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.
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.
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.
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.
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.