1,327 research outputs found
Acausality in Gowdy spacetimes
We present a parametrization of and Gowdy cosmological
models which allows us to study both types of topologies simultaneously. We
show that there exists a coordinate system in which the general solution of the
linear polarized special case (with both topologies) has exactly the same
functional dependence. This unified parametrization is used to investigate the
existence of Cauchy horizons at the cosmological singularities, leading to a
violation of the strong cosmic censorship conjecture. Our results indicate that
the only acausal spacetimes are described by the Kantowski-Sachs and the
Kerr-Gowdy metrics.Comment: Typos corrected, 10 pages. Dedicated to Michael P. Ryan on the
occasion of his 60-th birthda
The resummation of inter-jet energy flow for gaps-between-jets processes at HERA
We calculate resummed perturbative predictions for gaps-between-jets
processes and compare to HERA data. Our calculation of this non-global
observable needs to include the effects of primary gluon emission (global
logarithms) and secondary gluon emission (non-global logarithms) to be correct
at the leading logarithm (LL) level. We include primary emission by calculating
anomalous dimension matrices for the geometry of the specific event definitions
and estimate the effect of non-global logarithms in the large limit. The
resulting predictions for energy flow observables are consistent with
experimental data.Comment: 31 pages, 4 figures, 2 table
Tachyonization of the \LaCDM cosmological model
In this work a tachyonization of the CDM model for a spatially flat
Friedmann-Robertson-Walker space-time is proposed. A tachyon field and a
cosmological constant are considered as the sources of the gravitational field.
Starting from a stability analysis and from the exact solutions for a standard
tachyon field driven by a given potential, the search for a large set of
cosmological models which contain the CDM model is investigated. By
the use of internal transformations two new kinds of tachyon fields are derived
from the standard tachyon field, namely, a complementary and a phantom tachyon
fields. Numerical solutions for the three kinds of tachyon fields are
determined and it is shown that the standard and complementary tachyon fields
reproduces the CDM model as a limiting case. The standard tachyon
field can also describe a transition from an accelerated to a decelerated
regime, behaving as an inflaton field at early times and as a matter field at
late times. The complementary tachyon field always behaves as a matter field.
The phantom tachyon field is characterized by a rapid expansion where its
energy density increases with time.Comment: Version accepted for publication in GR
Osteogenic tumour in Australopithecus sediba: Earliest hominin evidence for neoplastic disease
We describe the earliest evidence for neoplastic disease in the hominin lineage. This is reported
from the type specimen of the extinct hominin Australopithecus sediba from Malapa, South Africa,
dated to 1.98 million years ago. The affected individual was male and developmentally equivalent
to a human child of 12 to 13 years of age. A penetrating lytic lesion affected the sixth thoracic
vertebra. The lesion was macroscopically evaluated and internally imaged through phase-contrast
X-ray synchrotron microtomography. A comprehensive differential diagnosis was undertaken
based on gross- and micro-morphology of the lesion, leading to a probable diagnosis of osteoid
osteoma. These neoplasms are solitary, benign, osteoid and bone-forming tumours, formed from
well-vascularised connective tissue within which there is active production of osteoid and woven
bone. Tumours of any kind are rare in archaeological populations, and are all but unknown in
the hominin record, highlighting the importance of this discovery. The presence of this disease
at Malapa predates the earliest evidence of malignant neoplasia in the hominin fossil record by
perhaps 200 000 years.NCS201
Electromagnetic proton form factors in large QCD
The electromagnetic form factors of the proton are obtained using a
particular realization of QCD in the large limit (),
which sums up the infinite number of zero-width resonances to yield an Euler's
Beta function (Dual-). The form factors and
, as well as agree very well with reanalyzed space-like
data in the whole range of momentum transfer. In addition, the predicted ratio
is in good agreement with recent polarization transfer
measurements at Jefferson Lab.Comment: 10 page
Earliest hominin cancer: 1.7-million-year- old osteosarcoma from Swartkrans Cave, South Africa
The reported incidence of neoplasia in the extinct human lineage is rare, with only a few confirmed
cases of Middle or Later Pleistocene dates reported. It has generally been assumed that premodern
incidence of neoplastic disease of any kind is rare and limited to benign conditions,
but new fossil evidence suggests otherwise. We here present the earliest identifiable case of
malignant neoplastic disease from an early human ancestor dated to 1.8â1.6 million years old.
