245 research outputs found
Axion-like particles as ultra high energy cosmic rays?
If Ultra High Energy Cosmic Rays (UHECRs) with E>4 10^{19} eV originate from
BL Lacertae at cosmological distances as suggested by recent studies, the
absence of the GZK cutoff can not be reconciled with Standard-Model particle
properties. Axions would escape the GZK cutoff, but even the coherent
conversion and back-conversion between photons and axions in large-scale
magnetic fields is not enough to produce the required flux. However, one may
construct models of other novel (pseudo)scalar neutral particles with
properties that would allow for sufficient rates of particle production in the
source and shower production in the atmosphere to explain the observations. As
an explicit example for such particles we consider SUSY models with light
sgoldstinos.Comment: 5 pages, 2 postscript figures, ref. adde
B-1a cells acquire their unique characteristics by bypassing the pre-BCR selection stage
B-1a cells are long-lived, self-renewing innate-like B cells that predominantly inhabit the peritoneal and pleural cavities. In contrast to conventional B-2 cells, B-1a cells have a receptor repertoire that is biased towards bacterial and self-antigens, promoting a rapid response to infection and clearing of apoptotic cells. Although B-1a cells are known to primarily originate from fetal tissues, the mechanisms by which they arise has been a topic of debate for many years. Here we show that in the fetal liver versus bone marrow environment, reduced IL-7R/STAT5 levels promote immunoglobulin kappa gene recombination at the early pro-B cell stage. As a result, differentiating B cells can directly generate a mature B cell receptor (BCR) and bypass the requirement for a pre-BCR and pairing with surrogate light chain. This 'alternate pathway' of development enables the production of B cells with self-reactive, skewed specificity receptors that are peculiar to the B-1a compartment. Together our findings connect seemingly opposing lineage and selection models of B-1a cell development and explain how these cells acquire their unique properties
Effective Lagrangians for Orientifold Theories
We construct effective Lagrangians of the Veneziano-Yankielowicz (VY) type
for two non-supersymmetric theories which are orientifold daughters of
supersymmetric gluodynamics (containing one Dirac fermion in the two-index
antisymmetric or symmetric representation of the gauge group). Since the parent
and daughter theories are planar equivalent, at N\to\infty the effective
Lagrangians in the orientifold theories basically coincide with the bosonic
part of the VY Lagrangian.
We depart from the supersymmetric limit in two ways. First, we consider
finite (albeit large) values of N. Then 1/N effects break supersymmetry. We
suggest seemingly the simplest modification of the VY Lagrangian which
incorporates these 1/N effects, leading to a non-vanishing vacuum energy
density. We analyze the spectrum of the finite-N non-supersymmetric daughters.
For N=3 the two-index antisymmetric representation (one flavor) is equivalent
to one-flavor QCD. We show that in this case the scalar quark-antiquark state
is heavier than the corresponding pseudoscalar state, `` eta' ''. Second, we
add a small fermion mass term. The fermion mass term breaks supersymmetry
explicitly. The vacuum degeneracy is lifted. The parity doublets split. We
evaluate the splitting. Finally, we include the theta-angle and study its
implications.Comment: LaTeX, 21 page
Penguins leaving the pole: bound-state effects in B decaying to K* + photon
Applying perturbative QCD methods recently seen to give a good description of
the two body hadronic decays of the B meson, we address the question of
bound-state effects on the decay B into K* + gamma. Consistent with most
analyses, we demonstrate that gluonic penguins, with photonic bremsstrahlung
off a quark, change the decay rate by only a few percent. However, explicit
off-shell b-quark effects normally discarded are found to be large in
amplitude, although in the standard model accidents of phase minimize the
effect on the rate. Using an asymptotic distribution amplitude for the K* and
just the standard model, we can obtain a branching ratio of a few times
10^{-5}, consistent with the observed rate.Comment: 12 pages. U. of MD PP \#94-129; DOE/ER/40762-033; WM-94-104. LaTeX,
One figure, available by fax or pos
The clustering of ultra-high energy cosmic rays and their sources
The sky distribution of cosmic rays with energies above the 'GZK cutoff'
holds important clues to their origin. The AGASA data, although consistent with
isotropy, shows evidence for small-angle clustering, and it has been argued
that such clusters are aligned with BL Lacertae objects, implicating these as
sources. It has also been suggested that clusters can arise if the cosmic rays
come from the decays of very massive relic particles in the Galactic halo, due
to the expected clumping of cold dark matter. We examine these claims and show
that both are in fact not justified.Comment: 13 pages, 8 figures, version in press at Phys. Rev.
