119317806
Current constraints on interacting holographic dark energy
Abstract Although there is mounting observational evidence that the cosmic expansion is undergoing a late-time acceleration, the physical mechanism behind such a phenomenon is yet unknown. In this Letter, we investigate a holographic dark energy (HDE) model with interaction between the components of the dark sector in the light of current cosmological observations. We use both the new gold sample of 182 type Ia supernovae (SNe Ia) and the 192 SNe Ia ESSENCE data, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey and the shift parameter from the three-year Wilkinson Microwave Anisotropy Probe data. In agreement with previous results, we show that these observations suggest a very weak coupling or even a noninteracting HDE. The phantom crossing behavior in the context of these scenarios is also briefly discussed.
119227824
Cosmological constant and late transient acceleration of the universe in the Horava-Witten Heterotic M-Theory on S^{1}/Z_{2}
Abstract Orbifold branes are studied in the framework of the 11-dimensional Horava–Witten heterotic M-theory. It is found that the effective cosmological constant can be easily lowered to its current observational value by the mechanism of large extra dimensions. The domination of this constant over the evolution of the universe is only temporary. Due to the interaction of the bulk and the branes, the universe will be in its decelerating expansion phase again in the future, whereby all problems connected with a far future de Sitter universe are resolved.
2444705
Gravitational and particle radiation from long cosmic strings
Gravitational and massless particle radiation from infinitely long cosmic strings with finite thickness is studied by constructing analytic solutions to the Einstein field equations with certain forms of energy - momentum tensor. Using Thorne's -energy arguments, it is shown that the radiation always carries away energy. As a result, the angle defect outside the string is less than that in the non-radiation case. Since the solutions are exact, the back reaction of the radiation is automatically taken into account. In fact, it is shown that because of this back reaction the spacetime is always singular on the symmetry axis. The singularity is a scalar one and not removable.
109935503
No-Go theorem in spacetimes with two commuting spacelike killing vectors
Four-dimensional Riemannian spacetimes with two commuting spacelike Killing vectors are studied in Einstein's theory of gravity, and found that no outer apparent horizons exist, provided that the dominant energy condition holds.
119168760
Homothetic self-similar solutions of three-dimensional Brans-Dicke gravity
All homothetic self-similar solutions of the Brans-Dicke scalar field in three-dimensional spacetime with circular symmetry are found in closed form.
10393301
On the sources of static plane symmetric vacuum space-times
Abstract The sources of static vacuum plane space-times with reflection symmetry are considered. It is argued that the counterpart of the Einstein theory to the gravitational field of a massive Newtonian plane should be described by the Rindler solution, which represents also a uniform gravitational field, and the test particles moving in which have constant accelerations.
117264492
Reply to Comment of Gazdzicki and Heinz on Strangeness Enhancement in $p+A$ and $S+A$
The Comment of Gazdzicki and Heinz is flawed because their assumed baryon stopping power in $pA$ is inconsistent with data and because they ignored half the analysis based on the VENUS model. The Comment continues the misleading presentation of strangeness enhancement by focusing on ratios of integrated yields. Those ratios discard essential experimental information on the rapidity dependence of produced $\Lambda$ and obscure discrepancies between different data sets. Our conclusion remains that the NA35 minimum bias data on $p+S\rightarrow\Lambda +X $ indicate an anomalous enhancement of central rapidity strangeness in few nucleon reactions that points to non-equilibrium dynamics as responsible for strangeness enhancement in nuclear reactions.
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.
120345656
Evidence for the noneikonal effects in the tensor and vector analyzing powers in p-d elastic scattering at 800 MeV☆
Abstract Deuteron tensor and vector analyzing powers have been measured for the first time in p- d elastic scattering at 800 MeV proton laboratory energy for a - t range between 0.032 and 1.038 (GeV/ c ) 2 . The data provide a very sensitive test of the multiple scattering theory at intermediate energies. The inclusion of the noneikonal correction in the Glauber diffraction theory is essential in the description of the data, especially for -t ⪆0.2 (GeV/ c 2 ), where discrepancies of up to 150% are observed with the theory based on the eikonal approximation.
881828
Search for small trans-Neptunian objects by the TAOS project
The Taiwan-America Occultation Survey (TAOS) aims to determine the number of small icy bodies in the outer reach of the Solar System by means of stellar occultation. An array of 4 robotic small (D=0.5 m), wide-field (f/1.9) telescopes have been installed at Lulin Observatory in Taiwan to simultaneously monitor some thousand of stars for such rare occultation events. Because a typical occultation event by a TNO a few km across will last for only a fraction of a second, fast photometry is necessary. A special CCD readout scheme has been devised to allow for stellar photometry taken a few times per second. Effective analysis pipelines have been developed to process stellar light curves and to correlate any possible flux changes among all telescopes. A few billion photometric measurements have been collected since the routine survey began in early 2005. Our preliminary result of a very low detection rate suggests a deficit of small TNOs down to a few km size, consistent with the extrapolation of some recent studies of larger (30-100 km) TNOs.
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.