provide a new form of nonperturbative
O(a) improvement where near-continuum results are obtained at finite lattice
spacing.Comment: 4 pages, 1 figure, 2 tables. Figure updated and references added.
Accepted for publication in Phys. Rev.
Precision Electromagnetic Structure of Octet Baryons in the Chiral Regime
The electromagnetic properties of the baryon octet are calculated in quenched
QCD on a 20^3 x 40 lattice with a lattice spacing of 0.128 fm using the
fat-link irrelevant clover (FLIC) fermion action. FLIC fermions enable
simulations to be performed efficiently at quark masses as low as 300 MeV. By
combining FLIC fermions with an improved-conserved vector current, we ensure
that discretisation errors occur only at O(a^2) while maintaining current
conservation. Magnetic moments and electric and magnetic radii are extracted
from the electric and magnetic form factors for each individual quark sector.
From these, the corresponding baryon properties are constructed. Our results
are compared extensively with the predictions of quenched chiral perturbation
theory. We detect substantial curvature and environment sensitivity of the
quark contributions to electric charge radii and magnetic moments in the low
quark mass region. Furthermore, our quenched QCD simulation results are in
accord with the leading non-analytic behaviour of quenched chiral perturbation
theory, suggesting that the sum of higher-order terms makes only a small
contribution to chiral curvature.Comment: 29 pages, 33 figures, 20 table
Some continuum physics results from the lattice V-A correlator
We present preliminary results on extractions of the chiral LECs L_10 and
C_87 and constraints on the excited pseudoscalar state pi(1300) and pi(1800)
decay constants obtained from an analysis of lattice data for the flavor ud
light quark V-A correlator. A comparison of the results for the correlator to
the corresponding mildly-model-dependent continuum results (based primarily on
experimental hadronic tau decay data) is also givenComment: 7 pages, 3 figures. Prepared for the Proceedings of the 30th
International Symposium on Lattice Field Theory, Cairns, Australia, June
24-29, 2012; expanded version of Reference 1
New results from the lattice on the theoretical inputs to the hadronic tau determination of V_us
Recent sum rule determinations of |V_us|, employing flavor-breaking
combinations of hadronic tau decay data, are significantly lower than either
expectations based on 3-family unitarity or determinations from K_ell3 and
Gamma[K_mu2]/Gamma[pi_mu2]. We use lattice data to investigate the
accuracy/reliability of the OPE representation of the flavor-breaking
correlator combination entering the tau decay analyses. The behavior of an
alternate correlator combination, constructed to reduce problems associated
with the slow convergence of the D = 2 OPE series, and entering an alternate
sum rule requiring both electroproduction cross-section and hadronic tau decay
data, is also investigated. Preliminary updates of both analyses, with the
lessons learned from the lattice data in mind, are also presented.Comment: 8 pages, 5 figures. Prepared for the proceedings of the 12th
International Workshop on Tau Lepton Physics, Sep. 17-21, 2012, Nagoya, Japan
and the 10th International Conference on Confinement and the Hadron Spectrum,
Oct. 6-13, 2012, Garching/Munich, German
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