714 research outputs found

### Hadron production in relativistic nuclear collisions: thermal hadron source or hadronizing quark-gluon plasma?

Measured hadron yields from relativistic nuclear collisions can be equally
well understood in two physically distinct models, namely a static thermal
hadronic source vs.~a time-dependent, nonequilibrium hadronization off a
quark-gluon plasma droplet. Due to the time-dependent particle evaporation off
the hadronic surface in the latter approach the hadron ratios change (by
factors of $<\approx 5$) in time. Final particle yields reflect time averages
over the actual thermodynamic properties of the system at a certain stage of
the evolution. Calculated hadron, strangelet and (anti-)cluster yields as well
as freeze-out times are presented for different systems. Due to strangeness
distillation the system moves rapidly out of the T, $\mu_q$ plane into the
$\mu_s$-sector. Strangeness to baryon ratios f_s=1-2 prevail during a
considerable fraction (50%) of the time evolution (i.e. $\Lambda$-droplets or
even $\Xi^-$-droplets form the system at the late stage: The possibility of
observing this time evolution via HBT correlations is discussed). The observed
hadron ratios require $T_c\approx 160 MeV$ and $B^{1/4}>\approx 200 MeV$. If
the present model is fit to the extrapolated hadron yields, metastable
hypermatter can only be produced with a probability $p< 10^{-8}$ for $A \ge 4$.Comment: Submitted to Z. Phys.

### Parity Doublet Model applied to Neutron Stars

The Parity doublet model containing the SU(2) multiplets including the
baryons identified as the chiral partners of the nucleons is applied for
neutron star matter. The chiral restoration is analyzed and the maximum mass of
the star is calculated.Comment: Proceeding to the conference International Symposium on Exotic States
of Nuclear Matte

### Fast Dynamical Evolution of Hadron Resonance Gas via Hagedorn States

Hagedorn states are the key to understand how all hadrons observed in high
energy heavy ion collisions seem to reach thermal equilibrium so quickly. An
assembly of Hagedorn states is formed in elementary hadronic or heavy ion
collisions at hadronization. Microscopic simulations within the transport model
UrQMD allow to study the time evolution of such a pure non-equilibrated
Hagedorn state gas towards a thermally equilibrated Hadron Resonance Gas by
using dynamics, which unlike strings, fully respect detailed balance.
Propagation, repopulation, rescatterings and decays of Hagedorn states provide
the yields of all hadrons up to a mass of m=2.5 GeV. Ratios of feed down
corrected hadron multiplicities are compared to corresponding experimental data
from the ALICE collaboration at LHC. The quick thermalization within t=1-2 fm\c
of the emerging Hadron Resonance Gas exposes Hagedorn states as a tool to
understand hadronization.Comment: 5 pages, 7 figures, 1 tabl

### In-medium properties of D-mesons at FAIR

We obtain the D-meson spectral density at finite temperature for the
conditions of density and temperature expected at FAIR. We perform a
self-consistent coupled-channel calculation taking, as a bare interaction, a
separable potential model. The $\Lambda_c$ (2593) resonance is generated
dynamically. We observe that the D-meson spectral density develops a sizeable
width while the quasiparticle peak stays close to the free position. The
consequences for the D-meson production at FAIR are discussed.Comment: 4 pages, 3 figures, to appear in the proceedings of 9th International
Conference on Hypernuclear and Strange Particle Physics (HYP2006), Mainz
(Germany), 10-14 October 200

### Covariant Canonical Gauge theory of Gravitation resolves the Cosmological Constant Problem

The covariant canonical transformation theory applied to the relativistic
theory of classical matter fields in dynamic space-time yields a new (first
order) gauge field theory of gravitation. The emerging field equations embrace
a quadratic Riemann curvature term added to Einstein's linear equation. The
quadratic term facilitates a momentum field which generates a dynamic response
of space-time to its deformations relative to de Sitter geometry, and adds a
term proportional to the Planck mass squared to the cosmological constant. The
proportionality factor is given by a dimensionless parameter governing the
strength of the quadratic term. In consequence, Dark Energy emerges as a
balanced mix of three contributions, (A)dS curvature plus the residual vacuum
energy of space-time and matter. The Cosmological Constant Problem of the
Einstein-Hilbert theory is resolved as the curvature contribution relieves the
rigid relation between the cosmological constant and the vacuum energy density
of matter

### New Physics at the International Facility for Antiproton and Ion Research (FAIR) Next to GSI

The project of the international Facility for Antiproton and Ion Research
(FAIR), co-located to the GSI facility in Darmstadt, has been officially
started on November 7, 2007. The current plans of the facility and the planned
research program will be described. An investment of about 1 billion euro will
permit new physics programs in the areas of low and medium energy antiproton
research, heavy ion physics complementary to LHC, as well as in nuclear
structure and astrophysics. The facility will comprise about a dozen
accelerators and storage rings, which will enable simultaneous operations of up
to four different beams.Comment: 7 pages, 1 figure. Invited Talk presented at the "Fourth
International Conference on Fission and Properties of Neutron-Rich nuclei",
held at Sanibel Island, Florida, November 11-17, 200

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