3,131 research outputs found
The thermal model on the verge of the ultimate test: particle production in Pb-Pb collisions at the LHC
We investigate the production of hadrons in nuclear collisions within the
framework of the thermal (or statistical hadronization) model. We discuss both
the ligh-quark hadrons as well as charmonium and provide predictions for the
LHC energy. Even as its exact magnitude is dependent on the charm production
cross section, not yet measured in Pb-Pb collisions, we can confidently predict
that at the LHC the nuclear modification factor of charmonium as a function of
centrality is larger than that observed at RHIC and compare the experimental
results to these predictions.Comment: 4 pages, 3 figures; proceedings of QM201
The transition zone as a host for recycled volatiles: Evidence from nitrogen and carbon isotopes in ultra-deep diamonds from Monastery and Jagersfontein (South Africa)
Sublithospheric (ultra-deep) diamonds provide a unique window into the deepest parts of Earth's mantle, which otherwise remain inaccessible. Here, we report the first combined C- and N-isotopic data for diamonds from the Monastery and Jagersfontein kimberlites that sample the deep asthenosphere and transition zone beneath the Kaapvaal Craton, in the mid Cretaceous, to investigate the nature of mantle fluids at these depths and the constraints they provide on the deep volatile cycle.
Both diamond suites exhibit very light ÎŽ13C values (down to â 26â°) and heavy ÎŽ15N (up to + 10.3â°), with nitrogen abundances generally below 70 at. ppm but varying up to very high concentrations (2520 at. ppm) in rare cases. Combined, these signatures are consistent with derivation from subducted crustal materials. Both suites exhibit variable nitrogen aggregation states from 25 to 100% B defects. Internal growth structures, revealed in cathodoluminescence (CL) images, vary from faintly layered, through distinct cores to concentric growth patterns with intermittent evidence for dissolution and regular octahedral growth layers in places.
Modelling the internal co-variations in ÎŽ13C-ÎŽ15N-N revealed that diamonds grew from diverse C-H-O-N fluids involving both oxidised and reduced carbon species. The diversity of the modelled diamond-forming fluids highlights the complexity of the volatile sources and the likely heterogeneity of the deep asthenosphere and transition zone. We propose that the Monastery and Jagersfontein diamonds form in subducted slabs, where carbon is converted into either oxidised or reduced species during fluid-aided dissolution of subducted carbon before being re-precipitated as diamond. The common occurrence of recycled C and N isotopic signatures in super-deep diamonds world-wide indicates that a significant amount of carbon and nitrogen is recycled back to the deep asthenosphere and transition zone via subducting slabs, and that the transition zone may be dominated by recycled C and N
Has the Quark-Gluon Plasma been seen?
Data from the first three years of running at RHIC are reviewed and put into
context with data obtained previously at the AGS and SPS and with the physics
question of creation of a quark-gluon plasma in high energy heavy ion
collisions. Also some very recent and still preliminary data from run4 are
included.Comment: plenary paper, Lepton-Photon 2005, Uppsala, Swede
Gravitational strings. Do we see one?
