200 research outputs found
Non-Perturbative Renormalisation of the Lattice Four-Fermion Operator
We compute the renormalised four-fermion operator using a
non-perturbative method recently introduced for determining the renormalisation
constants of generic lattice composite operators. Because of the presence of
the Wilson term, mixes with operators of different
chiralities. A projection method to determine the mixing coefficients is
implemented. The numerical results for the renormalisation constants have been
obtained from a simulation performed using the SW-Clover quark action, on a
lattice, at . We show that the use of the constants
determined non-perturbatively improves the chiral behaviour of the lattice kaon
matrix element \_{\latt}.Comment: LaTeX, 16 pages, 2 postscript figure
Quark masses and the chiral condensate with a non-perturbative renormalization procedure
We determine the quark masses and the chiral condensate in the MSbar scheme
at NNLO from Lattice QCD in the quenched approximation at beta=6.0, beta=6.2
and beta=6.4 using both the Wilson and the tree-level improved SW-Clover
fermion action. We extract these quantities using the Vector and the Axial Ward
Identities and non-perturbative values of the renormalization constants. We
compare the results obtained with the two methods and we study the O(a)
dependence of the quark masses for both actions.Comment: LATTICE98(spectrum), 3 pages, 1 figure, Edinburgh 98/1
Non-perturbative Renormalization of the Complete Basis of Four-fermion Operators and B-parameters
We present results on the B-parameters , and , at
, with the tree-level Clover action. The renormalization of the
complete basis of dimension-six four-fermion operators has been performed
non-perturbatively. Our results for and are in reasonable
agreement with those obtained with the (unimproved) Wilson action. This is not
the case for . We also discuss some subtleties arising from a
recently proposed modified definition of the B-parameters.Comment: Talk presented at Lattice '97, Edinburgh (UK), July 1997. LaTeX 3
pages, uses espcrc
Non-perturbative renormalization in kaon decays
We discuss the application of the MPSTV non-perturbative method \cite{NPM} to
the operators relevant to kaon decays. This enables us to reappraise the
long-standing question of the rule, which involves
power-divergent subtractions that cannot be evaluated in perturbation theory.
We also study the mixing with dimension-six operators and discuss its
implications to the chiral behaviour of the parameter.Comment: Talk presented at LATTICE96(improvement), LaTeX 3 pages, uses
espcrc2, 2 postscript figure
Delta M_K and epsilon_K in SUSY at the Next-to-Leading order
We perform a Next-to-Leading order analysis of Delta S=2 processes beyond the
Standard Model. Combining the recently computed NLO anomalous dimensions and
the B parameters of the most general Delta S=2 effective Hamiltonian, we give
an analytic formula for Delta M_K and epsilon_K in terms of the Wilson
coefficients at the high energy scale. This expression can be used for any
extension of the Standard Model with new heavy particles. Using this result, we
consider gluino-mediated contributions to Delta S=2 transitions in general SUSY
models and provide an improved analysis of the constraints on off-diagonal mass
terms between the first two generations of down-type squarks. Finally, we
improve the constraints on R-violating couplings from Delta M_K and epsilon_K.Comment: 20 pages, 1 figure, uses JHEP.cls; the magic numbers in eq. (2.7),
previously given in the basis (13) of hep-ph/9711402, are now given in the
basis (2.3) of this work. All numerical results are unchange
Non-perturbative renormalization of lattice four-fermion operators without power subtractions
A general nonperturbative analysis of the renormalization properties of Delta I = 3/2 four-fermion operators in the framework of lattice regularization with Wilson fermions is presented. We discuss the nonperturbative determination of the operator renormalization constants in the lattice regularization independent (RI or MOM) scheme. We also discuss the determination of the finite lattice subtraction coefficients from Ward identities. We prove that, at large external virtualities, the determination of the lattice mixing coefficients, obtained using the RI renormalization scheme, is equivalent to that based on Ward identities, in the continuum and chiral limits. As a feasibility study of our method, we compute the mixing matrix at several renormalization scales, for three Values of the lattice coupling beta, using the Wilson and tree-level improved SW-Clover actions
String Breaking in Quenched QCD
We present preliminary quenched results on a new operator for the
investigation of string-breaking within SU(2)-colour QCD. The ground-state of a
spatially-separated static-light meson-antimeson pair is a combination of a
state with two distinct mesons, expected to dominate for large separations, and
a state where the light-quarks have annihilated, which contributes for short
distances. The crossover between these two regimes provides a measure of the
string-breaking scale length.Comment: LATTICE98(confine), 3 pages, 4 figure
Lattice B-parameters for and Operators
We compute several matrix elements of dimension-six four-fermion operators
and extract their B-parameters. The calculations have been performed with the
tree-level Clover action at . The renormalization constants and
mixing coefficients of the lattice operators have been obtained
non-perturbatively. In the \MSbar renormalization scheme, at a
renormalization scale GeV, we find and . The result for has
important implications for the calculation of .Comment: LaTeX, 14 pages, revised version (sign misprint in eq. (21)
corrected
On the Thermodynamic Limit in Random Resistors Networks
We study a random resistors network model on a euclidean geometry \bt{Z}^d.
We formulate the model in terms of a variational principle and show that, under
appropriate boundary conditions, the thermodynamic limit of the dissipation per
unit volume is finite almost surely and in the mean. Moreover, we show that for
a particular thermodynamic limit the result is also independent of the boundary
conditions.Comment: 14 pages, LaTeX IOP journal preprint style file `ioplppt.sty',
revised version to appear in Journal of Physics
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