4,810 research outputs found
Integrability of the Minimal Strain Equations for the Lapse and Shift in 3+1 Numerical Relativity
Brady, Creighton and Thorne have argued that, in numerical relativity
simulations of the inspiral of binary black holes, if one uses lapse and shift
functions satisfying the ``minimal strain equations'' (MSE), then the
coordinates might be kept co-rotating, the metric components would then evolve
on the very slow inspiral timescale, and the computational demands would thus
be far smaller than for more conventional slicing choices. In this paper, we
derive simple, testable criteria for the MSE to be strongly elliptic, thereby
guaranteeing the existence and uniqueness of the solution to the Dirichlet
boundary value problem. We show that these criteria are satisfied in a test-bed
metric for inspiraling binaries, and we argue that they should be satisfied
quite generally for inspiraling binaries. If the local existence and uniqueness
that we have proved holds globally, then, for appropriate boundary values, the
solution of the MSE exhibited by Brady et. al. (which tracks the inspiral and
keeps the metric evolving slowly) will be the unique solution and thus should
be reproduced by (sufficiently accurate and stable) numerical integrations.Comment: 6 pages; RevTeX; submitted to Phys. Rev. D15. Technical issue of the
uniqueness of the solution to the Dirichlet problem clarified. New subsection
on the nature of the boundary dat
Enhancement of prompt photons in ultrarelativistic proton-proton collisions from nonlinear gluon evolution at small-
In this paper we estimate the influence of nonlinear gluon evolution in the
production of prompt photons at the LHC pp collider. We assume the validity of
collinear factorization and consider the EHKQS parton distributions, which are
solutions of the GLR-MQ evolution equations and describe quite well the DESY
HERA data, as input in our calculations. We find that both single and
double photon production are enhanced for low- photons and central
rapidities, while this effect is absent for the high- photons. The
implications of this effect for the Quark-Gluon Plasma searches and for the QCD
background to Higgs are also discussed.Comment: 4 pages, 4 figures. Version to be published in Physical Review
No-horizon theorem for spacetimes with spacelike G1 isometry groups
We consider four-dimensional spacetimes which obey the
Einstein equations , and admit a global spacelike
isometry group. By means of dimensional reduction and local
analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on
which guarantees that cannot contain apparent
horizons. Given any (3+1) spacetime with spacelike translational isometry, the
no-horizon condition can be readily tested without the need for dimensional
reduction. This provides thus a useful and encompassing apparent horizon test
for -symmetric spacetimes. We argue that this adds further evidence
towards the validity of the hoop conjecture, and signals possible violations of
strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra
Nuclear shadowing from exclusive quarkonium photoproduction at the BNL RHIC and CERN LHC
The photonuclear production of vector mesons in ultraperipheral heavy ion
collisions is investigated within the collinear approach using different
parameterizations for the nuclear gluon distribution. The integrated cross
section and the rapidity distribution for the () process are computed for energies of RHIC and LHC. A comparison with
the recent PHENIX data on coherent production of mesons is also
presented. We demonstrate that the study of the exclusive quarkonium
photoproduction can be used to constrain the nuclear effects in the gluon
distribution.Comment: 8 pages, 4 figures, 2 tables. Version to be published in Physical
Review
Radion production in exclusive processes at CERN LHC
In the Randall-Sundrum (RS) scenario the compactification radius of the extra
dimension is stabilized by the radion, which is a scalar field lighter than the
graviton Kaluza-Klein states. It implies that the detection of the radion will
be the first signature of the stabilized RS model. In this paper we study the
exclusive production of the radion in electromagnetic and diffractive hadron -
hadron collisions at the LHC. Our results demonstrate that the diffractive
production of radion is dominant and should be feasible of study at CERN LHC.Comment: 6 pages, 3 figures, 1 tabl
On the exact Foldy-Wouthuysen transformation for a Dirac spinor in torsion and other CPT and Lorentz violating backgrounds
We discuss the possibility to perform and use the exact Foldy-Wouthuysen
transformation (EFWT) for the Dirac spinor coupled to different CPT and Lorentz
violating terms. The classification of such terms is performed, selecting those
of them which admit EFWT. For the particular example of an axial vector field,
which can be associated with the completely antisymmetric torsion, we construct
an explicit EFWT in the case when only a timelike component of this axial
vector is present. In the cases when EFWT is not possible, one can still use
the corresponding technique for deriving the perturbative Foldy-Wouthuysen
transformation, as is illustrated in a particular example in the Appendix
18F-FDG-PET/CT in diagnosis of Q fever endocarditis
info:eu-repo/semantics/publishedVersio
The ground state properties of the spin-1/2 transverse Ising chain with periodically varying bonds and fields
Using continued fractions we study the ground state properties of the
spin-1/2 Ising chain in a transverse field with periodically varying
interaction strengths and external fields. We consider in detail the chain
having the period of modulation of interactions equals 2 and compare the
results obtained with those corresponding to the spin-1/2 isotropic XY chain in
a transverse field. In contrast to the behaviour of the transverse XY chain,
the transverse Ising chain does not exhibit a step-like magnetization vs. field
dependence caused by the alternation of bonds, its susceptibility exhibits a
logarithmic singularity at the field determined by interaction strengths, and
it is stable with respect to spin-Peierls dimerization.Comment: 11 pages, latex, 4 figure
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