5906222
Coincidence problem in an oscillating universe
We analyze an oscillating universe model in brane world cenario. The oscillating universe cycles through a series of expansions and contractions and its energy density is dominated by dust matter at early-time expansion phase and by phantom dark energy at late-time expansion phase. We find that the period of the oscillating universe is not sensitive to the tension of the brane, but sensitive to the equation-of-state parameter w of the phantom dark energy, and the ratio of the period to the current Hubble age approximately varies from 3 to 9 when the parameter w changes from −1.4 to −1.1. The fraction of time that the oscillating universe spends in the coincidence state is also comparable to the period of the oscillating universe. This result indicates that the coincidence problem can be significantly ameliorated in the oscillating universe without singularity.
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.
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.
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.
197512779
Stable Gravastars of Phantom Energy
119819008
Large angle elastic and inelastic scattering of protons from Ca 40 at 800 MeV
Measurements are reported for the elastic and inelastic scattering of 800 MeV protons from $^{40}\mathrm{Ca}$. Differential cross sections were measured out to 42\ifmmode^\circ\else\textdegree\fi{} while analyzing powers were obtained out to 30\ifmmode^\circ\else\textdegree\fi{}. The angular distributions are diffractive in character at all angles. Theoretical analysis of the data was carried out in the framework of the diffraction multiple scattering theory. The following results were obtained: (i) Diffraction multiple scattering theory reproduces the data qualitatively out to the large momentum transfers. (ii) For the ground state density distribution ${〈{{r}_{p}}^{2}〉}^{\frac{1}{2}}\ensuremath{-}{〈{{r}_{n}}^{2}〉}^{\frac{1}{2}}=0.142\ifmmode\pm\else\textpm\fi{}0.075$ fm is obtained and the analysis favors the value of the correlation length ${\ensuremath{\xi}}_{c}=\ensuremath{-}0.5$ fm. (iii) The excitation of the lowest-lying collective states (${3}^{\ensuremath{-}}$, ${5}^{\ensuremath{-}}$, ${2}^{+}$) was analyzed using one-phonon excitation macroscopic parameters. The values of the ${\ensuremath{\beta}}_{2}$, ${\ensuremath{\beta}}_{3}$, ${\ensuremath{\beta}}_{5}$ parameters obtained agree quantitatively with lower energy ($p$,${p}^{\ensuremath{'}}$) scattering results.
123099584
Cross sections and analyzing powers in the (p,d) reaction around 500 MeV
Abstract Cross sections and analyzing powers for the (p,d) reaction on 12 C, 13 C and 28 Si are measured around 500 MeV. DWBA calculations are found to reproduce the main features of the (p,d) data, when proton potentials are used which give strong oscillations in the (p,p) analyzing powers as required by the elastic data. Damping of the nuclear interior contribution is unimportant at this 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.
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.