2,917 research outputs found
Radiative processes in external gravitational fields
Kinematically forbidden processes may be allowed in the presence of external
gravitational fields. These ca be taken into account by introducing generalized
particle momenta. The corresponding transition probabilities can then be
calculated to all orders in the metric deviation from the field-free
expressions by simply replacing the particle momenta with their generalized
counterparts. The procedure applies to particles of any spin and to any
gravitational fields. transition probabilities, emission power, and spectra
are, to leading order, linear in the metric deviation. It is also shown how a
small dissipation term in the particle wave equations can trigger a strong
backreaction that introduces resonances in the radiative process and deeply
affects the resulting gravitational background.Comment: 5 pages, 1 figur
Toll-like Receptor-4 Regulation of Hepatic Cyp3a11 Metabolism in a Mouse Model of LPS-induced CNS Inflammation
Central nervous system (CNS) infection and inflammation severely reduce the capacity of cytochrome P-450 metabolism in the liver. We developed a mouse model to examine the effects of CNS inflammation on hepatic cytochrome P-450 metabolism. FVB, C57BL/6, and C3H/HeouJ mice were given Escherichia coli LPS (2.5 μg) by intracerebroventricular (ICV) injection. The CNS inflammatory response was confirmed by the elevation of TNF-α and/or IL-1β proteins in the brain. In all mouse strains, LPS produced a 60–70% loss in hepatic Cyp3a11 expression and activity compared with saline-injected controls. Adrenalectomy did not prevent the loss in Cyp3a11 expression or activity, thereby precluding the involvement of the hypothalamic-adrenal-pituitary axis. Endotoxin was detectable (1–10 ng/ml) in serum between 15 and 120 min after ICV dosing of 2.5 μg LPS. Peripheral administration of 2.5 μg LPS by intraperitoneal injection produced similar serum endotoxin levels and a similar loss (60%) in Cyp3a11 expression and activity in the liver. The loss of Cyp3a11 in response to centrally or peripherally administered LPS could not be evoked in Toll-like receptor-4 (TLR4)-mutant (C3H/ HeJ) mice, indicating that TLR4 signaling pathways are directly involved in the enzyme loss. In summary, we conclude that LPS is transferred from the brain to the circulation in significant quantities in a model of CNS infection or inflammation. Subsequently, LPS that has reached the circulation stimulates a TLR4-dependent mechanism in the periphery, evoking a reduction in Cyp3a11 expression and metabolism in the liver
Neutrino Masses and Leptogenesis with Heavy Higgs Triplets
A simple and economical extension of the minimal standard electroweak gauge
model (without right-handed neutrinos) by the addition of two heavy Higgs
scalar triplets would have two significant advantages. \underline {Naturally}
small Majorana neutrino masses would become possible, as well as leptogenesis
in the early universe which gets converted at the electroweak phase transition
into the present observed baryon asymmetry.Comment: 12 pages including one figur
Report of the Working Group on `W Mass and QCD' (Phenomenology Workshop on LEP2 Physics, Oxford, April 1997)
The W Mass and QCD Working Group discussed a wide variety of topics relating
to present and future measurements of M(W) at LEP2, including QCD backgrounds
to W+W- production. Particular attention was focused on experimental issues
concerning the direct reconstruction and threshold mass measurements, and on
theoretical and experimental issues concerning the four jet final state. This
report summarises the main conclusions.Comment: 43 pages LaTeX and 15 encapsulated postscript figures. Uses epsfig
and ioplppt macros. Full Proceedings to be published in Journal of Physics
Meson Cloud of the Nucleon in Polarized Semi-Inclusive Deep-Inelastic Scattering
We investigate the possibility of identifying an explicit pionic component of
the nucleon through measurements of polarized baryon fragments
produced in deep-inelastic leptoproduction off polarized protons, which may
help to identify the physical mechanism responsible for the breaking of the
Gottfried sum rule. The pion-exchange model predicts highly correlated
polarizations of the and target proton, in marked contrast with
the competing diquark fragmentation process. Measurement of asymmetries in
polarized production may also reveal the presence of a kaon cloud in
the nucleon.Comment: 23 pages REVTeX, 7 uuencoded figures, accepted for publication in
Zeit. Phys.
in Symmetric Supersymmetry
We compute the one-loop corrections to the vertex in the
symmetric minimal supersymmetric extension of the standard model. We
find that the predicted value of is consistent with experiment if the
mass of the lighter top squark is no more than 180 GeV. Furthermore, other data
combines to place a lower bound of 88 GeV on the mass of the light top squark.
