2,190 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
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
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
The hadronic light by light contribution to the with holographic models of QCD
We study the anomalous electromagnetic pion form factor
with a set of holographic models. By comparing with
the measured value of the linear slope, some of these models can be ruled out.
From the remaining models we obtain predictions for the low-energy quadratic
slope parameters of , currently out of experimental
reach but testable in the near future. We find it particularly useful to encode
this low-energy information in a form factor able to satisfy also QCD
short-distance constraints. We choose the form factor introduced by D'Ambrosio,
Isidori and Portoles in kaon decays, which has the right short distance for a
particular value of the quadratic slope, which is later shown to be compatible
with our holographic predictions. We then turn to a determination of the
(dominant) pion exchange diagram in the hadronic light by light scattering
contribution to the muon anomalous magnetic moment. We quantify the theoretical
uncertainty in coming from the different input we use: QCD short
distances, experimental input and low-energy holographic predictions. We also
test the pion-pole approximation. Our final result is
, where the error is driven by the
linear slope of , soon to be measured with precision
at KLOE-2. Our numerical analysis also indicates that large values of the
magnetic susceptibility are disfavored, therefore pointing at a mild
effect from the pion off-shellness. However, in the absence of stronger bounds
on , an additional systematic uncertainty on the previous
value for cannot be excluded.Comment: 20 pages, 5 figures. Substantial improvements throughout the text to
match the published version. Enhanced discussion of the analysis in Section
IV with the addition of two appendices. Conclusions unchange
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
Recommended from our members
Dynamics of Post-Injection Fuel Flow in Mini-Sac Diesel Injectors Part 1: Admission of 1 External Gases and Implications for Deposit Formation
Samples of unadditized, middle distillate diesel fuel were injected through real-size optically accessible mini-sac diesel injectors into ambient air at common rail pressures of 250 bar and 350 bar respectively. High-resolution images of white light scattered from the internal mini-sac and nozzle flow were captured on a high-speed monochrome video camera. Following the end of each injection, the momentum-driven evacuation of fuel liquid from the mini-sac and nozzle holes resulted in the formation of a vapour cloud and bubbles in the mini-sac, and vapour capsules in the nozzle holes. This permitted external gas to gain entrance to the nozzle holes.
The diesel fuel in the mini-sac was observed to rotate with large initial vorticity, which decayed until the fuel became stationary. The diesel fuel remaining in the nozzle holes was observed to move inwards towards the mini-sac or outwards towards the nozzle exit in concert with the rotational flow in the mini-sac. The mini-sac bubbles’ internal pressure differences revealed that the bubbles must have contained previously dissolved oxygen and nitrogen. Under diesel engine operating conditions, this multi-phase mixture would be highly reactive and could initiate local pyrolysis and/or oxidation reactions. Finally, the dynamical behaviour of the diesel fuel in the nozzle holes would support the admission of external hot combustion gases into the nozzle holes, establishing the conditions for oxidation/pyrolysis reactions with surrounding liquid fuel films
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
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
Localization and bioreactivity of cysteine-rich secretions in the marine gastropod nucella lapillus
PTDC/BTA-BTA/28650/2017 FA_05_2017_007). The Applied Molecular Biosciences Unit (UCIBIO) is financed by national funds from FCT, UID/Multi/04378/2020. FCT is also acknowledged for the grant SFRH/BD/144914/2019 to C.G. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Marine biodiversity has been yielding promising novel bioproducts from venomous animals. Despite the auspices of conotoxins, which originated the paradigmatic painkiller Prialt, the biotechnological potential of gastropod venoms remains to be explored. Marine bioprospecting is expanding towards temperate species like the dogwhelk Nucella lapillus, which is suspected to secrete immobilizing agents through its salivary glands with a relaxing effect on the musculature of its preferential prey, Mytilus sp. This work focused on detecting, localizing, and testing the bioreactivity of cysteine-rich proteins and peptides, whose presence is a signature of animal venoms and poisons. The highest content of thiols was found in crude protein extracts from the digestive gland, which is associated with digestion, followed by the peribuccal mass, where the salivary glands are located. Conversely, the foot and siphon (which the gastropod uses for feeding) are not the main organs involved in toxin secretion. Ex vivo bioassays with Mytilus gill tissue disclosed the differential bioreactivity of crude protein extracts. Secretions from the digestive gland and peribuccal mass caused the most significant molecular damage, with evidence for the induction of apoptosis. These early findings indicate that salivary glands are a promising target for the extraction and characterization of bioactive cysteine-rich proteinaceous toxins from the species.publishersversionpublishe
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