20,346 research outputs found
The bispectrum of redshifted 21-cm fluctuations from the dark ages
Brightness-temperature fluctuations in the redshifted 21-cm background from
the cosmic dark ages are generated by irregularities in the gas-density
distribution and can then be used to determine the statistical properties of
density fluctuations in the early Universe. We first derive the most general
expansion of brightness-temperature fluctuations up to second order in terms of
all the possible sources of spatial fluctuations. We then focus on the
three-point statistics and compute the angular bispectrum of
brightness-temperature fluctuations generated prior to the epoch of hydrogen
reionization. For simplicity, we neglect redshift-space distortions. We find
that low-frequency radio experiments with arcmin angular resolution can easily
detect non-Gaussianity produced by non-linear gravity with high signal-to-noise
ratio. The bispectrum thus provides a unique test of the gravitational
instability scenario for structure formation, and can be used to measure the
cosmological parameters. Detecting the signature of primordial non-Gaussianity
produced during or right after an inflationary period is more challenging but
still possible. An ideal experiment limited by cosmic variance only and with an
angular resolution of a few arcsec has the potential to detect primordial
non-Gaussianity with a non-linearity parameter of f_NL ~ 1. Additional sources
of error as weak lensing and an imperfect foreground subtraction could severely
hamper the detection of primordial non-Gaussianity which will benefit from the
use of optimal estimators combined with tomographic techniques.Comment: 15 pages, 4 figures, revised version accepted for publication in ApJ
(contains an improved discussion of gas temperature fluctuations
The Effects of Dark Matter Decay and Annihilation on the High-Redshift 21 cm Background
The radiation background produced by the 21 cm spin-flip transition of
neutral hydrogen at high redshifts can be a pristine probe of fundamental
physics and cosmology. At z~30-300, the intergalactic medium (IGM) is visible
in 21 cm absorption against the cosmic microwave background (CMB), with a
strength that depends on the thermal (and ionization) history of the IGM. Here
we examine the constraints this background can place on dark matter decay and
annihilation, which could heat and ionize the IGM through the production of
high-energy particles. Using a simple model for dark matter decay, we show
that, if the decay energy is immediately injected into the IGM, the 21 cm
background can detect energy injection rates >10^{-24} eV cm^{-3} sec^{-1}. If
all the dark matter is subject to decay, this allows us to constrain dark
matter lifetimes <10^{27} sec. Such energy injection rates are much smaller
than those typically probed by the CMB power spectra. The expected brightness
temperature fluctuations at z~50 are a fraction of a mK and can vary from the
standard calculation by up to an order of magnitude, although the difference
can be significantly smaller if some of the decay products free stream to lower
redshifts. For self-annihilating dark matter, the fluctuation amplitude can
differ by a factor <2 from the standard calculation at z~50. Note also that, in
contrast to the CMB, the 21 cm probe is sensitive to both the ionization
fraction and the IGM temperature, in principle allowing better constraints on
the decay process and heating history. We also show that strong IGM heating and
ionization can lead to an enhanced H_2 abundance, which may affect the earliest
generations of stars and galaxies.Comment: submitted to Phys Rev D, 14 pages, 8 figure
Determination of polarized parton distribution functions with recent data on polarization asymmetries
Global analysis has been performed within the next-to-leading order in
Quantum Chromodynamics (QCD) to determine polarized parton distributions with
new experimental data in spin asymmetries. The new data set includes JLab,
HERMES, and COMPASS measurements on spin asymmetry A_1 for the neutron and
deuteron in lepton scattering. Our new analysis also utilizes the double-spin
asymmetry for pi^0 production in polarized pp collisions, A_{LL}^{pi^0},
measured by the PHENIX collaboration. Because of these new data, uncertainties
of the polarized PDFs are reduced. In particular, the JLab, HERMES, and COMPASS
measurements are valuable for determining Delta d_v(x) at large x and Delta
qbar(x) at x~0.1. The PHENIX pi^0 data significantly reduce the uncertainty of
Delta g(x). Furthermore, we discuss a possible constraint on Delta g(x) at
large x by using the HERMES data on g_1^d in comparison with the COMPASS ones
at x~0.05.Comment: 11 pages, REVTeX, 13 eps files, Phys. Rev. D in pres
Calculation of The Lifetimes of Thin Stripper Targets Under Bombardment of Intense Pulsed Ions
The problems of stripper target behavior in the nonstationary intense
particle beams are considered. The historical sketch of studying of radiation
damage failure of carbon targets under ion bombardment is presented. The simple
model of evaporation of a target by an intensive pulsing beam is supposed.
