4,830 research outputs found
Mobile Payments for Remittances in Latin America: Benchmarking with Africa
Rücküberweisung (Migranten); Bargeldloser Zahlungsverkehr; Mobiltelefon; Transaktionskosten; Vergleich; Lateinamerika; Afrika
Mobile payments for remittances in Africa: Benchmarking with Latin America
In this article the author seeks to explain the reasons backing the success of mobile technology in money transfers comparing Africa and Latin America.Remittances, Africa, Latin America, mobile phones
Time dependence in decays
We discuss the theory and phenomenology of
decays in the presence of neutral-meson mixing. We derive expressions for the
time-dependent angular distributions for decays into CP eigenstates, and
identify the relevant observables that can be extracted from time-integrated
and time-dependent analyses with or without tagging, with a focus on the
difference between measurements at -factories and hadronic machines. We
construct two observables of interest, which we call and , and
which are theoretically clean at large recoil. We compute these two observables
in the Standard Model, and show that they have good potential for New Physics
searches by considering their sensitivity to benchmark New Physics scenarios
consistent with current data. These results apply to decays
such as ,
and .Comment: 39 pages, 3 figures. Typos corrected. Matches published versio
Four-body contributions to B -> Xs gamma at NLO
Ongoing efforts to reduce the perturbative uncertainty in the B -> Xs gamma
decay rate have resulted in a theory estimate to NNLO in QCD. However, a few
contributions from multi-parton final states which are formally NLO are still
unknown. These are parametrically small and included in the estimated error
from higher order corrections, but must be computed if one is to claim complete
knowledge of the B -> Xs gamma rate to NLO. A major part of these unknown
pieces are four-body contributions corresponding to the partonic process b -> s
qbar q gamma. We compute these NLO four-body contributions to B -> Xs gamma,
and confirm the corresponding tree-level leading-order results. While the NLO
contributions arise from tree-level and one-loop Feynman diagrams, the
four-body phase-space integrations make the computation non-trivial. The decay
rate contains collinear logarithms arising from the mass regularization of
collinear divergences. We perform an exhaustive numerical analysis, and find
that these contributions are positive and amount to no more than 1% of the
total rate in the Standard Model, thus confirming previous estimates of the
perturbative uncertainty.Comment: 37 pages, 8 figure
Timelike-helicity form factor from light-cone sum rules with dipion distribution amplitudes
We complete the set of QCD light-cone sum rules for transition
form factors, deriving a new sum rule for the timelike-helicity form factor
in terms of dipion distribution amplitudes. This sum rule, in the leading
twist-2 approximation, is directly related to the pion vector form factor.
Employing a relation between and other form factors we
obtain also the longitudinal-helicity form factor . In this way, all four
(axial-)vector form factors are predicted from light-cone sum
rules with dipion distribution amplitudes. These results are valid for small
dipion masses with large momentum.Comment: 7 pages, 3 figure
Three-Body Non-Leptonic B Decays and QCD Factorization
We extend the framework of QCD factorization to non-leptonic decays into
three light mesons, taking as an example the decay .
We discuss the factorization properties of this decay in different regions of
phase space. We argue that, in the limit of very large -quark mass, the
central region of the Dalitz plot can be described in terms of the
form factor and the and light-cone distribution amplitudes. The edges
of the Dalitz plot, on the other hand, require different non-perturbative
input: the form factor and the two-pion distribution amplitude.
We present the set-up for both regions to leading order in both and
and discuss how well the two descriptions merge. We
argue that for realistic -meson masses there is no perturbative center in
the Dalitz plot, but that a systematic description might be possible in the
context of two-pion states. As an example, we estimate the
branching fraction beyond the quasi-particle approximation. We also discuss the
prospects for studies of three-body and quasi-two-body non-leptonic decays
from QCD.Comment: 20 pages, 8 figures. Version published in Nucl.Phys.
Form Factors from Light-Cone Sum Rules with -meson Distribution Amplitudes
We study form factors using QCD light-cone sum rules with
-meson distribution amplitudes. These form factors describe the semileptonic
decay , and constitute an essential input in
and decays. We employ the
correlation functions where a dipion isospin-one state is interpolated by the
vector light-quark current. We obtain sum rules where convolutions of the
-wave form factors with the time-like pion vector
form factor are related to universal -meson distribution amplitudes. These
sum rules are valid in the kinematic regime where the dipion state has a large
energy and a low invariant mass, and reproduce analytically the known
light-cone sum rules for form factors in the limit of
-dominance with zero width, thus providing a systematics for
so-far-unaccounted corrections to transitions. Using data for the
pion vector form factor, we estimate finite width-effects and the contribution
of excited -resonances to the form factors. We find that
these contributions amount up to in the small dipion mass region
where they can be effectively regarded as a nonresonant (-wave) background
to the transition.Comment: 28 pages, 3 figures. A few comments added. Version published in JHE
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