119528492
Thermodynamics and stability of hyperbolic charged black holes
In AdS space the black hole horizon can be a hypersurface with a positive, zero, or negative constant curvature, resulting in different horizon topology. Thermodynamics and stability of black holes in AdS spaces are quite different for different horizon curvatures. In this paper we study thermodynamics and stability of hyperbolic charged black holes with negative constant curvature horizon in the grand canonical ensemble and canonical ensemble, respectively. They include hyperbolic Reissner-Nordstrom black holes in arbitrary dimensions and hyperbolic black holes in the D=5,4,7 gauged supergravities. It is found that associated Gibbs free energies are always negative, which implies that these black hole solutions are globally stable and the black hole phase is dominant in the grand canonical ensemble, but there is a region in the phase space where the black hole is not locally thermodynamically stable with a negative heat capacity for a given gauge potential. In the canonical ensemble, the Helmholtz free energies are not always negative and heat capacities with fixed electric charge are not always positive, which indicates that the Hawking-Page phase transition may happen and black holes are not always locally thermodynamically stable.
27386290
Dynamics of plane-symmetric thin walls in general relativity.
Plane walls (including plane domain walls) without reflection symmetry are studied in the framework of Einstein's general relativity. Using the distribution theory, all the Einstein field equations and Bianchi identities are split into two groups: one holding in the regions outside of the wall and the other holding at the wall. The Einstein field equations at the wall are found to take a very simple form, and given explicitly in terms of the discontinuities of the metric coefficients and their derivatives. The Bianchi identities at the wall are also given explicitly. Using the latter, the interaction of a plane wall with gravitational waves and some specific matter fields is studied. In particular, it is found that, when a gravitational plane wave passes through a wall, if the wall has no reflection symmetry, the phenomena, such as reflection, stimulation, or absorption, in general, occur. It is also found that, unlike for gravitational waves, a massless scalar wave or an electromagnetic wave continuously passes through a wall without any reflection. The repulsion and attraction of a plane wall are also studied. It is found that the acceleration of an observer who is at rest relative to the wall usually consists of threemore » parts: one is due to the force produced by the wall, the second is due to the force produced by the space-time curvature, which is zero if the wall has reflection symmetry, and the last is due to the accelerated motion of the wall. As a result, a repulsive (attractive) plane wall may not be repulsive (attractive) at all. Finally, the collision and interaction among the walls are studied.« less
3041179
Instability of cosmological event horizons of nonstatic global cosmic strings
The stability of the cosmological event horizons found recently by Gregory [Phys. Rev. D54, 4955 (1996)] for a class of non-static global cosmic strings is studied. It is shown that they are not stable to both test particles and physical perturbations. In particular, the back reaction of the perturbations of null dust fluids will turn them into spacetime singularities. The resulted singularities are strong in the sense that the distortion of test particles diverges logarithmically when these singular hypersurfaces are approaching.
1241582
Generalized Milne Space, Eternal Accelerating Cosmology, Ep-branes and dS/CFT Correspondence
This paper has been withdrawn by the authors due to the existence of main results in the literature.
119100887
Direct evidence of acceleration from a distance modulus–redshift graph
The energy conditions give upper bounds on the luminosity distance. We apply these upper bounds to the 192 ESSENCE supernova Ia data to show that the Universe has experienced accelerated expansion. This conclusion is drawn directly from the distance modulus - redshift graph. In addition to being a very simple method, this method is also totally independent of any cosmological model. From the degeneracy of the distance modulus at low redshift, we argue that the choice of omega(0) for probing the property of dark energy is misleading. One explicit example is used to support this argument.
26320238
Collapsing perfect fluid in higher-dimensional spherical spacetimes
The general metric for N -dimensional spherically symmetric and conformally flat spacetimes is given, and all the homogeneous and isotropic solutions for a perfect fluid with the equation of state p = αρ are found. These solutions are then used to model the gravitational collapse of a compact ball. It is found that when the collapse has continuous self-similarity, the formation of black holes always starts with zero mass, and when the collapse has no such symmetry, the formation of black holes always starts with a mass gap.
121101159
Effect of a preshower detector on calorimetry performance
Abstract Test beam results obtained with a preshower detector in a SDC calorimetry configuration are presented. The benefits of independently instrumenting the first scintillating tile of each tower of the tile/fiber electromagnetic calorimeter, forming the analogue of the “Massless Gap” in LAr calorimeters, are demonstrated. Electron and pion data were taken with a calorimeter configured with one or two radiation lengths of inert material in front, a scintillating fiber preshower detector, a tile/fiber electromagnetic calorimeter, a shower maximum detector, and a tile/fiber hadron calorimeter. The energy deposited in the scintillating fibers of the preshower detector was summed to simulate the preshower energy that would be detected by the first scintillating tile of an EMC tower. The data were collected in the MP9 beam line at Fermilab during the Summer and Fall of 1991. The relative degradation in electromagnetic energy resolution due to the inert material in front of the electromagnetic calorimeter was measured. The resolution is improved by adding in the properly weighted preshower energy. The charged pion rejection versus electron acceptance is presented for combined cuts using the electromagnetic and hadronic calorimeters, with the energy deposited in the preshower and shower maximum detectors. We show that, even after calorimetric and shower maximum cuts, the pion rejection is further improved by using the preshower energy.
5973680
Shear-free radiating collapse and conformal flatness
Here we study some general properties of spherical shear-free collapse. Its general solution when imposing conformal atness is re-obtained (Refs. 1 and 2) and matched to the outgoing Vaidya spacetime. We propose a simple model satisfying these conditions and study its physical consequences. Special attention deserve, the role played by relaxational processes and the conspicuous link betweeen dissipation and density inhomogeneity.
120198608
Differential cross sections and analyzing powers for pp elastic scattering at 1. 46 GeV/c in the Coulomb-nuclear interference region
Differential cross sections sigma(theta) and analyzing powers A(theta) for pp elastic scattering have been measured in the Coulomb-nuclear interference region at 800 MeV. The measurements, which extend down to 0.5 deg in the laboratory, have been analyzed to deduce the zero-degree pp scattering amplitudes. The ratio rho of the real to imaginary parts of the spin-independent amplitude was found to be -0.04 +- 0.04; the contribution of the double-spin-flip amplitudes to sigma(0) was found to be 0.16 +- 0.03 times that of the spin-independent amplitude; while the ratios of the imaginary and real parts of the single spin-flip amplitude to sintheta were found to be 0.74 +- 0.04 and -0.03 +- 0.08 fm, respectively. Except for the last, these experimental values agree with the predictions of forward dispersion relations and phase shift analyses.
118411966
Elastic Scattering of Positive Kaons on Polarized Deuterons at 1.5 Gev/c.
81234
Levi-Civita solutions coupled with electromagnetic fields
The local and global properties of the Levi-Civita (LC) solutions coupled with an electromagnetic field are studied and some limits to the vacuum LC solutions are given, from which the physical and geometrical interpretations of the free parameters involved in the solutions are made clear. Sources for both the LC vacuum solutions and the LC solutions coupled with an electromagnetic field are studied, and in particular it is found that all the LC vacuum solutions with σ ≥ 0 can be produced by cylindrically symmetric thin shells that satisfy all the energy conditions, weak, dominant and strong. When the electromagnetic field is present, the situation changes dramatically. In the case of a purely magnetic field, all the solutions can be produced by physically acceptable cylindrical thin shells, while in the case of a purely electric field, no such shells are found for any choice of the free parameters involved in the solutions.