3,784 research outputs found
Mixing and Decay Constants of Pseudoscalar Mesons: The Sequel
We present further tests and applications of the new eta-eta' mixing scheme
recently proposed by us. The particle states are decomposed into orthonormal
basis vectors in a light-cone Fock representation. Because of flavor symmetry
breaking the mixing of the decay constants can be identical to the mixing of
particle states at most for a specific choice of this basis. Theoretical and
phenomenological considerations show that the quark flavor basis has this
property and allows, therefore, for a reduction of the number of mixing
parameters. A detailed comparison with other mixing schemes is also presented.Comment: 9 page
Neutrino-Mass Hierarchies and Non-linear Representation of Lepton-Flavour Symmetry
Lepton-flavour symmetry in the Standard Model is broken by small masses for
charged leptons and neutrinos. Introducing neutrino masses via dimension-5
operators associated to lepton-number violation at a very high scale, the
corresponding coupling matrix may still have entries of order 1, resembling the
situation in the quark sector with large top Yukawa coupling. As we have shown
recently, in such a situation one may introduce the coupling matrices between
lepton and Higgs fields as non-linear representations of lepton-flavour
symmetry within an effective-theory framework. This allows us to separate the
effects related to the large mass difference observed in atmospheric neutrino
oscillations from those related to the solar mass difference. We discuss the
cases of normal or inverted hierarchical and almost degenerate neutrino
spectrum, give some examples to illustrate minimal lepton-flavour violation in
radiative and leptonic decays, and also provide a systematic definition of
next-to-minimal lepton-flavour violation within the non-linear framework.Comment: 17 pages, 1 figur
Factorization in B -> K pi e+e- decays
We derive factorization relations for the transverse helicity amplitudes in
the rare decays B-> K\pi l+l- at leading order in Lambda/m_b, in the
kinematical region with an energetic kaon and a soft pion. We identify and
compute a new contribution of leading order in Lambda/m_b to the B->K\pi l+l-
amplitude, which is not present in the one-body decay B-> K*l+l-. As an
application we study the forward-backward asymmetry (FBA) of the lepton
momentum angular distribution in B-> K\pi l+l- decays away from the K*
resonance. The FBA in these decays has a zero at q0^2 = q0^2(M_{Kpi}), which
can be used, in principle, for determining the Wilson coefficients C_{7,9} and
testing the Standard Model. We point out that the slope of the q0^2(M_{Kpi}^2)
curve contains the same information about the Wilson coefficients as the
location of the zero, but is less sensitive to unknown nonperturbative
dynamics. We estimate the location of the zero at leading order in
factorization, and using a resonant model for the B -> K\pi l+l-
nonfactorizable amplitude.Comment: 16 pages, 5 figures. Version to appear in Physical Review D. One new
observable introduced and considered - the slope of the zero of the
forward-backward asymmetry as function of the K\pi invariant mas
See-Saw Masses for Quarks and Leptons in SU(5)
We build on a recent paper by Grinstein, Redi and Villadoro, where a see-saw
like mechanism for quark masses was derived in the context of spontaneously
broken gauged flavour symmetries. The see-saw mechanism is induced by heavy
Dirac fermions which are added to the Standard Model spectrum in order to
render the flavour symmetries anomaly-free. In this letter we report on the
embedding of these fermions into multiplets of an SU(5) grand unified theory
and discuss a number of interesting consequences.Comment: 15 pages, 4 figures (v3: outline restructured, modified mechanism to
cancel anomalies
Factorization in exclusive semileptonic radiative B decays
We derive a new factorization relation for the semileptonic radiative decay B
-> \pi \ell \nu \gamma in the kinematical region of a slow pion p_\pi ~ \Lambda
and an energetic photon E_\gamma >> \Lambda, working at leading order in
\Lambda/m_b. In the limit of a soft pion, the nonperturbative matrix element
appearing in this relation can be computed using chiral perturbation theory. We
present a phenomenological study of this decay, which may be important for a
precise determination of the exclusive nonradiative decay.Comment: 10 pages, 3 figures; minor corrections, one reference adde
The decay pi0 to gamma gamma to next to leading order in Chiral Perturbation Theory
The two photon decay width of the neutral pion is analyzed within the
combined framework of Chiral Perturbation Theory and the 1/Nc expansion up to
order p^6 and p^4 times 1/Nc in the decay amplitude. The eta' is explicitly
included in the analysis. It is found that the decay width is enhanced by about
4.5% due to the isospin-breaking induced mixing of the pure U(3) states. This
effect, which is of leading order in the low energy expansion, is shown to
persist nearly unchanged at next to leading order. The chief prediction for the
width with its estimated uncertainty is 8.10+-0.08 eV. This prediction at the
1% level makes the upcomming precision measurement of the decay width even more
urgent.
Observations on the eta and eta' can also be made, especially about their
mixing, which is shown to be significantly affected by next to leading order
corrections.Comment: 21 pages, two figure
Charmless Two-body decays In Soft-Collinear-Effective-Theory
We provide the analysis of charmless two-body decays under the
framework of the soft-collinear-effective-theory (SCET), where denotes a
light vector (pseudoscalar) meson. Besides the leading power contributions,
some power corrections (chiraly enhanced penguins) are also taken into account.
Using the current available and experimental data on
branching fractions and CP asymmetry variables, we find two kinds of solutions
in fit for the 16 non-perturbative inputs which are essential in the
87 and decay channels. Chiraly enhanced penguins can change
several charming penguins sizably, since they share the same topology. However,
most of the other non-perturbative inputs and predictions on branching ratios
and CP asymmetries are not changed too much. With the two sets of inputs, we
predict the branching fractions and CP asymmetries of other modes especially
decays. The agreements and differences with results in QCD
factorization and perturbative QCD approach are analyzed. We also study the
time-dependent CP asymmetries in channels with CP eigenstates in the final
states and some other channels such as and
. In the perturbative QCD approach, the
penguins in annihilation diagrams play an important role. Although
they have the same topology with charming penguins in SCET, there are many
differences between the two objects in weak phases, magnitudes, strong phases
and factorization properties.Comment: 34 pages, revtex, 2 figures, published at PR
Branching ratios and CP asymmetries of decays in the pQCD approach
We calculate the branching ratios and CP violating asymmetries of the four B
\to K \etap decays in the perturbative QCD (pQCD) factorization approach.
Besides the full leading order contributions, the partial next-to-leading order
(NLO) contributions from the QCD vertex corrections, the quark loops, and the
chromo-magnetic penguins are also taken into account. The NLO pQCD predictions
for the CP-averaged branching ratios are , Br(B^\pm \to K^\pm \etar) \approx 51.0 \times 10^{-6},
, and Br(B^0 \to K^0 \etar)
\approx 50.3 \times 10^{-6}. The NLO contributions can provide a 70%
enhancement to the LO Br(B \to K \etar), but a 30% reduction to the LO , which play the key role in understanding the observed pattern of
branching ratios. The NLO pQCD predictions for the CP-violating asymmetries,
such as \acp^{dir} (K^0_S \etar) \sim 2.3% and \acp^{mix}(K^0_S \etar)\sim
63%, agree very well with currently available data. This means that the
deviation \Delta S=\acp^{mix}(K^0_S \etar) - \sin{2\beta} in pQCD approach is
also very small.Comment: 31 pages, 11 ps/eps figures, typos corrected. A little modificatio
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