Browsing by Author "Viollier, Raoul"

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    Finite size corrections to the equation of state for nuclear matter near the phase transition hadron gas to quark gluon plasma
    (1988) Schnabel, Allard Guntram; Rafelski, Jan; Viollier, Raoul
    It is widely accepted that the finite size of the hadrons must be taken into account in a thermodynamic description of the hadron gas near the phase transition to quark gluon plasma. Existing thermodynamic models introducing a .correction due to the finite size of the particles are reviewed and discussed. A new model to describe dense nuclear matter is developed. The model takes into account the different quantum statistical distributions of the hadrons. The grand canonical pressure partition function is used. to obtain the thermodynamic limit. The grand canonical partition function is restricted so that only those states where the extended particles fit into the volume of the system, are counted. The configuration space is reduced accordingly. The hadrons are described as MIT bags. The size of the particles depends on the pressure in the system. The pressure in the system compresses the hadrons which leads to an increase of the mass of the hadrons according to the MIT bag equation. The size of the particles is determined by the minimum of the grand canonical potential. A consistent thermodynamic theory is obtained. The equation of state for hadronic matter is discussed for the special cases, zero temperature and zero chemical potential, before the general case of finite temperature and finite chemical potential is used to construct a first order phase transition from hadron gas to quark gluon plasma. At high densities the influence of the description of the hadrons as MIT bags becomes significant. It is found that the phase transition is strongly dependent on the value chosen for the bag constant and the application of as corrections. Therefore ~reliable value of the bag constant and a generally accepted theory for as corrections are essential to obtain a good thermodynamic description of the phase transition from hadron gas to quark gluon plasma.
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    The motion of stars and the accretion of matter in the fermion ball and black hole scenarios of the galactic centre
    (2003) Halliday, Samuel James Alexander; Viollier, Raoul
    The motion of stars SO-I, SO-2 and SO-4, in the vicinity of the galactic centre, is investigated using a X2 analysis of the parameters in our line of sight. The resulting phase spaces for the black hole and fermion ball scenarios are compared. We find that due to the lack of accurate z or Vz data, the upper limit of required observational time to discriminate between the scenarios is of the order 30 to 40 years. Such z and Vz data might allow us to eliminate one of the scenarios immediately. The spectrum from the Sgr A * region is also investigated using a simple Newtonian, optically thick and geometrically thin model for each scenario. As has already been known for some time, this technique is not applicable to a possible black hole scenario at Sgr A * and as a consequence, is incapable of explaining a cut-off in the spectrum at around 1013Hz. This cut-off follows naturally from the fermion ball potential distribution in this simple model. It should be noted that Advection Dominated Accretion Flow models (not investigated here) are able to predict the observed spectrum for the black hole scenario.