217 research outputs found
Lepton Number Violating Radiative Decay in Models with R-parity Violation
Models with explicit R-parity violation can induce new rare radiative decay
modes of the boson into single supersymmetric particles which also violate
lepton number. We examine the rate and signature for one such decay,
, and find that such a mode will be very difficult
to observe, due its small branching fraction, even if the lepton number
violating coupling in the superpotential is comparable in strength to
electromagnetism. This parallels a similar result obtained earlier by Hewett in
the case of radiative decays.Comment: 10 pages, 2 figures(available on request), LaTex, ANL-HEP-PR-92-8
Caracterização dos agroecossistemas e manejo de germoplasma de Citrullus em três regiões do Nordeste brasileiro.
Sendo assim, este trabalho teve como objetivos caracterizar, estudar e descrever os agroecossistemas nordestinos representados pelos distritos de Jamarí-MA, Massaroca-BA e Urimamã-PE
Weissella halotolerans W22 combines arginine deiminase and ornithine decarboxylation pathways and converts arginine to putrescine
Aims: To demonstrate that the meat food strain Weissella halotolerans combines an ornithine decarboxylation pathway and an arginine deiminase (ADI) pathway and is able to produce putrescine, a biogenic amine. Evidence is shown that these two pathways produce a proton motive force (PMF). Methods and Results: Internal pH in W. halotolerans was measured with the sensitive probe 2',7'-bis-(2-carboxyethyl)-5(and-6)-carboxyfluorescein. Membrane potential was measured with the fluorescent probe 3,3'-dipropylthiocarbocyanine iodine. Arginine and ornithine transport studies were made under several conditions, using cells loaded or not loaded with the biogenic amine putrescine. ADI pathway caused an increase in Delta pH dependent on the activity of F(0)F(1)ATPase. Ornithine decarboxylation pathway generates both a Delta pH and a Delta Psi. Both these pathways lead to the generation of a PMF. Conclusions: Weissella halotolerans W22 combines an ADI pathway and an ornithine decarboxylation pathway, conducing to the production of the biogenic amine putrescine and of a PMF. Transport studies suggest the existence of a unique antiporter arginine/putrescine in this lactic acid bacteria strain. Significance and Impact of the Study: The coexistence of two different types of amino acid catabolic pathways, leading to the formation of a PMF, is shown for a Weissella strain for the first time. Moreover, a unique antiport arginine/putrescine is hypothesized to be present in this food strain
A Supersymmetric Solution to the Solar and Atmospheric Neutrino Problems
The simplest unified extension of the Minimal Supersymmetric Standard Model
with bi-linear R--Parity violation provides a predictive scheme for neutrino
masses which can account for the observed atmospheric and solar neutrino
anomalies in terms of bi-maximal neutrino mixing. The maximality of the
atmospheric mixing angle arises dynamically, by minimizing the scalar
potential, while the solar neutrino problem can be accounted for either by
large or by small mixing oscillations. One neutrino picks up mass by mixing
with neutralinos, while the degeneracy and masslessness of the other two is
lifted only by loop corrections. Despite the smallness of neutrino masses
R-parity violation is observable at present and future high-energy colliders,
providing an unambiguous cross-check of the model.Comment: 5 pages, final version published in Phys. Rev. D61, 2000, 071703(R
Reductive activation and structural rearrangement in superoxide reductase: a combined infrared spectroscopic and computational study
Superoxide reductases (SOR) are a family of non-heme iron enzymes that limit oxidative stress by catalysing the reduction of superoxide to hydrogen peroxide and, thus, represent model systems for the detoxification of reactive oxygen species. In several enzymes of this type, reductive activation of the active site involves the reversible dissociation of a glutamate from the proposed substrate binding site at the iron. In this study we have employed IR spectroscopic and theoretical methods to gain insights into redox-linked structural changes of 1Fe-type superoxide reductases, focusing on the enzyme from the archaeon Ignicoccus hospitalis. Guided by crystal structure data and complemented by spectra calculation for an active site model, the main IR difference signals could be assigned. These signals reflect redox-induced structural changes in the first coordination sphere of the iron centre, adjacent loop and helical regions, and more remote β-sheets. By comparison with the spectra obtained for the E23A mutant of Ignicoccus hospitalis SOR, it is shown that glutamate E23 dissociates reversibly from the ferrous iron during reductive activation of the wild type enzyme. Moreover, this process is found to trigger a global conformational transition of the protein that is strictly dependent on the presence of E23. Similar concerted structural changes can be inferred from the IR spectra of related SORs such as that from Archaeoglobus fulgidus, indicating a widespread mechanism. A possible functional role of this process in terms of synergistic effects during reductive activation of the homotetrameric enzyme is proposed.DFG, EXC 314, Unifying Concepts in Catalysi