A top squark in this mass range should be accessible to searches by experiments
at FNAL and LEP.Comment: Corrected typos; added footnotes and a reference. 19 pages, LaTeX,
includes 8 figures, full postscript version at
http://smyrd.bu.edu/htfigs/htfigs.htm
A study of the nuclear medium influence on transverse momentum of hadrons produced in deep inelastic neutrino scattering
The influence of nuclear effects on the transverse momentum
distributions of neutrinoproduced hadrons is investigated using the data
obtained with SKAT propane-freon bubble chamber irradiated in the neutrino beam
(with = 3-30 GeV) at Serpukhov accelerator. Dependences of of hadrons (more pronounced for the
positively charged ones) produced in the target fragmentation region at low
invariant mass of the hadronic system (2 4 GeV) or at low energies
transferred to the current quark (2 GeV). At higher or ,
no influence of nuclear effects on is observed. Measurement results
are compared with predictions of a simple model, incorporating secondary
intranuclear interactions of hadrons (with a formation length extracted from
the Lund fragmentation model), which qualitatively reproduces the main features
of the data.Comment: 23 pages, 7 figure
PINK1 cleavage at position A103 by the mitochondrial protease PARL
Mutations in PTEN-induced kinase 1 (PINK1) cause early onset autosomal recessive Parkinson's disease (PD). PINK1 is a 63 kDa protein kinase, which exerts a neuroprotective function and is known to localize to mitochondria. Upon entry into the organelle, PINK1 is cleaved to produce a ∼53 kDa protein (ΔN-PINK1). In this paper, we show that PINK1 is cleaved between amino acids Ala-103 and Phe-104 to generate ΔN-PINK1. We demonstrate that a reduced ability to cleave PINK1, and the consequent accumulation of full-length protein, results in mitochondrial abnormalities reminiscent of those observed in PINK1 knockout cells, including disruption of the mitochondrial network and a reduction in mitochondrial mass. Notably, we assessed three N-terminal PD-associated PINK1 mutations located close to the cleavage site and, while these do not prevent PINK1 cleavage, they alter the ratio of full-length to ΔN-PINK1 protein in cells, resulting in an altered mitochondrial phenotype. Finally, we show that PINK1 interacts with the mitochondrial protease presenilin-associated rhomboid-like protein (PARL) and that loss of PARL results in aberrant PINK1 cleavage in mammalian cells. These combined results suggest that PINK1 cleavage is important for basal mitochondrial health and that PARL cleaves PINK1 to produce the ΔN-PINK1 fragment
MHV Rules for Higgs Plus Multi-Gluon Amplitudes
We use tree-level perturbation theory to show how non-supersymmetric one-loop
scattering amplitudes for a Higgs boson plus an arbitrary number of partons can
be constructed, in the limit of a heavy top quark, from a generalization of the
scalar graph approach of Cachazo, Svrcek and Witten. The Higgs boson couples to
gluons through a top quark loop which generates, for large top mass, a
dimension-5 operator H tr G^2. This effective interaction leads to amplitudes
which cannot be described by the standard MHV rules; for example, amplitudes
where all of the gluons have positive helicity. We split the effective
interaction into the sum of two terms, one holomorphic (selfdual) and one
anti-holomorphic (anti-selfdual). The holomorphic interactions give a new set
of MHV vertices -- identical in form to those of pure gauge theory, except for
momentum conservation -- that can be combined with pure gauge theory MHV
vertices to produce a tower of amplitudes with more than two negative
helicities. Similarly, the anti-holomorphic interactions give anti-MHV vertices
that can be combined with pure gauge theory anti-MHV vertices to produce a
tower of amplitudes with more than two positive helicities. A Higgs boson
amplitude is the sum of one MHV-tower amplitude and one anti-MHV-tower
amplitude. We present all MHV-tower amplitudes with up to four
negative-helicity gluons and any number of positive-helicity gluons (NNMHV).
These rules reproduce all of the available analytic formulae for Higgs +
n-gluon scattering (n<=5) at tree level, in some cases yielding considerably
shorter expressions.Comment: 34 pages, 8 figures; v2, references correcte
Representations of sport in the revolutionary socialist press in Britain, 1988–2012
This paper considers how sport presents a dualism to those on the far left of the political spectrum. A long-standing, passionate debate has existed on the contradictory role played by sport, polarised between those who reject it as a bourgeois capitalist plague and those who argue for its reclamation and reformation. A case study is offered of a political party that has consistently used revolutionary Marxism as the basis for its activity and how this party, the largest in Britain, addresses sport in its publications. The study draws on empirical data to illustrate this debate by reporting findings from three socialist publications. When sport did feature it was often in relation to high profile sporting events with a critical tone adopted and typically focused on issues of commodification, exploitation and alienation of athletes and supporters. However, readers’ letters, printed in the same publications, revealed how this interpretation was not universally accepted, thus illustrating the contradictory nature of sport for those on the far left
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