348 research outputs found
Comparison of NNLO DIS scheme splitting functions with results from exact gluon kinematics at small x.
We consider the effect of exact gluon kinematics in the virtual photon-gluon impact factor at small
x. By comparing with fixed order DIS scheme splitting and coefficient functions, we show that the exact
kinematics results match the fixed order results well at each order, which suggests that they allow for an
accurate NLL analysis of proton structure functions. We also present, available for the first time, x-space
parameterisations of the NNLO DGLAP splitting functions in the DIS scheme, and also the longitudinal
coefficients for neutral current scattering
A Variable flavor number scheme for heavy quark production at small x.
We define a new variable flavour number scheme for use in deep inelastic scattering, motivated by
the need to consistently implement high energy resummations alongside a fixed order QCD expansion.
We define the DIS( ) scheme at fixed order, and show how to obtain the small x coefficient functions
and heavy flavour matrix elements to leading order in the high energy resummation. We then implement
these results in a global fit at LO which includes leading resummations with running coupling corrections.
Finally, we address the impact of the resummed results on predictions for the longitudinal structure
function. We find that they stabilise the behaviour of FL at small x. Overall, we find that resummations
significantly improve the fit to scattering data in the low x regime, although higher orders in the fixed
order expansion are needed to describe current structure function and related data over the complete x
range
The Virtual photon-gluon impact factor with massive quarks and exact gluon kinematics.
e calculate the impact factor coupling a virtual photon to a gluon via a massive quark-antiquark
pair at LL order, but with the imposition of the correct gluon kinematics. Exact analytical results are
presented in triple Mellin space with respect to scaled Bjorken x, gluon transverse momentum and heavy
quark mass. The application of these results to the calculation of approximate NLL coefficient functions
needed to relate structure functions to the BFKL gluon is presented. The NLL effects with running
coupling are seen to lead to a suppression of the small x divergence when compared with the fixed and
running coupling LL results, but less than in the massless case
Population-Level Benefits from Providing Effective HIV Prevention Means to Pregnant Women in High Prevalence Settings
Background:HIV prevalence among pregnant women in Southern Africa is extremely high. Epidemiological studies suggest that pregnancy increases the risk of HIV sexual acquisition and that HIV infections acquired during pregnancy carry higher risk of mother-to-child transmission (MTCT). We analyze the potential benefits from extending the availability of effective microbicide to pregnant women (in addition to non-pregnant women) in a wide-scale intervention.Methods and Findings:A transmission dynamic model was designed to assess the impact of microbicide use in high HIV prevalence settings and to estimate proportions of new HIV infections, infections acquired during pregnancy, and MTCT prevented over 10 years. Our analysis suggests that consistent use of microbicide with 70% efficacy by 60% of non-pregnant women may prevent approximately 40% and 15% of new infections in women and men respectively over 10 years, assuming no additional increase in HIV risk to either partner during pregnancy (RRHIV/preg = 1). It may also prevent 8-15% MTCT depending on the increase in MTCT risk when HIV is acquired during pregnancy compared to before pregnancy (RRMTCT/preg). Extending the microbicides use during pregnancy may improve the effectiveness of the intervention by 10% (RRHIV/preg = 1) to 25% (RRHIV/preg = 2) and reduce the number of HIV infections acquired during pregnancy by 40% to 70% in different scenarios. It may add between 6% (RRHIV/preg = 1, RRMTCT/preg = 1) and 25% (RRHIV/preg = 2, RRMTCT/preg = 4) to the reduction in the residual MTCT.Conclusion:Providing safe and effective microbicide to pregnant women in the context of wide-scale interventions would be desirable as it would increase the effectiveness of the intervention and significantly reduce the number of HIV infections acquired during pregnancy. The projected benefits from covering pregnant women by the HIV prevention programs is more substantial in communities in which the sexual risk during pregnancy is elevated. © 2013 Dimitrov et al
High energy emission from microquasars
The microquasar phenomenon is associated with the production of jets by X-ray
binaries and, as such, may be associated with the majority of such systems. In
this chapter we briefly outline the associations, definite, probable, possible,
and speculative, between such jets and X-ray, gamma-ray and particle emission.Comment: Contributing chapter to the book Cosmic Gamma-Ray Sources, K.S. Cheng
and G.E. Romero (eds.), to be published by Kluwer Academic Publishers,
Dordrecht, 2004. (19 pages
Non-homologous end-joining pathway associated with occurrence of myocardial infarction: gene set analysis of genome-wide association study data
<p>Purpose: DNA repair deficiencies have been postulated to play a role in the development and progression of cardiovascular disease (CVD). The hypothesis is that DNA damage accumulating with age may induce cell death, which promotes formation of unstable plaques. Defects in DNA repair mechanisms may therefore increase the risk of CVD events. We examined whether the joints effect of common genetic variants in 5 DNA repair pathways may influence the risk of CVD events.</p>
<p>Methods: The PLINK set-based test was used to examine the association to myocardial infarction (MI) of the DNA repair pathway in GWAS data of 866 subjects of the GENetic DEterminants of Restenosis (GENDER) study and 5,244 subjects of the PROspective Study of Pravastatin in the Elderly at Risk (PROSPER) study. We included the main DNA repair pathways (base excision repair, nucleotide excision repair, mismatch repair, homologous recombination and non-homologous end-joining (NHEJ)) in the analysis.</p>
<p>Results: The NHEJ pathway was associated with the occurrence of MI in both GENDER (P = 0.0083) and PROSPER (P = 0.014). This association was mainly driven by genetic variation in the MRE11A gene (PGENDER = 0.0001 and PPROSPER = 0.002). The homologous recombination pathway was associated with MI in GENDER only (P = 0.011), for the other pathways no associations were observed.</p>
<p>Conclusion: This is the first study analyzing the joint effect of common genetic variation in DNA repair pathways and the risk of CVD events, demonstrating an association between the NHEJ pathway and MI in 2 different cohorts.</p>
Gravitational Waves from Gravitational Collapse
Gravitational wave emission from the gravitational collapse of massive stars
has been studied for more than three decades. Current state of the art
numerical investigations of collapse include those that use progenitors with
realistic angular momentum profiles, properly treat microphysics issues,
account for general relativity, and examine non--axisymmetric effects in three
dimensions. Such simulations predict that gravitational waves from various
phenomena associated with gravitational collapse could be detectable with
advanced ground--based and future space--based interferometric observatories.Comment: 68 pages including 13 figures; revised version accepted for
publication in Living Reviews in Relativity (http://www.livingreviews.org
Gravitational effective action at second order in curvature and gravitational waves
We consider the full effective theory for quantum gravity at second order in curvature including non-local terms. We show that the theory contains two new degrees of freedom beyond the massless graviton: namely a massive spin-2 ghost and a massive scalar field. Furthermore, we show that it is impossible to fine-tune the parameters of the effective action to eliminate completely the classical spin-2 ghost because of the non-local terms in the effective action. Being a classical field, it is not clear anyway that this ghost is problematic. It simply implies a repulsive contribution to Newton’s potential. We then consider how to extract the parameters of the effective action and show that it is possible to measure, at least in principle, the parameters of the local terms independently of each other using a combination of observations of gravitational waves and measurements performed by pendulum type experiments searching for deviations of Newton’s potential
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
The high energy neutrino cross-section in the Standard Model and its uncertainty
Updated predictions are presented for high energy neutrino and antineutrino
charged and neutral current cross-sections within the conventional DGLAP
formalism of NLO QCD using modern PDF fits. PDF uncertainties from model
assumptions and parametrization bias are considered in addition to the
experimental uncertainties. Particular attention is paid to assumptions and
biases which could signal the need for extension of the conventional formalism
to include effects such as ln(1/x) resummation or non-linear effects of high
gluon density.Comment: 15 pages, 13 figures, 2 tables (REVTeX4); clarifying comments and
link to tabulated cross sections at
http://www-pnp.physics.ox.ac.uk/~cooper/neutrino/ added; to appear in JHE
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