Broken R-parity, stop decays, and neutrino physics
We discuss the phenomenology of the lightest stop in models where R-parity is
broken by bilinear superpotential terms. In this class of models we consider
scenarios where the R-parity breaking two-body decay ~t_1->\tau^+b competes
with the leading three-body decays such as ~t_1->W^+b~\chi^0_1. We demonstrate
that the R-parity violating decay can be sizable and in some parts of the
parameter space even the dominant one. Moreover we discuss the expectations for
\~t_1->\mu^+b and ~t_1->e^+b. The recent results from solar and atmospheric
neutrinos suggest that these are as important as the tau bottom mode. The
\~t_1->l^+b decays are of particular interest for hadron colliders, as they may
allow a full mass reconstruction of the lighter stop. Moreover these decay
modes allow cross checks on the neutrino mixing angle involved in the solar
neutrino puzzle complementary to those possible using neutralino decays. For
the so--called small mixing angle or SMA solution ~t_1->e^+b should be
negligible, while for the large mixing angle type solutions all ~t_1->l^+b
decays should have comparable magnitude.Comment: 51 pages, 6 figures, LaTeX2e and RevTeX4, published versio
Leptonic CP Violation in Supersymmetric Standard Model
We point out the possibility of spontaneous and hard CP-violation in the
scalar potential of R-parity broken supersymmetric Standard Model. The
existence of spontaneous CP-violation depends crucially on the R-parity
breaking terms in the superpotential and, in addition, on the choice of the
soft supersymmetry breaking terms. Unlike in theories with R-parity
conservation, it is natural, in the context of the present model, for the
sneutrinos to acquire (complex) vacuum expectation values. In the context of
this model we examine here the global implications, like the strength of the
CP-violating interactions and the neutrino masses.Comment: REVTEX, 15 page
Supersymmetric Origin of Neutrino Mass
Supersymmetry with breaking of R-parity provides an attractive way to
generate neutrino masses and lepton mixing angles in accordance to present
neutrino data. We review the main theoretical features of the bilinear R-parity
breaking (BRpV) model, and stress that it is the simplest extension of the
minimal supersymmetric standard model (MSSM) which includes lepton number
violation. We describe how it leads to a successful phenomenological model with
hierarchical neutrino masses. In contrast to seesaw models, the BRpV model can
be probed at future collider experiments, like the Large Hadron Collider or the
Next Linear Collider, since the decay pattern of the lightest supersymmetric
particle provides a direct connection with the lepton mixing angles determined
by neutrino experiments.Comment: 21 pages, 8 figures, review for NJP focus issue on neutrino
On the Size of the Dark Side of the Solar Neutrino Parameter Space
We present an analysis of the MSW neutrino oscillation solutions of the solar
neutrino problem in the framework of two-neutrino mixing in the enlarged
parameter space with . Recently, it was pointed out that the allowed region of
parameters from a fit to the measured total rates can extend to values (the so called ``dark side'') when higher confidence levels
are allowed. The purpose of this letter is to reanalize the problem including
all the solar neutrino data available, to discuss the dependence on the
statistical criteria in the determination of the CL of the ``dark side'' and to
extract the corresponding limits on the largest mixing allowed by the data. Our
results show that when the Super-Kamiokande data on the zenith angle
distribution of events and the spectrum information is included, the regions
extend more into the dark side.Comment: 5 pages,latex file using RevTex. Two-layer aproximation for the Earth
density replaced by numerical integration with PREM. Latest parametrization
of the sun matter density (BP2000) is included. Misprints corrected.
Conclusions unchanged. 5 postscript figures (bitmapped for compression). A
full version of the paper can be found at http://ific.uv.es/~penya/papers/ To
appear in Phys. Rev.
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