3,720 research outputs found
Absolutely stable proton and lowering the gauge unification scale
A unified model is constructed, based on flipped SU(5) in which the proton is absolutely stable. The model requires the existence of new leptons with masses of order the weak scale. The possibility that the unification scale could be extremely low is discussed
Kinetic mechanism of ornithine hydroxylase (PvdA) from Pseudomonas aeruginosa: substrate triggering of O2 addition but not flavin reduction
This publication was made possible by NIH Grant P20 RR-17708-05 from the National Center for Research Resources of the National Institutes of Health. K.M.M. was a recipient of a National Institutes of Health Predoctoral Training Grant Fellowship (GM08545).PvdA catalyzes the hydroxylation of the sidechain primary amine of ornithine in the initial step of the biosynthesis of the Pseudomonas aeruginosa siderophore pyoverdin. The reaction requires FAD, NADPH, and O2. PvdA uses the same co-substrates as several flavin-dependent hydroxylases that differ one from another in the kinetic mechanisms of their oxidative and reductive half-reactions. Therefore, the mechanism of PvdA was determined by absorption stopped-flow experiments. By contrast to some flavin-dependent hydroxylases (notably, p-hydroxybenzoate hydroxylase), binding of the hydroxylation target is not required to trigger reduction of the flavin by NADPH: the reductive half-reaction is equally facile in the presence and absence of ornithine. Reaction of O2 with FADH2 in the oxidative half-reaction is accelerated by ornithine 80-fold, providing a mechanism by which PvdA can ensure coupling of NADPH and ornithine oxidation. In the presence of ornithine, the expected C(4a)-hydroperoxyflavin intermediate with 390-nm absorption accumulates and decays to the C(4a)-hydroxyflavin in a kinetically competent fashion. The slower oxidative half-reaction that occurs in the absence of ornithine involves accumulation of an oxygenated flavin species and two subsequent states that are tentatively assigned as C(4a)-peroxy- and -hydroperoxyflavin intermediates and the oxidized flavin. The enzyme generates stoichiometric hydrogen peroxide in lieu of hydroxyornithine. The data suggest that PvdA employs a kinetic mechanism that is a hybrid of those previously documented for other flavin-dependent hydroxylases
A case report: Brugada syndrome in the setting of hypothermia.
Hypothermia is a common diagnosis in the Emergency Department. It can cause a multitude of symptoms and complications if not treated promptly. The following case report discusses Brugada pattern on an electrocardiogram in a patient with hypothermia and diabetic ketoacidosis. There was resolution of the Brugada pattern on the electrocardiogram after the patient was warmed to 35.3 °C
Lethal Mutagenesis of Picornaviruses with N-6-Modified Purine Nucleoside Analogues
RNA viruses exhibit extraordinarily high mutation rates during genome replication. Nonnatural ribonucleosides that can increase the mutation rate of RNA viruses by acting as ambiguous substrates during replication have been explored as antiviral agents acting through lethal mutagenesis. We have synthesized novel N-6-substituted purine analogues with ambiguous incorporation characteristics due to tautomerization of the nucleobase. The most potent of these analogues reduced the titer of poliovirus (PV) and coxsackievirus (CVB3) over 1,000-fold during a single passage in HeLa cell culture, with an increase in transition mutation frequency up to 65-fold. Kinetic analysis of incorporation by the PV polymerase indicated that these analogues were templated ambiguously with increased efficiency compared to the known mutagenic nucleoside ribavirin. Notably, these nucleosides were not efficient substrates for cellular ribonucleotide reductase in vitro, suggesting that conversion to the deoxyriboucleoside may be hindered, potentially limiting genetic damage to the host cell. Furthermore, a high-fidelity PV variant (G64S) displayed resistance to the antiviral effect and mutagenic potential of these analogues. These purine nucleoside analogues represent promising lead compounds in the development of clinically useful antiviral therapies based on the strategy of lethal mutagenesis
General Gauge and Anomaly Mediated Supersymmetry Breaking in Grand Unified Theories with Vector-Like Particles
In Grand Unified Theories (GUTs) from orbifold and various string
constructions the generic vector-like particles do not need to form complete
SU(5) or SO(10) representations. To realize them concretely, we present
orbifold SU(5) models, orbifold SO(10) models where the gauge symmetry can be
broken down to flipped SU(5) X U(1)_X or Pati-Salam SU(4)_C X SU(2)_L X SU(2)_R
gauge symmetries, and F-theory SU(5) models. Interestingly, these vector-like
particles can be at the TeV-scale so that the lightest CP-even Higgs boson mass
