4,385 research outputs found
Four-pion production in e+ e- annihilation
We calculate the processes e+ e- -> 4 pions and tau -> nu_tau + 4 pions to
O(p^4) in the low-energy expansion of the standard model. The chiral amplitudes
of O(p^4) can be extended via resonance exchange to energies around 1 GeV.
Higher-order effects have been included in the form of omega, a_1 and double
rho exchange and by performing a resummation of the pion form factor. The
predicted cross sections and the branching ratios BR(rho -> 4 pions) are in
good agreement with available data.Comment: 24 pages, 8 figures, small changes in the text, results and
conclusions unchanged, version to appear in EPJ
Four-pion production
Starting from the low-energy structure derived from QCD, we extend the
amplitudes for four-pion production in e+ e- annihilation and tau decays up to
invariant four-pion masses of 1 GeV. Cross sections and branching ratios
BR(rho^0 -> 4 pi) are compared with available data.Comment: 4 pages, 3 figures, contribution to Proc. of QCD'02, Montpellier,
July 2002, misprints correcte
Status of the KTeV Experiment at Fermilab
The KTeV experiment is a fixed target experiment at Fermilab. Its primary
goal is the search for direct CP violation in the decay of neutral kaons. Its
current status and some preliminary results will be discussed.Comment: 5 pages Latex, 4 figures; to be published in the proceedings of the
XVI International Workshop on Weak Interactions and Neutrinos, WIN '97,
Capri, Italy, June 22-28, 199
On the Corrections to Dashen's Theorem
The electromagnetic corrections to the masses of the pseudoscalar mesons
and are considered. We calculate in chiral perturbation theory the
contributions which arise from resonances within a photon loop at order . Within this approach we find rather moderate deviations to Dashen's
theorem.Comment: 14 pages, sligthly enlarged version; a numerical error is corrected
and the embedding of the figures is improved. The complete paper, including
figures, is also available via anonymous ftp at
ftp://www-ttp.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/; to be published in
Phys.Rev.
Power counting in baryon chiral perturbation theory including vector mesons
It is demonstrated that using a suitable renormalization condition one
obtains a consistent power counting in manifestly Lorentz-invariant baryon
chiral perturbation theory including vector mesons as explicit degrees of
freedom.Comment: 8 pages, REVTeX 4, 3 figure
Real CP violation in a simple extension of the standard model
I present a simple three-Higgs-doublet extension of the standard model in
which real CP violation takes place. The strong CP problem is attenuated by
this model.Comment: 8 page
Dispersion Relation Bounds for pi pi Scattering
Axiomatic principles such as analyticity, unitarity and crossing symmetry
constrain the second derivative of the pi pi scattering amplitudes in some
channels to be positive in a region of the Mandelstam plane. Since this region
lies in the domain of validity of chiral perturbation theory, we can use these
positivity conditions to bound linear combinations of \bar{l}_1 and \bar{l}_2.
We compare our predictions with those derived previously in the literature
using similar methods. We compute the one-loop pi pi scattering amplitude in
the linear sigma model (LSM) using the MS-bar scheme, a result hitherto absent
in the literature. The LSM values for \bar{l}_1 and \bar{l}_2 violate the
bounds for small values of m_sigma/m_pi. We show how this can occur, while
still being consistent with the axiomatic principles.Comment: 12 pages, 8 figures. Two references added, a few minor changes.
Published versio
Low Energy Constants from High Energy Theorems
New constraints on resonance saturation in chiral perturbation theory are
investigated. These constraints arise because each consistent saturation scheme
must map to a representation of the full QCD chiral symmetry group. The
low-energy constants of chiral perturbation theory are then related by a set of
mixing angles. It is shown that vector meson dominance is a consequence of the
fact that nature has chosen the lowest-dimensional nontrivial chiral
representation. It is further shown that chiral symmetry places an upper bound
on the mass of the lightest scalar in the hadron spectrum.Comment: 11 pages TeX and mtexsis.te
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Auxin-sensitive Aux/IAA proteins mediate drought tolerance in Arabidopsis by regulating glucosinolate levels.
A detailed understanding of abiotic stress tolerance in plants is essential to provide food security in the face of increasingly harsh climatic conditions. Glucosinolates (GLSs) are secondary metabolites found in the Brassicaceae that protect plants from herbivory and pathogen attack. Here we report that in Arabidopsis, aliphatic GLS levels are regulated by the auxin-sensitive Aux/IAA repressors IAA5, IAA6, and IAA19. These proteins act in a transcriptional cascade that maintains expression of GLS levels when plants are exposed to drought conditions. Loss of IAA5/6/19 results in reduced GLS levels and decreased drought tolerance. Further, we show that this phenotype is associated with a defect in stomatal regulation. Application of GLS to the iaa5,6,19 mutants restores stomatal regulation and normal drought tolerance. GLS action is dependent on the receptor kinase GHR1, suggesting that GLS may signal via reactive oxygen species. These results provide a novel connection between auxin signaling, GLS levels and drought response
FCNC in left-right symmetric theories and constraints on the right-handed scale
We revise the limits on the FCNC higgses in manifestly left-right symmetric
theories. It is shown that the combination of the Kobayashi-Maskawa
CP-violation with the tree level higgs exchange gives very large
contribution to the CP-violating parameter. It leads to the new
strong constraint on the FCNC higgs mass, M>50- 100 TeV, enhanced by factor of
the order . Being addressed to the supersymmetric left-right
models, FCNC problem requires both right-handed scale and supersymmetric mass
parameters be heavier than 50 TeV for . The most relaxed case
corresponds to where right-handed scale can be of the
order of few TeV.Comment: 11 pages, latex, 3 figure
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