4,092 research outputs found
What is so special about strangeness in hot matter?
The production of strange particles in a hot medium as produced in collisions
of heavy ions is considered one of the most important signals for the phase
transition to a quark-gluon plasma. In the first part of this lecture, the
theoretical description of strangeness production in hot matter is outlined for
a gas of quarks and gluons and for a hadronic gas and its impact on the
deconfinement phase transition. Then in the second part, constraints from the
underlying chiral symmetry of Quantum Chromodynamics (QCD) are utilized to
extract signals with strangeness for the chiral phase transition in hot matter.Comment: 22 pages, 9 figures, to be published as topical review for Journal of
Physics
Pulsar kicks by anisotropic neutrino emission from quark matter
We discuss an acceleration mechanism for pulsars out of their supernova
remnants based on asymmetric neutrino emission from quark matter in the
presence of a strong magnetic field. The polarized electron spin fixes the
neutrino emission from the direct quark Urca process in one direction along the
magnetic field. We calculate the magnetic field strength which is required to
polarize the electron spin as well as the required initial proto-neutron star
temperature for a successfull acceleration mechanism. In addition we discuss
the neutrino mean free paths in quark as well as in neutron matter which turn
out to be very small. Consequently, the high neutrino interaction rates will
wash out the asymmetry in neutrino emission. As a possible solution to this
problem we take into account effects from colour superconductivity.Comment: 6 pages, 3 figures, poster contribution at the conference "Nuclear
Physics in Astrophysics III",Dresden,March 26-31,200
Conditions for Phase Equilibrium in Supernovae, Proto-Neutron and Neutron Stars
We investigate the qualitative properties of phase transitions in a general
way, if not the single particle numbers of the system but only some particular
charges like e.g. baryon number are conserved. In addition to globally
conserved charges we analyze the implications of locally conserved charge
fractions, like e.g. local electric charge neutrality or locally fixed proton
or lepton fractions. The conditions for phase equilibrium are derived and it is
shown, that the properties of the phase transition do not depend on the locally
conserved fractions. Finally, the general formalism is applied to the
liquid-gas phase transition and the hadron-quark phase transition for typical
astrophysical environments like in supernovae, proto-neutron or a neutron
stars. We demonstrate that the Maxwell construction known from
cold-deleptonized neutron star matter with two locally charge neutral phases
requires modifications and further assumptions concerning the applicability for
hot lepton-rich matter. All possible combinations of local and global
conservation laws are analyzed, and the physical meaningful cases are
identified. Several new kinds of mixed phases are presented, as e.g. a locally
charge neutral mixed phase in proto-neutron stars which will disappear during
the cooling and deleptonization of the proto-neutron star.Comment: 18 page
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 (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
An LQR controller design approach for a Large Gap Magnetic Suspension System (LGMSS)
Two control approaches for a Large Gap Magnetic Suspension System (LGMSS) are investigated and numerical results are presented. The approaches are based on Linear Quadratic Regulator (LQR) control theory and include a nonzero set point regulator with constant disturbance input and an integral feedback regulator. The LGMSS provides five degree of freedom control of a cylindrical suspended element which is composed of permanent magnet material. The magnetic actuators are air core electromagnets mounted in a planar way
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