12,326 research outputs found
QCD Sum Rule Analysis of the Subleading Isgur-Wise Form Factor
We present a QCD sum rule calculation of the spin-symmetry violating
universal function , which appears at order in the
heavy quark expansion of meson form factors. This function vanishes in the
standard approximation, where radiative effects are neglected. For the first
time, the complete set of diagrams arising at order is evaluated. In
particular, we find at zero recoil, indicating
that corrections induced by the chromo-magnetic moment operator are
small.Comment: (10 pages, REVTEX, 2 figures not included) SLAC-PUB-5915,
WIS-92/70/Sep-P
Two-Loop Renormalization of Heavy--Light Currents at Order 1/m_Q in the Heavy-Quark Expansion
We present exact results, at next-to-leading order in renormalization-group
improved perturbation theory, for the Wilson coefficients appearing at order
1/m_Q in the heavy-quark expansion of heavy-light current operators. To this
end, we complete the calculation of the corresponding two-loop anomalous
dimension matrix. Our results are important for determinations of |V_{ub}|
using exclusive and inclusive semileptonic B decays. They are also relevant to
computations of the decay constant f_B based on a heavy-quark expansion.Comment: 16 pages, 2 figures; third author added and one reference updated,
results unchange
Impact of Four-Quark Shape Functions on Inclusive B Decay Spectra
It has recently been pointed out that a new class of subleading shape
functions involving B-meson matrix elements of non-local four-quark operators
contributes at order Lambda_{QCD}/m_b to B->X_u+l+nu decay distributions in the
endpoint region. The corresponding functions f_u(omega) and f_v(omega) are
estimated using the vacuum-insertion approximation. A numerical analysis of
various B->X_u+l+nu decay spectra suggests that these power corrections are
very small, below present theoretical uncertainties due to other subleading
shape-function contributions.Comment: 8 pages, 2 figures; minor revisions and figure added; version to
appear in Eur. Phys. J.
Form Factor Relations for Heavy-to-Light Transitions
Assuming simple properties of the spectator particle in weak decays the form
factors of hadronic current matrix elements are shown to be related to a single
universal function. The Isgur-Wise result for heavy-to-heavy transitions
follows as well as similar relations for heavy-to-light decay processes. The
approximation should hold for total energies of the final particle large
compared to the confinement scale. A comparison with experimentally determined
D-decay form factors and QCD sum rule results for B-decays is very encouraging.Comment: 12 pages, Latex; Relativistic covariant form, results unchanged,
references added, to be published in Physics Lett.
Effective Field Theory and Heavy Quark Physics
These notes are based on five lectures presented at the 2004 Theoretical
Advanced Study Institute (TASI) on ``Physics in D>=4''. After a brief
motivation of flavor physics, they provide a pedagogical introduction to
effective field theory, the effective weak Lagrangian, and the technology of
renormalization-group improved perturbation theory. These general methods are
then applied in the context of heavy-quarks physics, introducing the concepts
of heavy-quark and soft-collinear effective theory.Comment: Lectures presented at TASI 2004 (39 pages
Resummation of Renormalon Chains for Cross Sections and Inclusive Decay Rates
Recently, we have developed a formalism to evaluate QCD loop diagrams with a
single virtual gluon using a running coupling constant at the vertices. This
corresponds to an all-order resummation of certain terms (the so-called
renormalon chains) in a perturbative series and provides a generalization of
the scale-setting prescription of Brodsky, Lepage and Mackenzie. In its
original form, the method is applicable to Green functions without external
gluons and to euclidean correlation functions. Here we generalize the approach
to the case of cross sections and inclusive decay rates, which receive both
virtual and real gluon corrections. We encounter nonperturbative ambiguities in
the resummation of the perturbative series, which may hinder the construction
of the operator product expansion in the physical region. The origin of these
ambiguities and their relation to renormalon singularities in the Borel plane
is investigated by introducing an explicit infrared cutoff. The ratios and are discussed in detail.Comment: 37 pages LaTeX, uses epsf, 8 figures. Largely revised version with an
extended discussion and several new result
Theory of CP Violation in the B-Meson System
Recent developments in the theory of CP violation in the B-meson system are
reviewed, with focus on the determination of sin(2beta) from B-> J/psi K
decays, its implications for tests of the Standard Model and searches for New
Physics, and the determination of gamma and alpha from charmless hadronic B
decays.Comment: Invited plenary talk given at the 10th International Symposium on
Lepton and Photon Interactions at High Energies (Rome, Italy, 23-28 July
2001), 15 pages, 8 figure
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