119265980
Scalar Field, Four Dimensional Spacetime Volume and the Holographic Dark Energy
We explore the cosmic evolution of a scalar field which is identified with the four dimensional spacetime volume. Given a specific form for the Lagrangian of the scalar field, a new holographic dark energy model is present. The energy density of dark energy is reversely proportional to the square of the radius of the cosmic null hypersurface which is present as a new infrared cutoff for the Universe. We find this holographic dark energy belongs to the phantom dark energy for some appropriate parameters in order to interpret the current acceleration of the Universe.
119284599
Cosmological models with Lagrange multiplier field
We first consider the Einstein-aether theory with a gravitational coupling and a Lagrange multiplier field, and then consider the non-minimally coupled quintessence field theory with Lagrange multiplier field. We study the influence of the Lagrange multiplier field on these models. We show that the energy density evolution of the Einstein-aether field and the quintessence field are significantly modified. The energy density of the Einstein-aether is nearly a constant during the entire history of the Universe. The energy density of the quintessence field can also be kept nearly constant in the matter dominated Universe, or even exhibit a phantom-like behavior for some models. This suggests a possible dynamical origin of the cosmological constant or dark energy. Further more, for the canonical quintessence in the absence of gravitational coupling, we find that the quintessence scalar field can play the role of cold dark matter with the introduction of a Lagrange multiplier field. We conclude that the Lagrange multiplier field could play a very interesting and important role in the construction of cosmological models. (C) 2011 Elsevier B.V. All rights reserved.
118647873
Cyclic universe due to phantom and quintessence
We explore a cyclic universe due to phantom and quintessence fields. We find that, in every cycle of the evolution of the universe, the phantom dominates the cosmic early history and quintessence dominates the cosmic far future. In this model of universe, there are infinite cycles of expansion and contraction. Different from the inflationary universe, the corresponding cosmic space-time is geodesically complete and quantum stable. But similar to the Cyclic Model, the flatness problem, the horizon problem and the large scale structure of the universe can be explained in this cyclic universe.
118396278
Does the mass of a black hole decrease due to the accretion of phantom energy
According to Babichev et al., the accretion of a phantom test fluid onto a Schwarzschild black hole will induce the mass of the black hole to decrease, however the backreaction was ignored in their calculation. Using new exact solutions describing black holes in a background Friedmann-Robertson-Walker universe, we find that the physical black hole mass may instead increase due to the accretion of phantom energy. If this is the case, and the future universe is dominated by phantom dark energy, the black hole apparent horizon and the cosmic apparent horizon will eventually coincide and, after that, the black hole singularity will become naked in finite comoving time before the big rip occurs, violating the cosmic censorship conjecture.
16437663
Unified dark energy and dark matter from a scalar field different from quintessence
We explore unification of dark matter and dark energy in a theory containing a scalar field of non-Lagrangian type, obtained by direct insertion of a kinetic term into the energy-momentum tensor. This scalar is different from quintessence, having an equation of state between -1 and 0 and a zero sound speed in its rest frame. We solve the equations of motion for an exponential potential via a rewriting as an autonomous system, and demonstrate the observational viability of the scenario, for sufficiently small exponential potential parameter lambda, by comparison to a compilation of kinematical cosmological data.
117041935
Phenomenological Models of dark Energy
As is well known, we are now confronted with a coincidence problem for dark energy, namely, why do we happen to live at a special epoch in which the dark energy density and the dark matter density are comparable? This problem becomes very much sharp especially for the cosmological constant as the dark energy candidate. In order to resolve this cosmological coincidence problem, here we construct two phenomenological cosmology models in which the Universe is made of matter (baryon and dark matter), radiation, and a perfect fluid (playing the role of dark energy). It is shown that the density of the perfect fluid always traces the density of matter in orders in the history of the Universe. Thus the coincidence problem is greatly relaxed.
121733272
Coherence effects on two-pion interferometry in ultra-high energy heavy-ion collisions
Abstract The effects of two kinds of coherent lengths, the wave packet length of the emitter and the radius of the coherent source, on two-pion interferometry are studied. It is shown that both coherent lengths can decrease the apparent radius of the source and cause abundant pions at low momentum.
108059264
An active terminating pre-amplifier for delay line readout systems
120380312
Pion-interferometry analysis in relativistic heavy-ion collisions based on the VENUS model☆
Abstract The source size in relativistic heavy-ion collisions obtained by pion-interferometry analyses based on the VENUS model is compared with the actual source size of the model and experimental measurements. The predicted transverse source size is larger than the size of the projectile nuclei, but smaller than the preliminary findings from a recent experiment in the central rapidity region. The effect of rescattering on the source size is also discussed.