956 research outputs found
Axion Dissipation Through the Mixing of Goldstone Bosons
By coupling axions strongly to a hidden sector, the energy density in
coherent axions may be converted to radiative degrees of freedom, alleviating
the ``axion energy crisis''. The strong coupling is achieved by mixing the
axion and some other Goldstone boson through their kinetic energy terms, in a
manner reminiscent of paraphoton models. Even with the strong coupling it
proves difficult to relax the axion energy density through particle absorption,
due to the derivative nature of Goldstone boson couplings and the effect of
back reactions on the evolution of the axion number density. However, the
distribution of other particle species in the hidden sector will be driven from
equilibrium by the axion field oscillations. Restoration of thermal equilibrium
results in energy being transferred from the axions to massless particles,
where it can redshift harmlessly without causing any cosmological problems.Comment: 20 pages, Latex, (3 uuencoded compressed tarred postscript figures
attached
Intranasal Resveratrol Nanoparticles Enhance Neuroprotection in a Model of Multiple Sclerosis.
Resveratrol is a natural polyphenol which has a very low bioavailability but whose antioxidant, anti-inflammatory and anti-apoptotic properties may have therapeutic potential for the treatment of neurodegenerative diseases such as multiple sclerosis (MS). Previously, we reported the oral administration of resveratrol nanoparticles (RNs) elicited a neuroprotective effect in an experimental autoimmune encephalomyelitis (EAE) mouse model of MS, at significantly lower doses than unconjugated resveratrol (RSV) due to enhanced bioavailability. Furthermore, we demonstrated that the intranasal administration of a cell-derived secretome-based therapy at low concentrations leads to the selective neuroprotection of the optic nerve in EAE mice. The current study sought to assess the potential selective efficacy of lower concentrations of intranasal RNs for attenuating optic nerve damage in EAE mice.
EAE mice received either a daily intranasal vehicle, RNs or unconjugated resveratrol (RSV) for a period of thirty days beginning on the day of EAE induction. Mice were assessed daily for limb paralysis and weekly for visual function using the optokinetic response (OKR) by observers masked to treatment regimes. After sacrifice at day 30, spinal cords and optic nerves were stained to assess inflammation and demyelination, and retinas were immunostained to quantify retinal ganglion cell (RGC) survival.
Intranasal RNs significantly increased RGC survival at half the dose previously shown to be required when given orally, reducing the risk of systemic side effects associated with prolonged use. Both intranasal RSV and RN therapies enhanced RGC survival trends, however, only the effects of intranasal RNs were significant. RGC loss was prevented even in the presence of inflammatory and demyelinating changes induced by EAE in optic nerves.
The intranasal administration of RNs is able to reduce RGC loss independent of the inflammatory and demyelinating effects on the optic nerve and the spinal cord. The concentration of RNs needed to achieve neuroprotection is lower than previously demonstrated with oral administration, suggesting intranasal drug delivery combined with nanoparticle conjugation warrants further exploration as a potential neuroprotective strategy for the treatment of optic neuritis, alone as well as in combination with glucocorticoids
Lepton Flavor Violation and the Origin of the Seesaw Mechanism
The right--handed neutrino mass matrix that is central to the understanding
of small neutrino masses via the seesaw mechanism can arise either (i) from
renormalizable operators or (ii) from nonrenormalizable or super-renormalizable
operators, depending on the symmetries and the Higgs content of the theory
beyond the Standard Model. In this paper, we study lepton flavor violating
(LFV) effects in the first class of seesaw models wherein the \nu_R Majorana
masses arise from renormalizable Yukawa couplings involving a B-L = 2 Higgs
field. We present detailed predictions for \tau -> \mu + \gamma and \mu -> e +
\gamma branching ratios in these models taking the current neutrino oscillation
data into account. Focusing on minimal supergravity models, we find that for a
large range of MSSM parameters suggested by the relic abundance of neutralino
dark matter and that is consistent with Higgs boson mass and other constraints,
these radiative decays are in the range accessible to planned experiments. We
compare these predictions with lepton flavor violation in the second class of
models arising entirely from the Dirac Yukawa couplings. We study the
dependence of the ratio r \equiv B(\mu -> e+\gamma)/B(\tau ->\mu +\gamma) on
the MSSM parameters and show that measurement of r can provide crucial insight
into the origin of the seesaw mechanism.Comment: 20 pages, Revtex, 7 figure
Gravitational wave amplification of seed magnetic fields
We discuss how gravitational waves could amplify seed magnetic fields to
strengths capable of supporting the galactic dynamo. We consider the
interaction of a weak magnetic field with gravity wave distortions in almost
FRW cosmologies and find that the magnitude of the original field is amplified
proportionally to the wave induced shear anisotropy and, crucially,
proportionally to the square of the field's initial scale. The latter makes our
mechanism particularly efficient when operating on superhorizon sized magnetic
fields, like those produced during inflation. In that case, the achieved
amplification can easily boost magnetic strengths, which may still lie
relatively close to the galactic dynamo lower limits, well within the currently
accepted range.Comment: Revised version, to appear in Phys. Lett.
