2,428 research outputs found
Renormalization constants of local operators within the Schr\"odinger functional scheme
We define, within the Schr\"odinger functional (SF) scheme, the matrix
elements of the twist-2 operators corresponding to the first two moments of
non-singlet parton density, and the first moment of singlet parton densities.
We perform a lattice one-loop calculation that fixes the relation between the
SF scheme and other common schemes and shows the main source of lattice
artefacts. Few remarks on the improvement case are added.Comment: Presented at LATTICE99, 3 page
Moments of parton evolution probabilities on the lattice within the Schroedinger functional scheme
We define, within the Schroedinger functional scheme (SF), the matrix
elements of the twist-2 operators corresponding to the first two moments of
non-singlet parton densities. We perform a lattice one-loop calculation that
fixes the relation between the SF scheme and other common schemes and shows the
main source of lattice artefacts. This calculation sets the basis for a
numerical evaluation of the non-perturbative running of parton densities.Comment: Latex file, 4 figures, 15 page
Unstable particles in finite volume: The broken phase of the -d non-linear -model
According to a proposal of L\"uscher it is possible to determine elastic
scattering phases in infinite volume from the energy spectrum of two-particle
states in a periodic box.
We demonstrate the applicability of this method in the broken phase of the
4-dimensional non-linear -model in a Monte-Carlo study on finite
lattices.
This non-perturbative approach also permits the study of unstable particles,
the \sg-particle in our case. We observe the \sg-resonance and extract its
mass and its width.Comment: 4 pages LaTeX, 4 PS figures, LATTICE'92 contributio
Matching the High Momentum Modes in a Truncated Determinant Algorithm
Within a truncated determinant algorithm, two alternatives are discussed for
including systematically the remaining ultraviolet modes. Evidence is presented
that these modes are accurately described by an effective action involving only
small Wilson loops.Comment: LATTICE98(algorithms) ; typos correcte
A perturbative determination of O(a) boundary improvement coefficients for the Schr\"odinger Functional coupling at 1-loop with improved gauge actions
We determine O() boundary improvement coefficients up to 1-loop level for
the Schr\"odinger Functional coupling with improved gauge actions including
plaquette and rectangle loops. These coefficients are required to implement
1-loop O() improvement in full QCD simulations for the coupling with the
improved gauge actions. To this order, lattice artifacts of step scaling
function for each improved gauge action are also investigated. In addition,
passing through the SF scheme, we estimate the ratio of -parameters
between the improved gauge actions and the plaquette action more accurately.Comment: 17 pages, 2 figures, 6 table
Two loop expansion of the Schroedinger functional coupling alpha_SF in SU(3) lattice gauge theory
The two loop coefficient of the expansion of the Schroedinger functional
coupling in terms of the lattice coupling is calculated for the SU(3)
Yang-Mills theory. This coefficient is required to relate lattice data to the
MS-bar-coupling. As a byproduct of the calculation, the Schroedinger functional
is improved to two loop order and the three loop coefficient of the beta
function in the SF-scheme is derived.Comment: 3 pages, 1 figures (postscript), uses epsf.sty, Contribution to
Lattice 97, email [email protected]
Lattice QCD without topology barriers
As the continuum limit is approached, lattice QCD simulations tend to get
trapped in the topological charge sectors of field space and may consequently
give biased results in practice. We propose to bypass this problem by imposing
open (Neumann) boundary conditions on the gauge field in the time direction.
The topological charge can then flow in and out of the lattice, while many
properties of the theory (the hadron spectrum, for example) are not affected.
Extensive simulations of the SU(3) gauge theory, using the HMC and the closely
related SMD algorithm, confirm the absence of topology barriers if these
boundary conditions are chosen. Moreover, the calculated autocorrelation times
are found to scale approximately like the square of the inverse lattice
spacing, thus supporting the conjecture that the HMC algorithm is in the
universality class of the Langevin equation.Comment: Plain TeX source, 26 pages, 4 figures include
The Sub-leading Magnetic Deformation of the Tricritical Ising Model in 2D as RSOS Restriction of the Izergin-Korepin Model
We compute the -matrix of the Tricritical Ising Model perturbed by the
subleading magnetic operator using Smirnov's RSOS reduction of the
Izergin-Korepin model. We discuss some features of the scattering theory we
obtain, in particular a non trivial implementation of crossing-symmetry,
interesting connections between the asymptotic behaviour of the amplitudes, the
possibility of introducing generalized statistics, and the monodromy properties
of the OPE of the unperturbed Conformal Field Theory.Comment: (13 pages
The three-loop beta-fuction of QCD with the clover action
We calculate, to 3 loops in perturbation theory, the bare -function of
QCD, formulated on the lattice with the clover fermionic action. The dependence
of our result on the number of colors , the number of fermionic flavors
, as well as the clover parameter , is shown explicitly.
A direct outcome of our calculation is the two-loop relation between the bare
coupling constant and the one renormalized in the MS-bar scheme.
Further, we can immediately derive the three-loop correction to the relation
between the lattice -parameter and , which is important in checks
of asymptotic scaling. For typical values of , this correction is found
to be very pronounced.Comment: 14 pages, 2 eps figure
The gradient flow running coupling with twisted boundary conditions
We study the gradient flow for Yang-Mills theories with twisted boundary
conditions. The perturbative behavior of the energy density is used to define a running coupling at a scale given by the
linear size of the finite volume box. We compute the non-perturbative running
of the pure gauge coupling constant and conclude that the technique is
well suited for further applications due to the relatively mild cutoff effects
of the step scaling function and the high numerical precision that can be
achieved in lattice simulations. We also comment on the inclusion of matter
fields.Comment: 27 pages. LaTe
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