12,114 research outputs found

### QCD Sum Rule Analysis of the Subleading Isgur-Wise Form Factor $\chi_2(v\cdot v')$

We present a QCD sum rule calculation of the spin-symmetry violating
universal function $\chi_2(v\cdot v')$, which appears at order $1/m_Q$ 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 $\alpha_s$ is evaluated. In
particular, we find $\chi_2(1) = -(3.8\pm 0.4)\%$ at zero recoil, indicating
that $1/m_Q$ 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

### QCD Sum-Rule Calculation of the Kinetic Energy and Chromo-Interaction of Heavy Quarks Inside Mesons

We present a QCD sum-rule determination of the heavy-quark kinetic energy
inside a heavy meson, $-\lambda_1/2 m_Q$, which is consistent with the
field-theory analog of the virial theorem. We obtain -\lambda_1\approx
(0.10\pm 0.05)~\mbox{GeV}^2, significantly smaller than a previous sum-rule
result, but in good agreement with recent determinations from the analysis of
inclusive decays. We also present a new determination of the chromo-magnetic
interaction, yielding \lambda_2(m_b)=(0.15\pm 0.03)~\mbox{GeV}^2. This
implies m_{B^*}^2-m_B^2=(0.60\pm 0.12)~\mbox{GeV}^2, in good agreement with
experiment. As a by-product of our analysis, we derive the QCD sum rules for
the three form factors describing the meson matrix element of a
velocity-changing current operator containing the gluon field-strength tensor.Comment: 13 pages LaTeX (A4), 3 figure

### Uncertainties in the Determination of $|V_{cb}|$

I discuss the theoretical uncertainties in the extraction of $|\,V_{cb}|$
from semilep\-to\-nic decays of $B$ mesons, taking into account the most recent
theoretical developments. The main sources of uncertainty are identified both
for the exclusive decay mode $B\to D^*\ell\,\bar\nu$ and for the inclusive
channel $B\to X\,\ell\,\bar\nu$. From an analysis of the available experimental
data, I obtain $|\,V_{cb}|_{\rm excl} = 0.041\pm 0.003_{\rm exp}\pm 0.002_{\rm
th}$ from the exclusive mode, and $|\,V_{cb}|_{\rm incl} = 0.040\pm 0.001_{\rm
exp}\pm 0.005_{\rm th}$ from the inclusive mode. I also give a prediction for
the slope of the form factor ${\cal{F}}(w)$ at zero recoil, which is
$\widehat\varrho^2=0.8\pm 0.3$.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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