Stripper foils lifetimes in the nonstationary intense particle can be described
by two failure mechanisms: radiation damage accumulation and evaporation of
target. At the maximal temperatures less than 2500K the radiation damage are
dominated; at temperatures above 2500K the mechanism of evaporation of a foil
prevails. The proposed approach has been applied to the discription of
behaviour of stripper foils in the BNL linac and SNS conditions.Comment: 12 pages, 5 figure
Scalability tests of R-GMA-based grid job monitoring system for CMS Monte Carlo data production
Copyright @ 2004 IEEEHigh-energy physics experiments, such as the compact muon solenoid (CMS) at the large hadron collider (LHC), have large-scale data processing computing requirements. The grid has been chosen as the solution. One important challenge when using the grid for large-scale data processing is the ability to monitor the large numbers of jobs that are being executed simultaneously at multiple remote sites. The relational grid monitoring architecture (R-GMA) is a monitoring and information management service for distributed resources based on the GMA of the Global Grid Forum. We report on the first measurements of R-GMA as part of a monitoring architecture to be used for batch submission of multiple Monte Carlo simulation jobs running on a CMS-specific LHC computing grid test bed. Monitoring information was transferred in real time from remote execution nodes back to the submitting host and stored in a database. In scalability tests, the job submission rates supported by successive releases of R-GMA improved significantly, approaching that expected in full-scale production
The Sources of b-Quarks at the Tevatron and their Correlations
The leading-log order QCD hard scattering Monte-Carlo models of HERWIG,
ISAJET, and PYTHIA are used to study the sources of b-quarks at the Tevatron.
The reactions responsible for producing b and bbar quarks are separated into
three categories; flavor creation, flavor excitation, and
parton-shower/fragmentation. Flavor creation corresponds to the production of a
b-bbar pair by gluon fusion or by annihilation of light quarks, while flavor
excitation corresponds to a b or bbar quark being knocked out of the
initial-state by a gluon or a light quark or antiquark. The third source occurs
when a b-bbar pair is produced within a parton shower or during the
fragmentation process of a gluon or a light quark or antiquark (includes gluon
splitting). The QCD Monte-Carlo models indicate that all three sources of
b-quarks are important at the Tevatron and when combined they qualitatively
describe the inclusive cross-section data. Correlations between the b and bbar
quark are very different for the three sources and can be used to isolate the
individual contributions.Comment: RevTex4, 14 pages, 20 figures, submitted to Phys. Rev.
Equilibration in Quark Gluon Plasma
The hydrodynamic expansion rate of quark gluon plasma (QGP) is evaluated and
compared with the scattering rate of quarks and gluons within the system.
Partonic scattering rates evaluated within the ambit of perturbative Quantum
Choromodynamics (pQCD) are found to be smaller than the expansion rate
evaluated with ideal equation of state (EoS) for the QGP. This indicate that
during the space-time evolution the system remains out of equilibrium.
Enhancement of pQCD cross sections and a more realistic EoS keep the partons
closer to the equilibrium.Comment: To be published in the Quark Matter 2008 poster proceeding
Hormone replacement therapy use dramatically increases breast oestrogen receptor expression in obese postmenopausal women
BACKGROUND: It is known that use of hormone replacement therapy (HRT) by postmenopausal women increases the risk of breast cancer. METHOD: In this study, oestrogen receptor (ER)-α expression is examined using standard immunoperoxidase technique. RESULTS: Normal breast samples of 11 Australian postmenopausal women have been included in the ER-α study; the result showed a strong correlation (r(2) = 0.80) between ER-α expression in normal breast epithelial cells and body mass index (BMI) in normal women who currently use HRT. CONCLUSION: This finding confirms that the possibility of increased risk of breast cancer associated with increased ER-α expression in normal breast epithelial cells, in turn associated with high BMI and the use of HRT
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