4,712 research outputs found

### Positivity and topology in lattice gauge theory

The admissibility condition usually used to define the topological charge in
lattice gauge theory is incompatible with a positive transfer matrix.Comment: 6 pages, revtex; revision has some clarifications and additional
references, representing the final version to appear in Physical Revie

### The three-loop beta function of SU(N) lattice gauge theories with Wilson fermions

We calculate the third coefficient of the lattice beta function associated
with the Wilson formulation for both gauge fields and fermions. This allows us
to evaluate the three-loop correction (linear in $g_0^2$) to the relation
between the lattice Lambda-parameter and the bare coupling $g_0$, which is
important in order to verify asymptotic scaling predictions. Our calculation
also leads to the two-loop relation between the coupling renormalized in the
MSbar scheme and $g_0$.
The original version of this paper contained a numerical error in one of the
diagrams, which has now been corrected. The calculations, as well as the layout
of the paper have remained identical, but there are some important changes in
the numerical results.Comment: One 14-page LaTeX file, one PostScript file containing 2 figures.
Corrected a numerical error in one of the diagrams. The calculations, as well
as the layout of the paper have remained unaffected, but there are some
important changes in the numerical result

### Hadronic decay of a scalar B meson from the lattice

We explore the transitions B$(0^+)$ to B $\pi$ and B$_s(0^+)$ to B K from
lattice QCD with $N_f=2$ flavours of sea quark, using the static approximation
for the heavy quark. We evaluate the effective coupling constants, predicting a
B$(0^+)$ to B $\pi$ width of around 160 MeV. Our result for the coupling
strength adds to the evidence that the B$_s(0^+)$ meson is not predominantly a
molecular state (BK).Comment: 10 pages LATE

### Non perturbative determination of the running coupling constant in quenched SU(2)

Through a finite size renormalization group technique we calculate the
running coupling constant for quenched SU(2) with a few percent error over a
range of energy varying by a factor thirty. The definition is based on ratio of
correlations of Polyakov loops with twisted boundary conditions. The
extrapolation to the continuum limit is governed by corrections due to lattice
artifacts which are proportional to the square of the lattice spacing and
appears rather smooth.Comment: 18 pages of ps fil

### Finite temperature SU(2) gauge theory: critical coupling and universality class

We examine SU(2) gauge theory in 3+1 dimensions at finite temperature in the
vicinity of critical point. For various lattice sizes in time direction
($N_\tau=1,2,4,8$) we extract high precision values of the inverse critical
coupling and critical values of the 4-th order cumulant of Polyakov loops
(Binder cumulant). We check the universality class of the theory by comparing
the cumulant values to that of the 3D Ising model and find very good agreement.
The Polyakov loop correlators for the indicated lattices are also measured
and the string tension values extracted. The high precision values of critical
coupling and string tension allow us to study the scaling of dimensionless
$T_c/\sqrt{\sigma}$ ratio. The violation of scaling by <10% is observed as the
coupling is varied from weak to strong coupling regime.Comment: 17 pages, 9 figures, minor correction

### Hadronic decays from the lattice

I review the lattice QCD approach to determining hadronic decay transitions.
Examples considered include rho to pi pi; b_1 to pi omega; hybrid meson decays
and scalar meson decays. I discuss what lattices can provide to help understand
the composition of hadrons.Comment: 6 pages, presented at QNP06, June 200

### Leading Quenching Effects in the Proton Magnetic Moment

We present the first investigation of the extrapolation of quenched nucleon
magnetic moments in quenched chiral effective field theory. We utilize
established techniques in finite-range regularisation and compare with standard
dimensional regularisation methods. Finite-volume corrections to the relevant
loop integrals are also addressed. Finally, the contributions of dynamical sea
quarks to the proton moment are estimated using a recently discovered
phenomenological link between quenched and physical QCD.Comment: 9 pages, 11 figs; v2: revised finite volume discussio

### Light Quark Mass Reweighting

We present a systematic study of the effectiveness of light quark mass
reweighting. This method allows a single lattice QCD ensemble, generated with a
specific value of the dynamical light quark mass, to be used to determine
results for other, nearby light dynamical quark masses. We study two gauge
field ensembles generated with 2+1 flavors of dynamical domain wall fermions
with light quark masses m_l=0.02 (m_\pi=620 MeV) and m_l=0.01 (m_\pi=420 MeV).
We reweight each ensemble to determine results which could be computed directly
from the other and check the consistency of the reweighted results with the
direct results. The large difference between the 0.02 and 0.01 light quark
masses suggests that this is an aggressive application of reweighting as can be
seen from fluctuations in the magnitude of the reweighting factor by four
orders of magnitude. Never-the-less, a comparison of the reweighed topological
charge, average plaquette, residual mass, pion mass, pion decay constant, and
scalar correlator between these two ensembles shows agreement well described by
the statistical errors. The issues of the effective number of configurations
and finite sample size bias are discussed. An examination of the topological
charge distribution implies that it is more favorable to reweight from heavier
mass to lighter quark mass.Comment: 24 pages and 10 figure

### Comparing improved actions for SU(2)

In order to help the user in choosing the right action a performance
comparison is done for seven improved actions. Six of them are Symanzik
improved, one at tree-level and two at one-loop, all with or without tadpole
improvement. The seventh is an approximate fixed point action. Observables are
static on- and off-axis two-body potentials and four-body binding energies,
whose precision is compared when the same amount of computer time is used by
the programs.Comment: 3 pages, 3 colour eps figures. Presented at LATTICE9

### I=2 $\pi\pi$ scattering using G-parity boundary condition

To make the $\pi\pi$ state with non-zero relative momentum as the leading
exponential, we impose anti-periodic boundary condition on the pion, which is
implemented by imposing G-parity or H-parity on the quark fields at the
boundary. With this, we calculate the I=2 $\pi\pi$ phase shift from lattice
simulation by using L\"uscher's formula.Comment: Lattice 2003, 3 pages, 6 figure

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