I present a class of objects called gravitational strings (GS) for their
similarity to the conventional cosmic strings: even though the former are just
singularities in flat spacetime, both varieties are equally "realistic", they
may play equally important cosmological r\^ole and their lensing properties are
akin. I argue that the enigmatic object CSL-1 is an evidence in favor of the
existence of GS.Comment: The published version. Minor correction
Production of Strange Clusters and Strange Matter in Nucleus-Nucleus Collisions at the AGS
Production probabilities for strange clusters and strange matter in Au+Au
collisions at AGS energy are obtained in the thermal fireball model. The only
parameters of the model, the baryon chemical potential and temperature, were
determined from a description of the rather complete set of hadron yields from
Si+nucleus collisions at the AGS. For the production of light nuclear fragments
and strange clusters the results are similar to recent coalescence model
calculations. Strange matter production with baryon number larger than 10 is
predicted to be much smaller than any current experimental sensitivities.Comment: 9 Pages (no figures
Rotating magnetic solution in three dimensional Einstein gravity
We obtain the magnetic counterpart of the BTZ solution, i.e., the rotating
spacetime of a point source generating a magnetic field in three dimensional
Einstein gravity with a negative cosmological constant. The static
(non-rotating) magnetic solution was found by Clement, by Hirschmann and Welch
and by Cataldo and Salgado. This paper is an extension of their work in order
to include (i) angular momentum, (ii) the definition of conserved quantities
(this is possible since spacetime is asymptotically anti-de Sitter), (iii)
upper bounds for the conserved quantities themselves, and (iv) a new
interpretation for the magnetic field source. We show that both the static and
rotating magnetic solutions have negative mass and that there is an upper bound
for the intensity of the magnetic field source and for the value of the angular
momentum. The magnetic field source can be interpreted not as a vortex but as
being composed by a system of two symmetric and superposed electric charges,
one of the electric charges is at rest and the other is spinning. The rotating
magnetic solution reduces to the rotating uncharged BTZ solution when the
magnetic field source vanishes.Comment: Latex (uses JHEP3.cls), 12 pages. Published versio
The Physical Role of Gravitational and Gauge Degrees of Freedom in General Relativity - II: Dirac versus Bergmann observables and the Objectivity of Space-Time
(abridged)The achievements of the present work include: a) A clarification of
the multiple definition given by Bergmann of the concept of {\it (Bergmann)
observable. This clarification leads to the proposal of a {\it main conjecture}
asserting the existence of i) special Dirac's observables which are also
Bergmann's observables, ii) gauge variables that are coordinate independent
(namely they behave like the tetradic scalar fields of the Newman-Penrose
formalism). b) The analysis of the so-called {\it Hole} phenomenology in strict
connection with the Hamiltonian treatment of the initial value problem in
metric gravity for the class of Christoudoulou -Klainermann space-times, in
which the temporal evolution is ruled by the {\it weak} ADM energy. It is
crucial the re-interpretation of {\it active} diffeomorphisms as {\it passive
and metric-dependent} dynamical symmetries of Einstein's equations, a
re-interpretation which enables to disclose their (nearly unknown) connection
to gauge transformations on-shell; this is expounded in the first paper
(gr-qc/0403081). The use of the Bergmann-Komar {\it intrinsic
pseudo-coordinates} allows to construct a {\it physical atlas} of 4-coordinate
systems for the 4-dimensional {\it mathematical} manifold, in terms of the
highly non-local degrees of freedom of the gravitational field (its four
independent {\it Dirac observables}), and to realize the {\it physical
individuation} of the points of space-time as {\it point-events} as a
gauge-fixing problem, also associating a non-commutative structure to each
4-coordinate system.Comment: 41 pages, Revtex
Finite Temperature Gauge Theory on Anisotropic Lattices
The finite temperature transition of QCD can be seen as a change in the
structure of the hadrons and as a symmetry breaking transition -- a change in
the structure of the vacuum. These phenomena are observed differently and carry
complementary information. We aim at a correlated analysis involving hadronic
correlators and the vacuum structure including field and density correlations,
both non-trivial questions.Comment: 3 pages, Talk presented at LATTICE96(finite temperature
Complex Wave Numbers in the Vicinity of the Schwarzschild Event Horizon
This paper is devoted to investigate the cold plasma wave properties outside
the event horizon of the Schwarzschild planar analogue. The dispersion
relations are obtained from the corresponding Fourier analyzed equations for
non-rotating and rotating, non-magnetized and magnetized backgrounds. These
dispersion relations provide complex wave numbers. The wave numbers are shown
in graphs to discuss the nature and behavior of waves and the properties of
plasma lying in the vicinity of the Schwarzschild event horizon.Comment: 21 pages, 9 figures, accepted for publication Int. J. Mod. Phys.
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