240 research outputs found
The Nambu-Jona-Lasinio model with staggered fermions
We investigate the neighbourhood of the chiral phase transition in a lattice
Nambu--Jona-Lasinio model, using both Monte Carlo methods and lattice
Schwinger-Dyson equations.Comment: Talks at LAT93, Dallas, U.S.A. Postscript file, 6 pages, figures
include
Resolution of the Landau pole problem in QED
We present new numerical results for the renormalized mass and coupling in
non-compact lattice QED with staggered fermions. Implications for the continuum
limit and the role of the Landau pole are discussed.Comment: 3 pages, talk presented by H. St\"uben at Lattice '97, Edinburg
Baryonic Flux in Quenched and Two-Flavor Dynamical QCD after Abelian projection
We study the distribution of color electric flux of the three-quark system in
quenched and full QCD (with N_f = 2 flavors of dynamical quarks) at zero and
finite temperature. To reduce ultra-violet fluctuations, the calculations are
done in the abelian projected theory fixed to the maximally abelian gauge. In
the confined phase we find clear evidence for a Y--shape flux tube surrounded
and formed by the solenoidal monopole current, in accordance with the dual
superconductor picture of confinement. In the deconfined, high temperature
phase monopoles cease to condense, and the distribution of the color electric
field becomes Coulomb--like.Comment: 21 pages, 15 figures, Latex, published version (4 figures added
The present status of non-compact lattice QED
We give a 1993 update of non-compact lattice QED, in particular the chiral
condensate, finite size effects and meson mass ratios.
We compare descriptions of the phase transition. Our previous conclusions
remain valid.Comment: Poster presentation at LAT93, Dallas, U.S.A. Postscript file, 4
pages, figures included. Preprint numbers DESY-93-178, FUB-HEP/93-20 and HLRZ
93-7
Progress towards a lattice determination of (moments of) nucleon structure functions
Using unimproved and non-perturbatively O(a) improved Wilson fermions,
results are given for the three lowest moments of unpolarised nucleon structure
functions. Renormalisation, chiral extrapolation and the continuum limit of the
matrix elements are briefly discussed. The simulations are performed for both
quenched and two flavours of unquenched fermions. No obvious sign of deviation
from linearity in the chiral extrapolations are found. (This is most clearly
seen in our quenched unimproved data, which extends to lighter quark mass.)
Possible quenching effects also seem to be small. The lowest moment thus
remains too large, so it seems to be necessary to reach smaller quark masses in
numerical simulations.Comment: 3 pages, Latex, 4 figures, Talk presented at
Lattice2001(matrixelement
Accelerating Hasenbusch's acceleration of Hybrid Monte Carlo
Hasenbusch has proposed splitting the pseudo-fermionic action into two parts,
in order to speed-up Hybrid Monte Carlo simulations of QCD. We have tested a
different splitting, also using clover-improved Wilson fermions. An additional
speed-up between 5 and 20% over the original proposal was achieved in
production runs.Comment: Poster presented by H. Stueben at Lattice2003, meta-data correcte
A Determination of the Lambda Parameter from Full Lattice QCD
We present a determination of the QCD parameter Lambda in the quenched
approximation (n_f=0) and for two flavours (n_f=2) of light dynamical quarks.
The calculations are performed on the lattice using O(a) improved Wilson
fermions and include taking the continuum limit. We find Lambda_{n_f=0} =
259(1)(20) MeV and Lambda_{n_f=2} = 261(17)(26) MeV}, using r_0 = 0.467 fm to
set the scale. Extrapolating our results to five flavours, we obtain for the
running coupling constant at the mass of the Z boson alpha_s(m_Z) =
0.112(1)(2). All numbers refer to the MSbar scheme.Comment: 25 pages, 9 figure
Determining the scale in Lattice QCD
We discuss scale setting in the context of 2+1 dynamical fermion simulations
where we approach the physical point in the quark mass plane keeping the
average quark mass constant. We have simulations at four beta values, and after
determining the paths and lattice spacings, we give an estimation of the
phenomenological values of various Wilson flow scales.Comment: 7 pages; talk presented at Lattice 2015, the 33rd International
Symposium on Lattice Field Theory 4 -18 July 2015 at Kobe International
Conference Center, Kobe, Japan; PoS(LATTICE2015)26
Probing the Continuum Limit in Non-Compact QED: New Results on Large Lattices
We present new Monte Carlo results in non-compact lattice QED with staggered
fermions down to m_0 = 0.005. This extends our previous investigations on the
nature of the continuum limit of QED.Comment: 7 pages, uuencoded compressed PostScript, also available at
ftp://ftp.zib-berlin.de/pub/zib-publications/Reports/SC-94-31.ps.
Investigation of the Second Moment of the Nucleon's g1 and g2 Structure Functions in Two-Flavor Lattice QCD
The reduced matrix elements a_2 and d_2 are computed in lattice QCD with
N_f=2 flavors of light dynamical (sea) quarks. For proton and neutron targets
we obtain as our best estimates d_2^(p)=0.004(5) and d_2^(n)=-0.001(3),
respectively, in the MSbar scheme at Q^2=5 GeV^2, while for a_2 we find
a_2^(p)=0.077(12) and a_2^(n)=-0.005(5), where the errors are purely
statistical.Comment: 9 pages, 9 figures, 5 tables, revised version: estimate of systematic
uncertainty in chiral extrapolation, 2 references added, version to appear in
Phys.Rev.
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