3,549 research outputs found
Endpoint behavior of the pion distribution amplitude in QCD sum rules with nonlocal condensates
Starting from the QCD sum rules with nonlocal condensates for the pion
distribution amplitude, we derive another sum rule for its derivative and its
"integral" derivatives---defined in this work. We use this new sum rule to
analyze the fine details of the pion distribution amplitude in the endpoint
region . The results for endpoint-suppressed and flat-top (or
flat-like) pion distribution amplitudes are compared with those we obtained
with differential sum rules by employing two different models for the
distribution of vacuum-quark virtualities. We determine the range of values of
the derivatives of the pion distribution amplitude and show that
endpoint-suppressed distribution amplitudes lie within this range, while those
with endpoint enhancement---flat-type or CZ-like---yield values outside this
range.Comment: 20 pages, 10 figures, 1 table, conclusions update
Improved estimates of the pion-photon transition form factor in the ~GeV range and their theoretical uncertainties
We consider the pion-photon transition form factor at low to intermediate
spacelike momenta within the theoretical framework of light-cone sum rules. We
derive predictions which take into account all currently known contributions
stemming from QCD perturbation theory up to the next-to-next-to-leading order
(NNLO) and by including all twist terms up to order six. In order to enable a
more detailed comparison with forthcoming high-precision data, we also estimate
the main systematic theoretical uncertainties, stemming from various sources,
and discuss their influence on the calculations --- in particular the dominant
one related to the still uncalculated part of the NNLO contribution. The
analysis addresses, in broad terms, also the role of the twist-two pion
distribution amplitude derived with different approaches.Comment: 10 pages, 3 figures, Based on the talk given at the XIIth
International Conference "Quark Confinement and the Hadronic Spectrum"
(Thessaloniki, Greece, 28 August - 4 September 2016
Phenomenology of B -> pi pi, pi K Decays at O(alpha^2 beta_0) in QCD Factorization
We study O(alpha^2 beta_0) perturbative corrections to matrix elements
entering two-body exclusive decays of the form B -> pi pi, pi K in the QCD
factorization formalism, including chirally enhanced power corrections, and
discuss the effect of these corrections on direct CP asymmetries, which receive
their first contribution at O(alpha). We find that the O(alpha^2 beta_0)
corrections are often as large as the O(alpha) corrections. We find large
uncertainties due to renormalization scale dependence as well as poor knowledge
of the non-perturbative parameters. We assess the effect of the perturbative
corrections on the direct CP violation parameters of B -> pi^+ pi^-.Comment: 27 pages, 5 figures. Updated input parameters and added citations;
expanded discussio
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