119300132
Constraining the lattice fluid dark energy from SNe Ia, BAO and OHD
Sanchez and Lacombe have developed a lattice fluid theory based on a well-defined statistical mechanical model. Taking the lattice fluid as a candidate of dark energy, we investigate the cosmic evolution of this fluid. Using the combined observational data of Type Ia Supernova (SNe Ia) Union2.1, Baryon Acoustic Oscillations (BAO) data from 6dFGS, SDSS and WiggleZ survey, and Observational Hubble Data (OHD), we find the best fit value of the parameters: A = −0.3 ± 0.2(1σ) ± 0.4(2σ) ± 0.8(3σ) and Ωm = 0.31 ± 0.02(1σ) ± 0.05(2σ) ± 0.07(3σ). The cosmological implications of the model are presented.
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.
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.
118404612
When scalar field is kinetically coupled to the Einstein tensor
We explore the cosmic evolution of a scalar field with the kinetic term coupled to the Einstein tensor. We find that, in the absence of other matter sources or in the presence of only pressureless matter, the scalar behaves as pressureless matter and the sound speed of the scalar is vanishing. These properties enable the scalar field to be a candidate of cold dark matter. By also considering the scalar potential, we find the scalar field may play the role of both dark matter and dark energy. In this case, the equation of state of the scalar can cross the phantom divide, but this can lead to the sound speed becoming superluminal as it crosses the divide, and so is physically forbidden. Finally, if the kinetic term is coupled to more than one Einstein tensor, we find the equation of state is always approximately equal to -1 whether the potential is flat or not, and so the scalar may also be a candidate for the inflaton.
119198146
Introduction of the generalized Lorentz gauge condition into the vector-tensor theory
We introduce the generalized Lorentz gauge condition in the theory of quantum electrodynamics into the general vector-tensor theories of gravity. Then we explore the cosmic evolution and the static, spherically symmetric solution of the four dimensional vector field with the generalized Lorenz gauge. We find that, if the vector field is minimally coupled to the gravitation, it behaves as the cosmological constant. On the other hand, if it is nonminimally coupled to the gravitation, the vector field could behave as vast matters in the background of the spatially flat Friedmann-Robertson-Walker Universe. But it may not be the case. The weak, strong and dominant energy conditions, the stability analysis of classical and quantum aspects would put constraints on the parameters and so the equation of state of matters would be greatly constrained.
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.
108059264
An active terminating pre-amplifier for delay line readout systems
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.
56119429
Centrality dependence of particle production in p-Pb collisions at $\sqrt{s_{\rm NN} }$= 5.02 TeV
We report measurements of the primary charged-particle pseudorapidity density and transverse momentum distributions in p-Pb collisions at sNN=5.02TeV and investigate their correlation with experimental observables sensitive to the centrality of the collision. Centrality classes are defined by using different event-activity estimators, i.e., charged-particle multiplicities measured in three different pseudorapidity regions as well as the energy measured at beam rapidity (zero degree). The procedures to determine the centrality, quantified by the number of participants (Npart) or the number of nucleon-nucleon binary collisions (Ncoll) are described. We show that, in contrast to Pb-Pb collisions, in p-Pb collisions large multiplicity fluctuations together with the small range of participants available generate a dynamical bias in centrality classes based on particle multiplicity. We propose to use the zero-degree energy, which we expect not to introduce a dynamical bias, as an alternative event-centrality estimator. Based on zero-degree energy-centrality classes, the Npart dependence of particle production is studied. Under the assumption that the multiplicity measured in the Pb-going rapidity region scales with the number of Pb participants, an approximate independence of the multiplicity per participating nucleon measured at mid-rapidity of the number of participating nucleons is observed. Furthermore, at high-pT the p-Pb spectra are found to be consistent with the pp spectra scaled by Ncoll for all centrality classes. Our results represent valuable input for the study of the event-activity dependence of hard probes in p-Pb collisions and, hence, help to establish baselines for the interpretation of the Pb-Pb data.