Planck Scale Symmetry Breaking and Majoron Physics
Majoron models provide neutrino masses via the spontaneous breaking of a
global symmetry. However, it may be argued that all global symmetries
will be explicitly violated by gravitational effects. We show that it is
possible to preserve most of the usual features of majoron models by invoking
to be a gauge symmetry and adding a second singlet scalar field.
The majoron gets a small model dependent mass. The couplings of majorons to
neutrinos may be of ordinary strength or may be made arbitrarily weak. We
discuss the cosmological and astrophysical consequences of majoron models in
the context of a model dependent majoron mass and neutrino coupling. For an
appropriate choice of parameters majorons can play the role of dark matter.Comment: 30 pages, UM-TH-92-3
Phenomenological Consequences of Singlet Neutrinos
In this paper, we study the phenomenology of right-handed neutrino
isosinglets. We consider the general situation where the neutrino masses are
not necessarily given by , where and are the Dirac and
Majorana mass terms respectively. The consequent mixing between the light and
heavy neutrinos is then not suppressed, and we treat it as an independent
parameter in the analysis. It turns out that conversion is an important
experiment in placing limits on the heavy mass scale () and the mixing.
Mixings among light neutrinos are constrained by neutrinoless double beta
decay, as well as by solar and atmospheric neutrino experiments. Detailed
one-loop calculations for lepton number violating vertices are provided.Comment: Revtex file,TRI-PP-94-1,VPI-IHEP-94-1, 23 pages, a compressed for 8
figures is appende
Planck scale effects in neutrino physics
We study the phenomenology and cosmology of the Majoron (flavon) models of
three active and one inert neutrino paying special attention to the possible
(almost) conserved generalization of the Zeldovich-Konopinski-Mahmoud lepton
charge. Using Planck scale physics effects which provide the breaking of the
lepton charge, we show how in this picture one can incorporate the solutions to
some of the central issues in neutrino physics such as the solar and
atmospheric neutrino puzzles, dark matter and a 17 keV neutrino. These
gravitational effects induce tiny Majorana mass terms for neutrinos and
considerable masses for flavons. The cosmological demand for the sufficiently
fast decay of flavons implies a lower limit on the electron neutrino mass in
the range of 0.1-1 eV.Comment: 24 pages, 1 figure (not included but available upon request), LaTex,
IC/92/196, SISSA-140/92/EP, LMU-09/9
Solar Neutrinos with Three Flavor Mixings
The recent 71Ga solar neutrino observation is combined with the 37Cl and
Kamiokande-II observations in an analysis for neutrino masses and mixings. The
allowed parameter region is found for matter enhanced mixings among all three
neutrino flavors. Distortions of the solar neutrino spectrum unique to three
flavors are possible and may be observed in continuing and next generation
experiments.Comment: August 1992 (Revised) PURD-TH-92-
Solar Neutrinos: What We Have Learned
The four operating solar neutrino experiments confirm the hypothesis that the
energy source for solar luminosity is hydrogen fusion. However, the measured
rate for each of the four solar neutrino experiments differs significantly (by
factors of 2.0 to 3.5) from the corresponding theoretical prediction that is
based upon the standard solar model and the simplest version of the standard
electroweak theory. If standard electroweak theory is correct, the energy
spectrum for \b8 neutrinos created in the solar interior must be the same (to
one part in ) as the known laboratory \b8 neutrino energy spectrum.
Direct comparison of the chlorine and the Kamiokande experiments, both
sensitive to \b8 neutrinos, suggests that the discrepancy between theory and
observations depends upon neutrino energy, in conflict with standard
expectations. Monte Carlo studies with 1000 implementations of the standard
solar model confirm that the chlorine and the Kamiokande experiments cannot be
reconciled unless new weak interaction physics changes the shape of the \b8
neutrino energy spectrum. The results of the two gallium solar neutrino
experiments strengthen the conclusion that new physics is required and help
determine a relatively small allowed region for the MSW neutrino parameters.Comment: LaTeX file, 19 pages. For hardcopy with figures contact
[email protected]. Institute for Advanced Study number AST 93/6
Possible Revelation of Seesaw Mass Pattern in Solar and Atmospheric Neutrino Data
Assuming the solar and atmospheric neutrino deficits to be due to neutrino
oscillations, it is shown that the 3X3 mass matrix spanning the e, mu, and tau
neutrinos may have already revealed a seesaw mass pattern. Also, this matrix is
the natural reduction of a simple 5X5 seesaw mass matrix with one large scale,
the 4X4 reduction of which predicts that a fourth neutrino would mix with the e
and mu neutrinos in such a way that oscillations between them may occur just
within the detection capability of the LSND (Liquid Scintillator Neutrino
Detector) experiment.Comment: 10 pages (4 figures not included
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