How Saturated are Absorption Lines in the Broad Absorption Line Quasar PG 1411+442 ?

Recently, convincing evidence was found for extremely large X-ray absorption by column densities $> 10^{23} cm^{-2}$ in broad absorption line quasars. One consequence of this is that any soft X-ray emission from these QSOs would be the scattered light or leaked light from partially covering absorbing material. A detection of the unabsorbed soft X-ray and absorbed hard X-ray compo nent will allow to determine the total column density as well as the effective covering factor of the absorbing material, which can be hardly obtained from the UV absorption lines. Brinkmann et al. (1999) showed that both the unabsorbed and absorbed components are detected in the nearby very bright broad absorption line quasar PG 1411+442. In this letter, we make a further analysis of the broad band X-ray spectrum and the UV spectrum from HST, and demonstrate that broad absorption lines are completely saturated at the bottom of absorption troughs.Comment: 6 pages, 3 postscript figures. to appear in Astrophy. J. Letter

Magnetic spin excitations in diluted ferromagnetic systems: the case of Ga1−xMnxAsGa_{1-x}Mn_{x}As

We propose a theory which allow to calculate the magnetic excitation spectrum in diluted ferromagnetic systems. The approach is rather general and based on the Self-Consistent local Random Phase Approximation in which disorder (dilution) and thermal fluctuations are properly treated. To illustrate its reliability and accuracy we calculate the magnetic excitation in the diluted III-V magnetic semiconductor $Ga_{1-x}Mn_{x}As$. It is shown that dilution has a drastic effect on the excitation spectrum, indeed well defined magnon excitations exist only in a small region of the Brillouin zone centered around the $\Gamma$ point. We also calculate the spin stiffness in optimally annealed sample as a function of $Mn^{2+}$ concentration. A comparison to available measurements is done. We find a very good agreement for both the Curie temperature and the spin stiffness measured in well annealed samples and provide a plausible explanation for the very small values measured in as grown samples.Comment: The manuscript has been modified, 4 figures are included. Accepted for publication in Eur. Phys. Let

Phase transition from hadronic matter to quark matter

We study the phase transition from nuclear matter to quark matter within the SU(3) quark mean field model and NJL model. The SU(3) quark mean field model is used to give the equation of state for nuclear matter, while the equation of state for color superconducting quark matter is calculated within the NJL model. It is found that at low temperature, the phase transition from nuclear to color superconducting quark matter will take place when the density is of order 2.5$\rho_0$ - 5$\rho_0$. At zero density, the quark phase will appear when the temperature is larger than about 148 MeV. The phase transition from nuclear matter to quark matter is always first order, whereas the transition between color superconducting quark matter and normal quark matter is second order.Comment: 18 pages, 11 figure

Forward Neutral Pion Production in p + p and d + Au Collisions at √s_(NN) = 200 GeV

Measurements of the production of forward π^0 mesons from p + p and d + Au collisions at √s_(NN) = 200  GeV are reported. The p + p yield generally agrees with next-to-leading order perturbative QCD calculations. The d + Au yield per binary collision is suppressed as η increases, decreasing to ~30% of the p + p yield at =4.00, well below shadowing expectations. Exploratory measurements of azimuthal correlations of the forward π^0 with charged hadrons at η ≈ 0 show a recoil peak in p + p that is suppressed in d + Au at low pion energy. These observations are qualitatively consistent with a saturation picture of the low-x gluon structure of heavy nuclei

Liquid-gas phase transition in nuclear matter including strangeness

We apply the chiral SU(3) quark mean field model to study the properties of strange hadronic matter at finite temperature. The liquid-gas phase transition is studied as a function of the strangeness fraction. The pressure of the system cannot remain constant during the phase transition, since there are two independent conserved charges (baryon and strangeness number). In a range of temperatures around 15 MeV (precise values depending on the model used) the equation of state exhibits multiple bifurcates. The difference in the strangeness fraction $f_s$ between the liquid and gas phases is small when they coexist. The critical temperature of strange matter turns out to be a non-trivial function of the strangeness fraction.Comment: 15 pages, 7 figure

Directed flow in Au + Au collisions at √s_(NN) = 62.4 GeV

We present the directed flow (v1) measured in Au+Au collisions at √s_(NN) = 62.4 GeV in the midpseudorapidity region |η| < 1.3 and in the forward pseudorapidity region 2.5 < |η| < 4.0. The results are obtained using the three-particle cumulant method, the event plane method with mixed harmonics, and for the first time at the Relativistic Heavy Ion Collider, the standard method with the event plane reconstructed from spectator neutrons. Results from all three methods are in good agreement. Over the pseudorapidity range studied, charged particle directed flow is in the direction opposite to that of fragmentation neutrons

Competing Quantum Orderings in Cuprate Superconductors: A Minimal Model

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra.Comment: 5 pages, 4 eps included figure