Searcharxiv⌕ Search

arXiv subjects

SESAM-Collaboration

Publications and source records attributed to SESAM-Collaboration.

5 recordsLinked to original sources
arXiv1998

The Pion-Nucleon sigma-Term with Dynamical Wilson Fermions

We calculate connected and disconnected contributions to the flavour singlet scalar density amplitude of the nucleon in a full QCD lattice simulation with $n_f=2$ dynamical Wilson fermions at $β=5.6$ on a $16^3 \times 32$ lattice. We find that both contributions are of similar size at the light quark mass. We arrive at the estimate $σ_{πN} = 18(5)$MeV. Its smallness is directly related to the apparent decrease of $u$, $d$ quark masses when unquenching QCD lattice simulations. The $y$ parameter can be estimated from a semi-quenched analysis, in which there are no strange quarks in the sea, the result being $y=0.59(13)$.}

hep-lat↗
arXiv1996

Evaluating Sea Quark Contributions to Flavour-Singlet Operators in Lattice QCD

In a full QCD lattice study with $N_f = 2$ Wilson fermions, we seek to optimize the signals for the disconnected contributions to the matrix element of flavour-singlet operators between nucleon states, which are indicative for sea quark effects. We demonstrate, in form of a fluctuation analysis to the noisy estimator technique, that -- in order to achieve a tolerable signal to noise-ratio in full QCD -- it is advantageous to work with a $Z_2$-noise source rather than to rely only on gauge invariance to cancel non-gauge-invariant background. In the case of the $π$N $σ$-term, we find that 10 $Z_2$-noise sources suffice on our sample ( about 150 independent QCD configurations at $β= 5.6$ on $16^3\times32$ with $κ_{sea} = 0.157$, equivalent to $M_π/M_ρ = 0.76(1)$), to achieve decent signals and adequate fluctuations, rather than 300 such sources as recently used in quenched simulations.

hep-lat↗
arXiv1995

QCD with dynamical Wilson fermions - first results from SESAM

First results of a recently started simulation of full QCD with two flavours of sea-quarks at a coupling of $β= 5.6$ on a $16^3 \times 32$ lattice are presented. Emphasis is laid on the statistical significance that can be achieved by an ``integrated luminosity'' of 140 TFlop$\times$hrs, for Hybrid Monte Carlo simulations at four intermediate values of $\frac{m_π}{m_ρ}$. The simulation takes place on the Quadrics QH2 at DESY/Zeuthen and DFG/Bielefeld. The performance is optimized by means of BiCGStab and the chronological inversion method of Brower et al. We discuss the systematic errors arising from lack of the molecular dynamic's reversibility on the 32-bit QH2. For plaquette and meson correlators we find integrated autocorrelation times of $< 20$ units of molecular dynamics time and exponential autocorrelation times of about $50$ units. Using these results we perform preliminary measurements of the central potential and $π$ and $ρ$ correlators on independent configurations and obtain first estimates of the lattice spacings at three values of the dynamical hopping parameter.

hep-lat↗