can be lifted, or play the messenger fields in the Gauge Mediated Supersymmetry
Breaking (GMSB). Considering GMSB, ultraviolet insensitive Anomaly Mediated
Supersymmetry Breaking (AMSB), and the deflected AMSB, we study the general
gaugino mass relations and their indices, which are valid from the GUT scale to
the electroweak scale at one loop, in the SU(5) models, the flipped SU(5) X
U(1)_X models, and the Pati-Salam SU(4)_C X SU(2)_L X SU(2)_R models. In the
deflected AMSB, we also define the new indices for the gaugino mass relations,
and calculate them as well. Using these gaugino mass relations and their
indices, we may probe the messenger fields at intermediate scale in the GMSB
and deflected AMSB, determine the supersymmetry breaking mediation mechanisms,
and distinguish the four-dimensional GUTs, orbifold GUTs, and F-theory GUTs.Comment: RevTex4, 45 pages, 15 tables, version to appear in JHE
Supersymmetric Monojets at the Large Hadron Collider
Supersymmetric monojets may be produced at the Large Hadron Collider by the
process qg -> squark neutralino_1 -> q neutralino_1 neutralino_1, leading to a
jet recoiling against missing transverse momentum. We discuss the feasibility
and utility of the supersymmetric monojet signal. In particular, we examine the
possible precision with which one can ascertain the neutralino_1-squark-quark
coupling via the rate for monojet events. Such a coupling contains information
on the composition of the neutralino_1 and helps bound dark matter direct
detection cross-sections and the dark matter relic density of the neutralino_1.
It also provides a check of the supersymmetric relation between gauge couplings
and gaugino-quark-squark couplings.Comment: 46 pages, 10 figures. The appendix has been rewritten to correct an
error that appears in all previous versions of the appendix. This error has
no effect on the results in the main body of the pape
Realistic Standard Model Fermion Mass Relations in Generalized Minimal Supergravity (GmSUGRA)
Grand Unified Theories (GUTs) usually predict wrong Standard Model (SM)
fermion mass relation m_e/m_{\mu} = m_d/m_s toward low energies. To solve this
problem, we consider the Generalized Minimal Supergravity (GmSUGRA) models,
which are GUTs with gravity mediated supersymmetry breaking and higher
dimensional operators. Introducing non-renormalizable terms in the super- and
K\"ahler potentials, we can obtain the correct SM fermion mass relations in the
SU(5) model with GUT Higgs fields in the {\bf 24} and {\bf 75} representations,
and in the SO(10) model. In the latter case the gauge symmetry is broken down
to SU(3)_C X SU(2)_L X SU(2)_R X U(1)_{B-L}, to flipped SU(5)X U(1)_X, or to
SU(3)_C X SU(2)_L X U(1)_1 X U(1)_2. Especially, for the first time we generate
the realistic SM fermion mass relation in GUTs by considering the
high-dimensional operators in the K\"ahler potential.Comment: JHEP style, 29 pages, no figure,references adde
A Two-Tiered Correlation of Dark Matter with Missing Transverse Energy: Reconstructing the Lightest Supersymmetric Particle Mass at the LHC
We suggest that non-trivial correlations between the dark matter particle
mass and collider based probes of missing transverse energy H_T^miss may
facilitate a two tiered approach to the initial discovery of supersymmetry and
the subsequent reconstruction of the LSP mass at the LHC. These correlations
are demonstrated via extensive Monte Carlo simulation of seventeen benchmark
models, each sampled at five distinct LHC center-of-mass beam energies,
spanning the parameter space of No-Scale F-SU(5).This construction is defined
in turn by the union of the Flipped SU(5) Grand Unified Theory, two pairs of
hypothetical TeV scale vector-like supersymmetric multiplets with origins in
F-theory, and the dynamically established boundary conditions of No-Scale
Supergravity. In addition, we consider a control sample comprised of a standard
minimal Supergravity benchmark point. Led by a striking similarity between the
H_T^miss distribution and the familiar power spectrum of a black body radiator
at various temperatures, we implement a broad empirical fit of our simulation
against a Poisson distribution ansatz. We advance the resulting fit as a
theoretical blueprint for deducing the mass of the LSP, utilizing only the
missing transverse energy in a statistical sampling of >= 9 jet events.
Cumulative uncertainties central to the method subsist at a satisfactory 12-15%
level. The fact that supersymmetric particle spectrum of No-Scale F-SU(5) has
thrived the withering onslaught of early LHC data that is steadily decimating
the Constrained Minimal Supersymmetric Standard Model and minimal Supergravity
parameter spaces is a prime motivation for augmenting more conventional LSP
search methodologies with the presently proposed alternative.Comment: JHEP version, 17 pages, 9 Figures, 2 Table
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