1,975 research outputs found
Form factor in K+ --> pi+ pi0 gamma: interference versus direct emission
We analyze the effect of a form factor in the magnetic contribution to K+ -->
pi+ pi0 gamma. We emphasize how this can show up experimentally: in particular
we try to explore the difference between a possible interference contribution
and a form factor in the magnetic part. The form factor used for K+ --> pi+ pi0
gamma is analogous to the one for KL --> pi+ pi- gamma, experimentally well
established.Comment: 9 pages revtex, 10 eps figures; improved presentation of theoretical
and experimental status; refs. adde
Long-distance contribution to the forward-backward asymmetry in decays K+ --> pi+ l+ l-
The long-distance contribution via the two-photon intermediate state to the
forward-backward asymmetries in decays K+ --> pi+ l+ l- (l=e and mu) has been
studied within the standard model. In order to evaluate the dispersive part of
the K+ --> pi+ gamma* gamma* --> pi+ l+ l- amplitude, we employ a
phenomenological form factor to soften the ultraviolet behavior of the
transition. It is found that, this long-distance transition, although subject
to some theoretical uncertainties, can lead to significant contributions to the
forward-backward asymmetries, which could be tested in the future high-precise
experiments.Comment: 13 pages, 5 figure
K^+ -> pi^+pi^0e^+e^-: a novel short-distance probe
We study the decay K^+ -> pi^+ pi^0 e^+ e^-, currently under analysis by the
NA62 Collaboration at CERN. In particular, we provide a detailed analysis of
the Dalitz plot for the long-distance, gamma^*-mediated, contributions
(Bremsstrahlung, direct emission and its interference). We also examine a set
of asymmetries to isolate genuine short-distance effects. While we show that
charge asymmetries are not required to test short distances, they provide the
best environment for its detection. This constitutes by itself a strong
motivation for NA62 to study K^- decays in the future. We therefore provide a
detailed study of different charge asymmetries and the corresponding estimated
signals. Whenever possible, we make contact with the related processes K^+ ->
pi^+ pi^0 gamma and K_L -> pi^+ pi^- e^+ e^- and discuss the advantages of K^+
-> pi^+ pi^0 e^+ e^- over them.Comment: 25 pages, 6 figure
Kaon decays and the flavour problem
After a brief introduction to the so-called flavour problem, we discuss the
role of rare K decays in probing the mechanism of quark-flavour mixing.
Particular attention is devoted to the formulation of the Minimal Flavour
Violation hypothesis, as a general and natural solution to the flavour problem,
and to the fundamental role of K -> pi nu nu-bar decays in testing this
scenario.Comment: 10 pages, 6 figures, contribution to TH 2002 (Paris, July 2002
The s ---> d gamma decay in and beyond the Standard Model
The New Physics sensitivity of the s ---> d gamma transition and its
accessibility through hadronic processes are thoroughly investigated. Firstly,
the Standard Model predictions for the direct CP-violating observables in
radiative K decays are systematically improved. Besides, the magnetic
contribution to epsilon prime is estimated and found subleading, even in the
presence of New Physics, and a new strategy to resolve its electroweak versus
QCD penguin fraction is identified. Secondly, the signatures of a series of New
Physics scenarios, characterized as model-independently as possible in terms of
their underlying dynamics, are investigated by combining the information from
all the FCNC transitions in the s ---> d sector.Comment: 54 pages, 14 eps figure
Flavor Alignment via Shining in RS
We present a class of warped extra dimensional models whose flavor violating
interactions are much suppressed compared to the usual anarchic case due to
flavor alignment. Such suppression can be achieved in models where part of the
global flavor symmetry is gauged in the bulk and broken in a controlled manner.
We show that the bulk masses can be aligned with the down type Yukawa couplings
by an appropriate choice of bulk flavon field representations and TeV brane
dynamics. This alignment could reduce the flavor violating effects to levels
which allow for a Kaluza-Klein scale as low as 2-3 TeV, making the model
observable at the LHC. However, the up-type Yukawa couplings on the IR brane,
which are bounded from below by recent bounds on CP violation in the D system,
induce flavor misalignment radiatively. Off-diagonal down-type Yukawa couplings
and kinetic mixings for the down quarks are both consequences of this effect.
These radiative Yukawa corrections can be reduced by raising the flavon VEV on
the IR brane (at the price of some moderate tuning), or by extending the Higgs
sector. The flavor changing effects from the radiatively induced Yukawa mixing
terms are at around the current upper experimental bounds. We also show the
generic bounds on UV-brane induced flavor violating effects, and comment on
possible additional flavor violations from bulk flavor gauge bosons and the
bulk Yukawa scalars.Comment: 28 page
Iso-singlet Down Quark Mixing And CP Violation Experiments
We confront the new physics models with extra iso-singlet down quarks in the
new CP violation experimental era with and
measurements, events, and
limits. The closeness of the new experimental results to the standard
model theory requires us to include full SM amplitudes in the analysis. In
models allowing mixing to a new isosinglet down quark, as in E, flavor
changing neutral currents are induced that allow a mediated contribution
to mixing and which bring in new phases. In ,
, and plots we still find much
larger regions in the four down quark model than in the SM, reaching down to
, , , and down to zero, all at 1. We elucidate
the nature of the cancellation in an order four down quark mixing
matrix element which satisfies the experiments and reduces the number of
independent angles and phases. We also evaluate tests of unitarity for the
CKM submatrix.Comment: 14 pages, 16 figures, REVTeX
Chronic venous insufficiency strengthens the thrombo-embolic risk in congestive heart failure in elderly patients
A holographic approach to low-energy weak interactions of hadrons
We apply the double-trace formalism to incorporate nonleptonic weak
interactions of hadrons into holographic models of the strong interactions. We
focus our attention upon nonleptonic kaon decays. By working with
a Yang-Mills--Chern-Simons 5-dimensional action, we explicitly show how, at low
energies, one recovers the weak chiral Lagrangian for both the
anomalous and nonanomalous sectors. We provide definite predictions for the low
energy coefficients in terms of the AdS metric and argue that the double-trace
formalism is a 5-dimensional avatar of the Weak Deformation Model introduced
long ago by Ecker et al. As a significant phenomenological application, we
reassess the decays in the light of the holographic model. Previous
models found a fine-tuned cancellation of resonance exchange in these decays,
which was both conceptually puzzling and quantitatively in disagreement with
experimental results. The holographic model we build is an illustrative
counterexample showing that the cancellation encountered in the literature is
not generic but a model-dependent statement and that agreement with experiment
can be obtained.Comment: 20 page
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