Ultra-High Energy Cosmic Rays from Neutrino Emitting Acceleration Sources?
We demonstrate by numerical flux calculations that neutrino beams producing
the observed highest energy cosmic rays by weak interactions with the relic
neutrino background require a non-uniform distribution of sources. Such sources
have to accelerate protons at least up to 10^{23} eV, have to be opaque to
their primary protons, and should emit the secondary photons unavoidably
produced together with the neutrinos only in the sub-MeV region to avoid
conflict with the diffuse gamma-ray background measured by the EGRET
experiment. Even if such a source class exists, the resulting large
uncertainties in the parameters involved in this scenario does currently not
allow to extract any meaningful information on absolute neutrino masses.Comment: 6 pages, 4 figures, RevTeX styl
Hadronic EDMs, the Weinberg Operator, and Light Gluinos
We re-examine questions concerning the contribution of the three-gluon
Weinberg operator to the electric dipole moment of the neutron, and provide
several QCD sum rule-based arguments that the result is smaller than - but
nevertheless consistent with - estimates which invoke naive dimensional
analysis. We also point out a regime of the MSSM parameter space with light
gluinos for which this operator provides the dominant contribution to the
neutron electric dipole moment due to enhancement via the dimension five color
electric dipole moment of the gluino.Comment: 6 pages, RevTeX, 3 figures; v2: references added; v3: typos
corrected, to appear in Phys. Rev.
The collective burden of childhood dementia: a scoping review
OnlinePublChildhood dementia is a devastating and under-recognised group of disorders with a high level of unmet need. Typically monogenic in origin, this collective of individual neurodegenerative conditions are defined by a progressive impairment of neurocognitive function, presenting in childhood and adolescence. This scoping review aims to clarify definitions and conceptual boundaries of childhood dementia and quantify the collective disease burden. A literature review identified conditions that met the case definition. An expert clinical working group reviewed and ratified inclusion. Epidemiological data were extracted from published literature and collective burden modelled. One hundred and seventy genetic childhood dementia disorders were identified. Of these, 25 were analysed separately as treatable conditions. Collectively, currently untreatable childhood dementia was estimated to have an incidence of 34.5 per 100,000 (1 in 2,900 births), median life expectancy of 9 years and prevalence of 5.3 per 100,000 persons. The estimated number of premature deaths per year is similar to childhood cancer (0-14 years) and approximately 70% of those deaths will be prior to adulthood. An additional 49.8 per 100,000 births are attributable to treatable conditions that would cause childhood dementia if not diagnosed early and stringently treated. A relational database of the childhood dementia disorders has been created and will be continually updated as new disorders are identified (https://knowledgebase.childhooddementia.org/). We present the first comprehensive overview of monogenic childhood dementia conditions and their collective epidemiology. Unifying these conditions, with consistent language and definitions, reinforces motivation to advance therapeutic development and health service supports for this significantly disadvantaged group of children and their families.Kristina L. Elvidge, John Christodoulou, Michelle A. Farrar, Dominic Tilden, Megan Maack, Madeline Valeri, Magda Ellis, Nicholas J. C. Smith, and the Childhood Dementia Working Grou
Charged Higgs boson and stau phenomenology in the simplest R-parity breaking model
We consider the charged scalar boson phenomenology in the simplest effective low-energy R-parity breaking model characterized by a bilinear violation of R-parity in the superpotential. This induces a mixing between staus and the charged Higgs boson. We show that the charged Higgs boson mass can be lower than expected in the MSSM, even before including radiative corrections. We also study the charged scalar boson decay branching ratios and show that the R-parity violating decay rates can be comparable or even bigger than the R-parity conserving ones. Moreover, if the stau is the LSP it will have only decays into standard model fermions. These features could have important implications for charged supersymmetric scalar boson searches at future accelerators
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