12,152 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
Uncertainties in the Determination of
I discuss the theoretical uncertainties in the extraction of
from semilep\-to\-nic decays of mesons, taking into account the most recent
theoretical developments. The main sources of uncertainty are identified both
for the exclusive decay mode and for the inclusive
channel . From an analysis of the available experimental
data, I obtain from the exclusive mode, and from the inclusive mode. I also give a prediction for
the slope of the form factor at zero recoil, which is
.Comment: Proceedings of 1995 Moriond Conference on Electroweak Interactions
and Unified Theories, 11 pages, 3 figures available as uu-encoded postscript
file
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