251 research outputs found
Renormalization of B-meson distribution amplitudes
We summarize a recent calculation of the evolution kernels of the
two-particle B-meson distribution amplitudes and taking into
account three-particle contributions. In addition to a few phenomenological
comments, we give as a new result the evolution kernel of the combination of
three-particle distribution amplitudes and confirm constraints
on and derived from the light-quark equation of motion.Comment: 7 pages, 2 figures. Contribution to the proceedings of the Int.
Workshop on Effective Field Theories: from the pion to the upsilon. Feb.
2009. Valencia, Spai
PoN-S : a systematic approach for applying the Physics of Notation (PoN)
Visual Modeling Languages (VMLs) are important instruments of communication between modelers and stakeholders. Thus, it is important to provide guidelines for designing VMLs. The most widespread approach for analyzing and designing concrete syntaxes for VMLs is the so-called Physics of Notation (PoN). PoN has been successfully applied in the analysis of several VMLs. However, despite its popularity, the application of PoN principles for designing VMLs has been limited. This paper presents a systematic approach for applying PoN in the design of the concrete syntax of VMLs. We propose here a design process establishing activities to be performed, their connection to PoN principles, as well as criteria for grouping PoN principles that guide this process. Moreover, we present a case study in which a visual notation for representing Ontology Pattern Languages is designed
Three-particle contributions to the renormalisation of B-meson light-cone distribution amplitudes
We study light-cone distribution amplitudes of heavy-light systems, such as a
B-meson. By an explicit computation, we determine how two-parton distribution
amplitudes mix with three-parton ones at one loop: \phi_+ is shown to mix only
into itself, whereas \phi_- mixes with the difference of three-parton
distribution amplitudes \Psi_A-\Psi_V. We determine the corresponding anomalous
dimension and we check the gauge independence of our result by considering a
general covariant gauge. Finally, we comment on some implications of our result
for phenomenological models of these distribution amplitudes.Comment: 21 pages, 5 figures, some comments and 2 references added, except for
typesetting matches version published in JHE
Resumming QCD vacuum fluctuations in three-flavour Chiral Perturbation Theory
Due to its light mass of order Lambda_QCD, the strange quark can play a
special role in Chiral Symmetry Breaking (ChSB): differences in the pattern of
ChSB in the limits N_f=2 (m_u,m_d->0, m_s physical) and N_f=3 (m_u,m_d,m_s->0)
may arise due to vacuum fluctuations of s-bar s pairs, related to the violation
of the Zweig rule in the scalar sector and encoded in particular in the O(p^4)
low-energy constants L_4 and L_6. In case of large fluctuations, we show that
the customary treatment of SU(3)xSU(3) chiral expansions generate instabilities
upsetting their convergence. We develop a systematic program to cure these
instabilities by resumming nonperturbatively vacuum fluctuations of s-bar s
pairs, in order to extract information about ChSB from experimental
observations even in the presence of large fluctuations. We advocate a Bayesian
framework for treating the uncertainties due to the higher orders. As an
application, we present a three-flavour analysis of the low-energy pi-pi
scattering and show that the recent experimental data imply a lower bound on
the quark mass ratio 2m_s/(m_u+m_d) > 14 at 95 % confidence level. We outline
how additional information may be incorporated to further constrain the pattern
of ChSB in the N_f=3 chiral limit.Comment: 58 pages, 8 figure
Convergence properties of decays in chiral perturbation theory
Theoretical efforts to describe and explain the decays reach
far back in time. Even today, the convergence of the decay widths and some of
the Dalitz plot parameters seems problematic in low energy QCD. In the
framework of resummed CHPT, we explore the question of compatibility of
experimental data with a reasonable convergence of a carefully defined chiral
series, where NNLO remainders are assumed to be small. By treating the
uncertainties in the higher orders statistically, we numerically generate a
large set of theoretical predictions, which are then confronted with
experimental information. In the case of the decay widths, the experimental
values can be reconstructed for a reasonable range of the free parameters and
thus no tension is observed, in spite of what some of the traditional
calculations suggest. The Dalitz plot parameters and can be described
very well too. When the parameters and are concerned, we find a
mild tension for the whole range of the free parameters, at less than 2
C.L. This can be interpreted in two ways - either some of the higher order
corrections are indeed unexpectedly large or there is a specific configuration
of the remainders, which is, however, not completely improbable. Also, the
distribution of the theoretical uncertainties is found to be significantly
non-gaussian, so the consistency cannot be simply judged by the 1 error
bars.Comment: 57 pages, 5 figure
Two-loop representations of low-energy pion form factors and pi-pi scattering phases in the presence of isospin breaking
Dispersive representations of the pi-pi scattering amplitudes and pion form
factors, valid at two-loop accuracy in the low-energy expansion, are
constructed in the presence of isospin-breaking effects induced by the
difference between the charged and neutral pion masses. Analytical expressions