The diagnosis has been made possible only by advances in 3D imaging methods as diagnostic
aids. We present a case report based on re-analysis of a hominin metatarsal specimen (SK 7923)
from the cave site of Swartkrans in the Cradle of Humankind, South Africa. The expression
of malignant osteosarcoma in the Swartkrans specimen indicates that whilst the upsurge in
malignancy incidence is correlated with modern lifestyles, there is no reason to suspect that
primary bone tumours would have been any less frequent in ancient specimens. Such tumours
are not related to lifestyle and often occur in younger individuals. As such, malignancy has a
considerable antiquity in the fossil record, as evidenced by this specimen.NCS201
Constraints on the pMSSM from LAT Observations of Dwarf Spheroidal Galaxies
We examine the ability for the Large Area Telescope (LAT) to constrain
Minimal Supersymmetric Standard Model (MSSM) dark matter through a combined
analysis of Milky Way dwarf spheroidal galaxies. We examine the Lightest
Supersymmetric Particles (LSPs) for a set of ~71k experimentally valid
supersymmetric models derived from the phenomenological-MSSM (pMSSM). We find
that none of these models can be excluded at 95% confidence by the current
analysis; nevertheless, many lie within the predicted reach of future LAT
analyses. With two years of data, we find that the LAT is currently most
sensitive to light LSPs (m_LSP < 50 GeV) annihilating into tau-pairs and
heavier LSPs annihilating into b-bbar. Additionally, we find that future LAT
analyses will be able to probe some LSPs that form a sub-dominant component of
dark matter. We directly compare the LAT results to direct detection
experiments and show the complementarity of these search methods.Comment: 24 pages, 9 figures, submitted to JCA
Observation of prompt single muons and of missing energy associated with pairs produced in hadronic interactions
In a study of interactions of 400 GeV protons in a totally absorbing iron calorimeter the authors report two observations indicating the hadronic production of heavy short-lived weakly decaying particles. First they have observed a prompt muon signal in the region .8<p/sub t /<2.5 GeV/c. The rate is comparable in magnitude to the prompt 2 mu rate in the same kinematic region. In addition to detecting mu /sup +/ mu /sup -/ events arising from electromagnetic sources (e.g. rho to mu /sup +/ mu /sup -/, psi to mu /sup +/ mu /sup -/ etc.) they have observed mu /sup +/ mu /sup -/ pairs associated with a significant amount of missing energy indicative of final state neutrinos. Interpreting these data as production of DD pairs followed by single or double muonic decays leads to a model dependent estimate of total production cross-section of order 15 mu b. (14 refs)
United classification of cosmic gamma-ray bursts and their counterparts
United classification of gamma-ray bursts and their counterparts is
established on the basis of measured characteristics: photon energy E and
emission duration T. The founded interrelation between the mentioned
characteristics of events consists in that, as the energy increases, the
duration decreases (and vice versa). The given interrelation reflects the
nature of the phenomenon and forms the E-T diagram, which represents a natural
classification of all observed events in the energy range from 10E9 to 10E-6 eV
and in the corresponding interval of durations from about 10E-2 up to 10E8 s.
The proposed classification results in the consequences, which are principal
for the theory and practical study of the phenomenon.Comment: Keywords Gamma rays: burst
Inelastic production in polarized photon-hadron collisions
Presented here is a calculation of inelastic production in polarized
photon-hadron collisions under the framework of NRQCD factorization formalism.
We consider the photoproduction of \jpsi in the energy range relevant to
HERA. The Weizs\"acker-Williams approximation is adopted in the evaluation of
the cross sections for collisions. We found that this process can give
another independent test for the color-octet mechanism, and the different
features for the two color-octet processes may provide further informations on
the mechanism for inelastic \jpsi photoproduction. And the discrepancy on the
production asymmetry between various sets of polarized gluon distribution
functions is also found to be distinctive.Comment: 14pages, 6 PS figure
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