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Singularities and Entropy in Bulk Viscosity dark energy Model

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Communications in Theoretical Physics 2011年第11期56卷 957-966页

作者：孟新河窦旭 Department of Physics Nankai University Kavli Institute of Theoretical Physics China Chinese Academy of Sciences

In this paper bulk viscosity is introduced to describe the effects of cosmic non-perfect fluid on the cosmos evolution and to build the unified dark energy （DE） with （dark） matter models. Also we derive a general relation between the bulk viscosity form and Hubble parameter that can provide a procedure for the viscosity DE model building. Especially, a redshift dependent viscosity parameter ζ ∝ λ0 ＋λ1（1 ＋z）n proposed in the previous work [X.H. Meng and X. Dou, Commun. Theor. Phys. B2 （2009） 377] is investigated extensively in this present work. Further more we use the recently released supernova dataset （the Constitution dataset） to constrain the model parameters. In order to differentiate the proposed concrete dark energy models from the well known ACDM model, statefinder diagnostic method is applied to this bulk viscosity model, as a complementary to the Om parameter diagnostic and the deceleration parameter analysis performed by us before. The DE model evolution behavior and tendency are shown in the plane of the statefinder diagnostic parameter pair {τ, s} as axes where the fixed point represents the A CDM model The possible singularity property in this bulk viscosity cosmology is also discussed to which we can conclude that in the different parameter regions chosen properly, this concrete viscosity DE model can have various late evolution behaviors and the late time singularity could be avoided. We also calculate the cosmic entropy in the bulk viscosity dark energy frame, and find that the total entropy in the viscosity DE model increases monotonously with respect to the scale factor evolution, thus this monotonous increasing property can indicate an arrow of time in the universe evolution, though the quantum version of the arrow of time is still very puzzling.

关键词： dark energy cosmology bulk viscosity unification of dark matter and dark energy

Friedmann Cosmology with Bulk Viscosity:A Concrete Model for dark energy

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Communications in Theoretical Physics 2009年第8期52卷 377-382页

作者： MENG Xin-He D0U Xu Department of Physics Nankai University Tianjin 300071 China Kavli Institute for Theoretical Physics China at the Chinese Academy of Sciences （KITPC-CAS） Beijing 100190 China

The universe content is considered as a non-perfect fluid with bulk viscosity and can be described by a general equation of state （endowed some deviation from the conventionally assumed cosmic perfect fluid model）. An explicitly bulk viscosity dark energy model is proposed to confront consistently with the current observational data sets by statistical analysis and is shown consistent with （not deviated away much from） the concordant A Cold dark matter （CDM） model by comparing the decelerating parameter. Also we compare our relatively simple viscosity dark energy model with a more complicated one by contrast with the concordant ACDM model and find our model improves for the viscosity dark energy model building. Finally we discuss the perspectives of dark energy probes for the coming years with observations.

关键词： dark energy cosmology bulk viscosity unification of dark matter and dark energy

Comparing the VGCG model as the unification of dark sectors with observations

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Science China(Physics,Mechanics & Astronomy) 2014年第4期57卷 796-800页

作者： LU JianBo CHEN LiDong XU LiXin LI TianQiang Department of Physics Liaoning Normal University Jilin Radio and TV University School of Physics and Optoelectronic Technology Dalian University of Technology

Current observations indicate that 95% of the energy density in the universe is the unknown dark *** dark component is considered composed of two fluids:dark matter and dark *** it is a mixture of these two dark components,i.e.,one can consider it an exotic unknown dark *** this consideration,the variable generalized Chaplygin gas(VGCG)model is studied with not dividing the unknown fluid into dark matter and dark energy parts in this *** using the Markov Chain Monte Carlo method,the VGCG model as the unification of dark sectors is constrained,and the constraint results on the VGCG model parameters are,n=0.00057+0.0001+0.0009-0.0006-0.0006,α=0.0015+0.0003+0.0017-0.0015-0.0015and B s=0.778+0.016+0.030-0.016-0.035,obtained by the cosmic microwave background data from the 7-year WMAP full data points,the baryon acoustic oscillation data from Sloan Digital Sky Survey(SDSS)and 2-degree Field Galaxy Redshift(2dFGRS)survey,and the Union2 type Ia supernova data with systematic *** last,according to the evolution of deceleration parameter it is shown that an expanded universe from deceleration to acceleration can be obtained in VGCG cosmology.

关键词： variable generalized Chaplygin gas(VGCG) unification of dark matter and dark energy cosmic constraints