Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: $B \to \pi\pi$ 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.

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The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
29
The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph