6,653 research outputs found
NLO-QCD Corrections to Dilepton Production in the Randall-Sundrum Model
The dilepton production process at hadron colliders in the Randall-Sundrum
(RS) model is studied at next-to-leading order in QCD. The NLO-QCD corrections
have been computed for the virtual graviton exchange process in the RS model,
in addition to the usual gamma, Z-mediated processes of standard Drell-Yan.
K-factors for the cross-sections at the LHC and Tevatron for differential in
the invariant mass, Q, and the rapidity, Y, of the lepton pair are presented.
We find the K-factors are large over substantial regions of the phase space.Comment: 24 pages, 12 figure
Generation of Curvature Perturbations with Extra Anisotropic Stress
We study the evolution of curvature perturbations and the cosmic microwave
background (CMB) power spectrum in the presence of an hypothesized extra
anisotropic stress which might arise, for example, from the dark radiation term
in brane-world cosmology. We evolve the scalar modes of such perturbations
before and after neutrino decoupling and analyze their effects on the CMB
spectrum. A novel result of this work is that the cancellation of the neutrino
and extra anisotropic stress could lead to a spectrum of residual curvature
perturbations which is similar to the observed CMB power spectrum. This implies
a possible additional consideration in the determination of cosmological
parameters from the CMB analysis.Comment: 13 pages, 2 figures; improved discussio
Data-Optimized Coronal Field Model: I. Proof of Concept
Deriving the strength and direction of the three-dimensional (3D) magnetic
field in the solar atmosphere is fundamental for understanding its dynamics.
Volume information on the magnetic field mostly relies on coupling 3D
reconstruction methods with photospheric and/or chromospheric surface vector
magnetic fields. Infrared coronal polarimetry could provide additional
information to better constrain magnetic field reconstructions. However,
combining such data with reconstruction methods is challenging, e.g., because
of the optical-thinness of the solar corona and the lack and limitations of
stereoscopic polarimetry. To address these issues, we introduce the
Data-Optimized Coronal Field Model (DOCFM) framework, a model-data fitting
approach that combines a parametrized 3D generative model, e.g., a magnetic
field extrapolation or a magnetohydrodynamic model, with forward modeling of
coronal data. We test it with a parametrized flux rope insertion method and
infrared coronal polarimetry where synthetic observations are created from a
known "ground truth" physical state. We show that this framework allows us to
accurately retrieve the ground truth 3D magnetic field of a set of force-free
field solutions from the flux rope insertion method. In observational studies,
the DOCFM will provide a means to force the solutions derived with different
reconstruction methods to satisfy additional, common, coronal constraints. The
DOCFM framework therefore opens new perspectives for the exploitation of
coronal polarimetry in magnetic field reconstructions and for developing new
techniques to more reliably infer the 3D magnetic fields that trigger solar
flares and coronal mass ejections.Comment: 14 pages, 6 figures; Accepted for publication in Ap
Revised Relativistic Hydrodynamical Model for Neutron-Star Binaries
We report on numerical results from a revised hydrodynamic simulation of
binary neutron-star orbits near merger. We find that the correction recently
identified by Flanagan significantly reduces but does not eliminate the
neutron-star compression effect. Although results of the revised simulations
show that the compression is reduced for a given total orbital angular
momentum, the inner most stable circular orbit moves to closer separation
distances. At these closer orbits significant compression and even collapse is
still possible prior to merger for a sufficiently soft EOS. The reduced
compression in the corrected simulation is consistent with other recent studies
of rigid irrotational binaries in quasiequilibrium in which the compression
effect is observed to be small. Another significant effect of this correction
is that the derived binary orbital frequencies are now in closer agreement with
post-Newtonian expectations.Comment: Submitted to Phys. Rev.
Direct Signals for Large Extra Dimensions in the Production of Fermion Pairs at Linear Colliders
We analyze the potentiality of the new generation of linear
colliders to search for large extra dimensions via the production of fermion
pairs in association with Kaluza-Klein gravitons (G), i.e. . This process leads to a final state exhibiting a significant amount
of missing energy in addition to acoplanar lepton or jet pairs. We study in
detail this reaction using full tree level contibutions due to the graviton
emission and the standard model backgrounds. After choosing the cuts to enhance
the signal, we show that a linear collider with a center-of-mass energy of 500
GeV will be able to probe quantum gravity scales from 0.96(0.86) up to 4.1(3.3)
TeV at 2(5) level, depending on the number of extra dimensions.Comment: 19 pages, 5 figures. Using RevTex, axodraw.sty. Discussion was
extended. No changes in the results. Accepted for publication by Phys. Rev.
Di-jet production at the LHC through unparticles
We report the phenomenological impact of unparticles in the production of
di-jet at the LHC. We compute the scalar, spin-1 and spin-2 unparticle
contributions to the dijet cross sections and present our results in different
kinematical distributions. We find that the scalar unparticle contribution is
dominant over that of the spin-1 and spin-2 unparticles for the same coupling
values.Comment: 17 pages, 10 eps figures, 4 tables. Spin-1 unparticles also included.
This version to appear in PR
Semi-analytical Solution of Dirac equation in Schwarzschild Geometry
Separation of the Dirac equation in the spacetime around a Kerr black hole
into radial and angular coordinates was done by Chandrasekhar in 1976. In the
present paper, we solve the radial equations in a Schwarzschild geometry
semi-analytically using Wentzel-Kramers-Brillouin approximation (in short WKB)
method. Among other things, we present analytical expression of the
instantaneous reflection and transmission coefficients and the radial wave
functions of the Dirac particles. Complete physical parameter space was divided
into two parts depending on the height of the potential well and energy of the
incoming waves. We show the general solution for these two regions. We also
solve the equations by a Quantum Mechanical approach, in which the potential is
approximated by a series of steps and found that these two solutions agree. We
compare solutions of different initial parameters and show how the properties
of the scattered wave depend on these parameters.Comment: RevTex, 11 Latex pages and 12 Figures ; Classical and Quantum Gravity
(in Press) (1999
On Constraining Electroweak-Baryogenesis with Inhomogeneous Primordial Nucleosynthesis
Primordial nucleosynthesis calculations are shown to be able to provide
constraints on electroweak baryogenesis which produce a highly inhomogeneous
distribution of the baryon-to-photon ratio. Such baryogenesis scenarios
overproduce 4He and/or 7Li and can be ruled out whenever a fraction
f<3*10e-6(100 GeV/T)^3 of nucleated bubbles of broken-symmetry phase
contributes > 10% of the baryon number within the horizon volume.Comment: 16 pages, 3 figures (figures available by email), UCRL-JC-11522
Salvage with a mini-allograft after primary engraftment failure following autologous transplant for multiple myeloma
This article does not have an abstract
Towards an evidence-based approach to fostering collaborative conversation in mainstream primary classrooms: Response to commentators
The ability to engage with ease in collaborative conversation is critical for child well-being and development. While key underpinning skills are biologically enabled, children require appropriate scaffolding and practice opportunities to develop proficient social conversational ability. Teaching conversation skills is a statutory requirement of the English primary (and many other) curricula. However, currently most upper primary mainstream teachers are not trained to teach conversation skills and do not teach them in the classroom or provide time for children to practice. We argue for first steps towards an evidence-based approach for a universal/Tier 1 programme, while fully acknowledging an ongoing need for Tier 2 and Tier 3 support as well as for further research into the strategies which are most effective in Tier 2/3 contexts. Further research is also needed to explore cultural variation in social conversation and to develop reliable, valid and brief teacher measures of child social conversational ability
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