715 research outputs found
Lattice renormalisation of O(a) improved heavy-light operators
The analytical expressions and the numerical values of the renormalisation
constants of improved static-light currents are given at one-loop
order of perturbation theory in the framework of Heavy Quark Effective Theory:
the static quark is described by the HYP action and the light quark is
described either with the Clover or the Neuberger action. These factors are
relevant to extract from a lattice computation the decay constants ,
and the set of bag parameters associated with
mixing phenomenology in the Standard Model and beyond.Comment: 16 pages, 2 figures, 4 tables; few comments and references added;
version to be published in Phys Rev
K-->pipi amplitudes from lattice QCD with a light charm quark
We compute the leading-order low-energy constants of the DeltaS=1 effective
weak Hamiltonian in the quenched approximation of QCD with up, down, strange,
and charm quarks degenerate and light. They are extracted by comparing the
predictions of finite volume chiral perturbation theory with lattice QCD
computations of suitable correlation functions carried out with quark masses
ranging from a few MeV up to half of the physical strange mass. We observe a
large DeltaI=1/2 enhancement in this corner of the parameter space of the
theory. Although matching with the experimental result is not observed for the
DeltaI=1/2 amplitude, our computation suggests large QCD contributions to the
physical DeltaI=1/2 rule in the GIM limit, and represents the first step to
quantify the role of the charm quark-mass in K-->pipi amplitudes.Comment: 4 pages, 1 figure. Minor modifications. Final version to appear on
PR
An innovative strategy for electrochemically-promoted addition reactions
A new strategy based on the catalytic release of the supporting electrolyte agent in the electrolysis medium proved to be effective for the direct electroactivation of suitable C–H acid-containing compounds vs. catalytic addition processes, under solvent-free conditions
Non-perturbative renormalization of moments of parton distribution functions
We compute non-perturbatively the evolution of the twist-2 operators
corresponding to the average momentum of non-singlet quark densities. The
calculation is based on a finite-size technique, using the Schr\"odinger
Functional, in quenched QCD. We find that a careful choice of the boundary
conditions, is essential, for such operators, to render possible the
computation. As a by-product we apply the non-perturbatively computed
renormalization constants to available data of bare matrix elements between
nucleon states.Comment: Lattice2003(Matrix); 3 pages, 3 figures. Talk by A.
Continuous external momenta in non-perturbative lattice simulations: a computation of renormalization factors
We discuss the usage of continuous external momenta for computing
renormalization factors as needed to renormalize operator matrix elements.
These kind of external momenta are encoded in special boundary conditions for
the fermion fields. The method allows to compute certain renormalization
factors on the lattice that would have been very difficult, if not impossible,
to compute with standard methods. As a result we give the renormalization group
invariant step scaling function for a twist-2 operator corresponding to the
average momentum of non-singlet quark densities.Comment: 28 pages, 10 figure
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