586 research outputs found

### Exclusive Charmless $B$ Decays in QCD

The problem of hadronic input in charmless nonleptonic B decays is discussed.
QCD sum rules and their light-cone versions (LCSR) provide an important part of
this input, such as the decay constant $f_B$ and $B\to \pi$ form factor.
Employing the LCSR technique, the $B\to \pi\pi$ hadronic matrix elements with
emission, penguin and annihilation topologies are calculated, with no evidence
for large nonfactorizable effects and/or strong phases.Comment: 6 pages, Invited talk at the First Workshop on Theory, Phenomenology
and Experiments in Heavy Flavour Physics, Anacapri, Italy, May 29-31 200

### Quantum Chromodynamics and Hadrons: an Elementary Introduction

Notes of five lectures given at the 2003 European School of High-Energy
Physics, Tsakhkadzor, Armenia, September 2003Comment: 52 pages, 25 figures, latex, cernrep.cls; lectures at the 2003
European School of High-Energy Physics, Tsakhkadzor, Armenia, September 200

### $B \to \pi\pi$ Decay in QCD

A new method is suggested to calculate the $B\to \pi\pi$ hadronic matrix
elements from QCD light-cone sum rules. To leading order in $\alpha_s$ and
$1/m_b$, the sum rule reproduces a factorizable matrix element, in accordance
with the prediction of the QCD factorization approach. Whereas the QCD
factorization can only take into account the nonfactorizable corrections
induced by hard-gluon exchanges, the method suggested here also allows a
systematic inclusion of soft-gluon effects. In this paper, I concentrate on the
latter aspect and present a calculation of the nonfactorizable soft-gluon
exchange contributions to $B\to \pi\pi$. The result, including twist 3 and 4
terms, is suppressed by one power of $1/m_b$ with respect to the factorizable
amplitude. Despite its numerical smallness, the soft effect is at the same
level as the $O(\alpha_s)$ correction to the QCD factorization formula for
$B\to \pi\pi$. The method suggested here can be applied to matrix elements of
different topologies and operators and to various other B-decay channels. I
also comment on the earlier applications of QCD sum rules to nonleptonic decays
of heavy mesons.Comment: 20 pages, 2 figures, Latex, epsfig.sty, a few sentences reworded, two
comments added, version to appear in Nucl. Phys.

### Applications of QCD Sum Rules to Heavy Quark Physics

In these lectures, I present several important applications of QCD sum rules
to the decay processes involving heavy-flavour hadrons. The first lecture is
introductory. As a study case, the sum rules for decay constants of the
heavy-light mesons are considered. They are relevant for the leptonic decays of
$B$-mesons. In the second lecture I describe the method of QCD light-cone sum
rules used to calculate the heavy-to-light form factors at large hadronic
recoil, such as the $B\to \pi \ell \nu_\ell$ form factors. In the third
lecture, the nonlocal hadronic amplitudes in the flavour-changing neutral
current decays $B\to K^{(*)}\ell\ell$ are discussed. Light-cone sum rules
provide important nonfactorizable contributions to these amplitudes.Comment: Lectures at the Helmholtz International Summer School "Physics of
Heavy Quarks and Hadrons'', July 2013, Dubna, Russia. SI-HEP-2013-1

### Counting contact terms in $B\to V\gamma$ decays

We clarify the origin and cancellation of contact terms in the weak
annihilation amplitudes contributing to $B\to V \gamma$. It is demonstrated
that the photon emission from the final-state quarks vanishes in the chiral
limit of massless quarks. The contact terms in the QCD light-cone sum rule
evaluation of the weak annihilation amplitudes are also discussed.Comment: 16 pages, 2 figures, Latex, ws-p8-50x6-00.cls, to be published in
Sergei Matinian Festschrift ``From Integrable Models to Gauge Theories.'',
Eds. V. Gurzadyan, A. Sedrakyan, World Scientific, 200

### Form factors in $B\to \pi\pi\ell\bar\nu_\ell$ from QCD light-cone sum rules

The form factors of the semileptonic $B\to \pi\pi\ell\bar\nu$ decay are
calculated from QCD light-cone sum rules with the distribution amplitudes of
dipion states. This method is valid in the kinematical region, where the
hadronic dipion state has a small invariant mass and simultaneously a large
recoil. The derivation of the sum rules is complicated by the presence of an
additional variable related to the angle between the two pions. In particular,
we realize that not all invariant amplitudes in the underlying correlation
function can be used, some of them generating kinematical singularities in the
dispersion relation. The two sum rules that are free from these ambiguities are
obtained in the leading twist-2 approximation, predicting the $\bar{B}^0\to
\pi^+\pi^0$ form factors $F_{\perp}$ and $F_{\parallel}$ of the vector and
axial $b\to u$ current, respectively. We calculate these form factors at the
momentum transfers $0<q^2\lesssim 12$ GeV$^2$ and at the dipion mass close to
the threshold $4m_\pi^2$. The sum rule results indicate that the contributions
of the higher partial waves to the form factors are suppressed with respect to
the lowest $P$-wave contribution and that the latter is not completely
saturated by the $\rho$-meson term.Comment: 17 pages, 4 figures, a few comments and references added, version to
be published in Nucl.Phys.

### QCD Sum Rules, a Modern Perspective

An introduction to the method of QCD sum rules is given for those who want to
learn how to use this method. Furthermore, we discuss various applications of
sum rules, from the determination of quark masses to the calculation of
hadronic form factors and structure functions. Finally, we explain the idea of
the light-cone sum rules and outline the recent development of this approach.Comment: 84 pages, 14 figures, Latex,epsfig,sprocl.sty. To be published in the
Boris Ioffe Festschrift ''At the Frontier of Particle Physics / Handbook of
QCD'', edited by M. Shifman (World Scientific, Singapore, 2001)

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