2,557 research outputs found
Seesaw Right Handed Neutrino as the Sterile Neutrino for LSND
We show that a double seesaw framework for neutrino masses with
exchange symmetry can lead to one of the righthanded seesaw partners of the
light neutrinos being massless. This can play the role of a light sterile
neutrino, giving a model that explains the LSND results. We get a very
economical scheme, which makes it possible to predict the full
neutrino mass matrix if CP is conserved. Once CP violation is included, effect
of the LSND mass range sterile neutrino is to eliminate the lower bound on
neutrinoless double beta decay rate which exists for the three neutrino case
with inverted mass hierarchy. The same strategy can also be used to generate a
natural model for LSND, which is also equally predictive for the CP
conserving case in the limit of exact symmetry.Comment: 13 pages and one figure; model extended to 3+2 cas
Supersymmetry Breaking by Type II Seesaw Assisted Anomaly Mediation
Anomaly mediated supersymmetry breaking (AMSB), when implemented in MSSM is
known to suffer from the problem of negative slepton mass squared leading to
breakdown of electric charge conservation. We show however that when MSSM is
extended to explain small neutrino masses by including a pair of superheavy
Higgs triplet superfields (the type II seesaw mechanism), the slepton masses
can be deflected from the pure AMSB trajectory and become positive. In a simple
model we present in this paper, the seesaw scale is about . Gauge coupling unification can be maintained by embedding the triplet to
SU(5) {\bf 15}-multiplet. In this scenario, bino is the LSP and its mass is
nearly degenerate with NLSP slepton when the triplet mass is right around the
seesaw scale.Comment: 18 pages, 4 figures, added references, added footnote
Innovative in silico approaches to address avian flu using grid technology
The recent years have seen the emergence of diseases which have spread very
quickly all around the world either through human travels like SARS or animal
migration like avian flu. Among the biggest challenges raised by infectious
emerging diseases, one is related to the constant mutation of the viruses which
turns them into continuously moving targets for drug and vaccine discovery.
Another challenge is related to the early detection and surveillance of the
diseases as new cases can appear just anywhere due to the globalization of
exchanges and the circulation of people and animals around the earth, as
recently demonstrated by the avian flu epidemics. For 3 years now, a
collaboration of teams in Europe and Asia has been exploring some innovative in
silico approaches to better tackle avian flu taking advantage of the very large
computing resources available on international grid infrastructures. Grids were
used to study the impact of mutations on the effectiveness of existing drugs
against H5N1 and to find potentially new leads active on mutated strains. Grids
allow also the integration of distributed data in a completely secured way. The
paper presents how we are currently exploring how to integrate the existing
data sources towards a global surveillance network for molecular epidemiology.Comment: 7 pages, submitted to Infectious Disorders - Drug Target
Nature of magnetic coupling between Mn ions in as-grown GaMnAs studied by x-ray magnetic circular dichroism
The magnetic properties of as-grown GaMnAs have been
investigated by the systematic measurements of temperature and magnetic field
dependent soft x-ray magnetic circular dichroism (XMCD). The {\it intrinsic}
XMCD intensity at high temperatures obeys the Curie-Weiss law, but residual
spin magnetic moment appears already around 100 K, significantly above Curie
temperature (), suggesting that short-range ferromagnetic correlations are
developed above . The present results also suggest that antiferromagnetic
interaction between the substitutional and interstitial Mn (Mn) ions
exists and that the amount of the Mn affects .Comment: 4 pages, 4 figure
An SO(10) GUT Model with Flavor Symmetry
We present a supersymmetric grand unification model based on SO(10) group
with flavor symmetry. In this model, the fermion masses are from Yukawa
couplings involving and Higgs multiplets and the
flavor structures of mass matrices of both quarks and leptons are determined by
spontaneously broken . This model fits all of the masses and mixing angles
of the quarks and leptons. For the most general CP-violation scenario, this
model gives a wide range of values from zero to the current
bound with the most probable values . With certain assumptions where
leptonic phases have same CP-violation source as CKM phase, one gets a narrower
range for with the most probable values
. This model gives leptonic Dirac CP phase the most probable values
2-4 radians in the general CP-violation case.Comment: 14 pages,2 figures. Version published in Physical Review
Tannaka-Krein duality for Hopf algebroids
We develop the Tannaka-Krein duality for monoidal functors with target in the
categories of bimodules over a ring. The \coend of such a functor turns out
to be a Hopf algebroid over this ring. Using the result of a previous paper we
characterize a small abelian, locally finite rigid monoidal category as the
category of rigid comodules over a transitive Hopf algebroid.Comment: 25 pages, final version, to appear in Israel Journal of Mathematic
Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap
Using two experimental techniques, we studied single crystals of the 122-FeAs
family with almost the same critical temperature, Tc. We investigated the
temperature dependence of the lower critical field of a single crystal under
static magnetic fields parallel to the axis. The temperature dependence of the
London penetration depth can be described equally well either by a single
anisotropic -wave-like gap or by a two-gap model, while a d-wave approach
cannot be used to fit the London penetration depth data. Intrinsic multiple
Andreev reflection effect spectroscopy was used to detect bulk gap values in
single crystals of the intimate compound, with the same Tc. We estimated the
range of the large gap value 6-8 meV (depending on small variation of and its a
space anisotropy of about 30%, and the small gap 1.7 meV. This clearly
indicates that the gap structure of our investigated systems more likely
corresponds to a nodeless s-wave two gaps.Comment: 9 pages, 6 figure
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