58 research outputs found
Chiral loop corrections to weak decays of B mesons to positive and negative parity charmed mesons
We determine chiral loop corrections to the B meson decay amplitudes to
positive and negative parity charmed mesons within a framework which combines
heavy quark and chiral symmetries. Then we investigate the impact of the
lowest-lying positive parity heavy mesons on the determination of the
Isgur-Wise functions. The corrections due to these states are competitive with
the contributions arising from K and eta meson loops. Since lattice studies
rely on the chiral behavior of the amplitudes we discuss the chiral limit of
our results. We find that the determination of the slope at zero recoil of the
Isgur-Wise function xi for the B transition to negative parity charm mesons is
moderately affected by the inclusion of new states, while the slope of
tau_{1/2} is affected significantly more.Comment: 10 pages, 4 figure
The Ademollo-Gatto theorem for lattice semileptonic decays
We present the results of the calculation of the Kl3 semileptonic form factor
at zero momentum transfer, f(0), obtained at one-loop in partially quenched
Chiral Perturbation Theory (with either Nf=2, or Nf=3, and with generic valence
and sea quark masses). We show that for Nf=2, when the masses of the valence
and sea light quarks are equal, the correction is of the order (MK^2-Mpi^2)^3.
The formulae presented here can be useful for the mass extrapolation of the
results obtained in lattice simulations to the physical point.Comment: 7 page
Continuum Determination of Light Quark Masses from Quenched Lattice QCD
We compute the strange and the average up/down quark masses in the quenched
approximation of lattice QCD, by using the O(a)-improved Wilson action and
operators and by implementing the non-perturbative renormalization. Our
computation is performed at four values of the lattice spacing, from which we
could extrapolate to the continuum limit. Our final result for the strange
quark mass (in the MSbar scheme) is ms(2 GeV) = (106 +/- 2 +/- 8) MeV. For the
average up/down quark mass we have ml(2 GeV) = (4.4 +/- 0.1 +/- 0.4) MeV. The
ratio ms/ml = (24.3 +/- 0.2 +/- 0.6).Comment: 14 pages, 3 PostScript figure
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
Constraints on R-parity violating supersymmetry from neutral meson mixing
Upper bounds at the weak scale are put on all
type products of R-parity violating supersymmetry that may affect K-Kbar and
B-Bbar mixing. We constrain all possible products, including some not
considered before, using next-to-leading order QCD corrections to the mixing
amplitudes. Constraints are obtained for both real and imaginary parts of the
couplings. We also discuss briefly some correlated decay channels which should
be investigated in future experiments.Comment: 13 pages, 2 figures, uses revtex. Constraints updated, and new
constraints adde
Remarks on the hadronic matrix elements relevant to the SUSY K-Kbar mixing amplitude
We compute the 1-loop chiral corrections to the bag parameters which are
needed for the discussion of the SUSY K-Kbar mixing problem in both finite and
infinite volume. We then show how the bag parameters can be combined among
themselves and with some auxiliary quantities and thus sensibly reduce the
systematic errors due to chiral extrapolations as well as those due to finite
volume artefacts present in the results obtained from lattice QCD. We also show
that in some cases these advantages remain as such even after including the
2-loop chiral corrections. Similar discussion is also made for the K --> pi
electro-weak penguin operators.Comment: 13 pages, 3 figures [added 1 reference and a discussion about the
impact of the NNLO chiral corrections to the "golden ratios" (c.f. Sec.6)
Semileptonic Hyperon Decays on the Lattice: an Exploratory Study
We present preliminary results of an exploratory lattice study of the vector
form factor relevant for the semileptonic hyperon decay
. This study is based on the same method used for the
extraction of for the decay . The main purpose
of this study is to test the method for hyperon form factors in order to
estimate the precision that can be reached and the importance of SU(3)-breaking
effects.Comment: 3 pages, 5 figures, talk presented at Lattice2004(weak), Fermilab,
Batavia, Illinois, 21-26 June 200
B Physics on the Lattice: Present and Future
Recent experimental measurements and lattice QCD calculations are now
reaching the precision (and accuracy) needed to over-constrain the CKM
parameters and . In this brief review, I discuss the
current status of lattice QCD calculations needed to connect the experimental
measurements of meson properties to quark flavor-changing parameters.
Special attention is given to , which is becoming a competitive
way to determine , and to mixings, which now include
reliable extrapolation to the physical light quark mass. The combination of the
recent measurement of the mass difference and current lattice
calculations dramatically reduces the uncertainty in . I present an
outlook for reducing dominant lattice QCD uncertainties entering CKM fits, and
I remark on lattice calculations for other decay channels.Comment: Invited brief review for Mod. Phys. Lett. A. 15 pages. v2: typos
corrected, references adde
A strategy for implementing non-perturbative renormalisation of heavy-light four-quark operators in the static approximation
We discuss the renormalisation properties of the complete set of four-quark operators with the heavy quark treated in the static
approximation. We elucidate the role of heavy quark symmetry and other symmetry
transformations in constraining their mixing under renormalisation. By
employing the Schroedinger functional, a set of non-perturbative
renormalisation conditions can be defined in terms of suitable correlation
functions. As a first step in a fully non-perturbative determination of the
scale-dependent renormalisation factors, we evaluate these conditions in
lattice perturbation theory at one loop. Thereby we verify the expected mixing
patterns and determine the anomalous dimensions of the operators at NLO in the
Schroedinger functional scheme. Finally, by employing twisted-mass QCD it is
shown how finite subtractions arising from explicit chiral symmetry breaking
can be avoided completely.Comment: 41 pages, 6 figure
B-parameters of the complete set of matrix elements of (Delta B = 2) operators from the lattice
We compute on the lattice the ``bag'' parameters of the five (Delta B = 2)
operators of the supersymmetric basis, by combining their values determined in
full QCD and in the static limit of HQET. The extrapolation of the QCD results
from the accessible heavy-light meson masses to the B-meson mass is constrained
by the static result. The matching of the corresponding results in HQET and in
QCD is for the first time made at NLO accuracy in the MSbar(NDR)
renormalization scheme. All results are obtained in the quenched approximation.Comment: 27 pages (5 figures
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