1,127 research outputs found
Momentum-dependence of charmonium spectral functions from lattice QCD
We compute correlators and spectral functions for J/psi and eta_c mesons at
nonzero momentum on anisotropic lattices with Nf=2. We find no evidence of
significant momentum dependence at the current level of precision. In the
pseudoscalar channel, the ground state appears to survive up to T~450MeV or
2.1T_c. In the vector channel, medium modifications may occur at lower
temperatures.Comment: 5 pages, 12 figure
An Improved Action for Heavy Quarks
We extend the Fermilab method for heavy quarks to include all interactions of
dimension six in the action. We discuss a subtlety in the power counting, which
implies that, for heavy quarks, certain interactions of dimension seven are
commensurate with some of those of dimension six. We then present tree-level
matching conditions obtained from calculating the Compton scattering amplitude
for (lattice) QCD. When the matching conditions have been applied, the improved
action removes (tree-level) discretization errors of order
and .Comment: 1+5 pp., contribution to Lattice 2006(Quark Masses, Gauge Couplings,
and Renormalization
Accurate Checks of Universality for Dyson's Hierarchical Model
Using recently developed methods, we perform high-accuracy calculations of
the susceptibility near beta_c for the D=3 version of Dyson's hierarchical
model. Using linear fits, we estimate the leading gamma and subleading Delta
exponents. Independent estimates are obtained by calculating the first two
eigenvalues of the linearized renormalization group transformation. We found
gamma = 1.29914073 (with an estimated error of 10^{-8}) and, Delta=0.4259469
(with an estimated error of 10^{-7}) independently of the choice of local
integration measure (Ising or Landau-Ginzburg). After a suitable rescaling, the
approximate fixed points for a large class of local measure coincide accurately
with a fixed point constructed by Koch and Wittwer.Comment: 9 pages, Revtex, 1 figur
Numerical Tests of the Improved Fermilab Action
Recently, the Fermilab heavy-quark action was extended to include
dimension-six and -seven operators in order to reduce the discretization
errors. In this talk, we present results of the first numerical simulations
with this action (the OK action), where we study the masses of the quarkonium
and heavy-light systems. We calculate combinations of masses designed to test
improvement and compare results obtained with the OK action to their
counterparts obtained with the clover action. Our preliminary results show a
clear improvement.Comment: 7 pages, 3 figures, Talk presented at 28th International Symposium On
Lattice Field Theory (Lattice 2010) 13-19 Jun 2010, Villasimius, Sardinia,
Ital
The spectrum of radial, orbital and gluonic excitations of charmonium
We present results for the charmonium spectrum from dynamical QCD
simulations on anisotropic lattices. Using all-to-all
propagators we determine the ground and excited states of S, P and D waves and
hybrids. We also evaluate the disconnected (OZI suppressed) contribution to the
and Comment: 6 pages, 3 figures, Presented at 24th International Symposium on
Lattice Field Theory (Lattice 2006), Tucson, Arizona, 23-28 Jul 200
High-accuracy critical exponents of O(N) hierarchical sigma models
We perform high-accuracy calculations of the critical exponent gamma and its
subleading exponent for the 3D O(N) Dyson's hierarchical model, for N up to 20.
We calculate the critical temperatures for the nonlinear sigma model measure.
We discuss the possibility of extracting the first coefficients of the 1/N
expansion from our numerical data. We show that the leading and subleading
exponents agreewith Polchinski equation and the equivalent Litim equation, in
the local potential approximation, with at least 4 significant digits.Comment: 4 pages, 2 Figs., uses revte
Palynological analysis of Upper Ordovician to Lower Silurian sediments from the Diyarbakir Basin, southeastern Turkey
This paper reports on a palynological analysis of 41 core and 21 cutting samples from a well drilled through an Upper Ordovician–Lower Silurian sequence, belonging to the Bedinan and Dadas formations, of the Diyarbakır Basin of southeastern Turkey. The samples yield abundant and well-preserved marine palynomorphs (acritarchs, chitinozoans and scolecodonts) although non-marine palynomorphs (spores/cryptospores) are extremely rare or absent. The Upper Ordovician sediments of the Bedinan Formation have low organic content but contain abundant palynomorphs whereas the Lower Silurian sediments of the Dadas Formation have high organic content, dominated by amorphous organic matter, with relatively rare palynomorphs. Three chitinozoan assemblages are identified and attributed a late Katian (merga Biozone), Hirnantian (moussegoudaensis Biozone) and Llandovery (?alargada Biozone) age. Two acritarch assemblages are identified and attributed a Katian–Hirnantian and Llandovery (Aeronian–Telychian) age. The chitinozoan and acritarch age determinations are compatible and suggest that the Bedinan Formation is of Katian–Hirnantian age and is separated by an unconformity from the Dadas Formation that is of Llandovery (Aeronian–Telychian) age. These findings confirm the presence of an unconformity at the Ordovician–Silurian transition in the southeastern Turkey. Palynofacies analysis suggests that the Bedinan Formation accumulated on an offshore shelf that was initially well oxygenated but became increasingly anoxic, whereas the Dadas Formation accumulated in an offshore basin that was anoxic. Palynomorph assemblages recorded in the Bedinan and Dadas formations indicate northern Gondwana affinity
Spectral functions of charmonium from 2 flavour anisotropic lattice data
The spectral functions of QCD can give us insight into properties of hadrons,
and they are useful in probing the QCD vacuum. I will discuss the correlators
and spectral functions of charmonium in high temperature two flavour QCD. The
spectral functions have been obtained using the Maximum Entropy Method from
anisotropic lattice data using the conserved vector current. This work has been
done as part of the FASTSUM collaboration. We find that the spectral functions
for zero momentum are stable. At non-zero momentum the spectral functions are
less stable but still produce resonance and transport peaks. This work is part
of our programme to calculate the heavy quark diffusion constant.Comment: 7 pages, 5 figures, 31st International Symposium on Lattice Field
Theory LATTICE 201
- …