for the corresponding phases of the scalar and vector pion form factors are
computed. It is shown that each of these phases consists of the sum of a
"universal" part and a form-factor dependent contribution. The first one is
entirely determined in terms of the pi-pi scattering amplitudes alone, and
reduces to the phase satisfying Watson's theorem in the isospin limit. The
second one can be sizeable, although it vanishes in the same limit. The
dependence of these isospin corrections with respect to the parameters of the
subthreshold expansion of the pi-pi amplitude is studied, and an equivalent
representation in terms of the S-wave scattering lengths is also briefly
presented and discussed. In addition, partially analytical expressions for the
two-loop form factors and pi-pi scattering amplitudes in the presence of
isospin breaking are provided.Comment: 57 pages, 12 figure
Implications from clean observables for the binned analysis of B -> K*ll at large recoil
We perform a frequentist analysis of q^2-dependent B-> K*(->Kpi)ll angular
observables at large recoil, aiming at bridging the gap between current
theoretical analyses and the actual experimental measurements. We focus on the
most appropriate set of observables to measure and on the role of the
q^2-binning. We highlight the importance of the observables P_i exhibiting a
limited sensitivity to soft form factors for the search for New Physics
contributions. We compute predictions for these binned observables in the
Standard Model, and we compare them with their experimental determination
extracted from recent LHCb data. Analyzing b->s and b->sll transitions within
four different New Physics scenarios, we identify several New Physics benchmark
points which can be discriminated through the measurement of P_i observables
with a fine q^2-binning. We emphasise the importance (and risks) of using
observables with (un)suppressed dependence on soft form factors for the search
of New Physics, which we illustrate by the different size of hadronic
uncertainties attached to two related observables (P_1 and S_3). We illustrate
how the q^2-dependent angular observables measured in several bins can help to
unravel New Physics contributions to B-> K*(->Kpi)ll, and show the
extraordinary constraining power that the clean observables will have in the
near future. We provide semi-numerical expressions for these observables as
functions of the relevant Wilson coefficients at the low scale.Comment: 50 pages, 21 figures. Improved form factor analysis, conclusions
unchanged. Plots with full resolution. Version published in JHE
Bs to l+ l- gamma as a Test of Lepton Flavor Universality
We discuss a number of strategies to reduce the theoretical error, and make such a measurement a new
probe of the interactions that are interesting in the light of present-day
flavor discrepancies. In particular, for low di-lepton invariant mass we
propose to exploit the close parenthood between and the measured . For high , conversely, we exploit the fact that the decay is
dominated by two form-factor combinations, plus contributions from broad
charmonium that we model accordingly. We construct the ratio , akin
to and likewise sensitive to lepton-universality violation. Provided the
two rates in this ratio are integrated in a suitable region that minimises
bremsstrahlung contributions while maximising statistics, the ratio is very
close to unity and the form-factor dependence cancels to an extent that makes
it a new valuable probe of lepton-universality violating contributions in the
effective Hamiltonian. We finally speculate on additional ideas to extract
short-distance information from resonance regions, which are theoretically
interesting but statistically limited at present.Comment: 21 pages, 4 figures. v4: in appendix removed equation already present
in main tex
Perturbative QCD Analysis of the Nucleon's Pauli Form Factor F_2(Q^2)
We perform a perturbative QCD analysis of the nucleon's Pauli form factor
in the asymptotically large limit. We find that the leading
contribution to has a power behavior, consistent with the
well-known result in the literature. Its coefficient depends on the leading-
and subleading-twist light-cone wave functions of the nucleon, the latter
describing the quarks with one unit of orbital angular momentum. We also derive
at the logarithmic accurary the asymptotic scaling which describes recent Jefferson Lab data well.Comment: 4 papes, 3 figures include
Consistent Analysis of the Transition Form Factor in the Whole Physical Region
In the paper, we show that the transition form factor can be
calculated by using the different approach in the different regions and
they are consistent with each other in the whole physical region. For the
transition form factor in the large recoil regions, one can apply the
PQCD approach, where the transverse momentum dependence for both the hard
scattering part and the non-perturbative wavefunction, the Sudakov effects and
the threshold effects are included to regulate the endpoint singularity and to
derive a more reliable PQCD result. Pionic twist-3 contributions are carefully
studied with a better endpoint behavior wavefunction for and we find
that its contribution is less than the leading twist contribution. Both the two
wavefunctions and of the B meson can give sizable
contributions to the transition form factor and should be kept for a
better understanding of the B decays. The present obtained PQCD results can
match with both the QCD light-cone sum rule results and the extrapolated
lattice QCD results in the large recoil regions.Comment: 18pages, 6 figure
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