Since it can describe the rotation curves of galaxies without dark matter and can give rise to accelerated expansion, conformal gravity attracts much attention recently. As a theory of modified gravity, it is important to test conformal gravity with astrophysical observations. Here we constrain conformal gravity with SNIa and Hubble parameter data and investigate whether it suffers from an age problem with the age of APM~08279+5255. We find conformal gravity can accommodate the age of APM~08279+5255 at 3 $\sigma$ deviation, unlike most of dark energy models which suffer from an age problem.Comment: 6 pages, 2 figure
We apply the Statefinder hierarchy and the growth rate of matter perturbations to discriminate modified Chaplygin gas (MCG), generalized Chaplygin gas (GCG), superfluid Chaplygin gas (SCG), purely kinetic k-essence (PKK), and ΛCDM model. We plot the evolutional trajectories of these models in the statefinder plane and in the composite diagnostic plane. We find that GCG, MCG, SCG, PKK, and ΛCDM can be distinguished well from each other at the present epoch by using the composite diagnostic {ǫ(z), S(1) 5 }. Using other combinations, such as {S3 }, and {ǫ(z), S4}, some of these five dark energy models cannot be distinguished. PACS numbers: 95.36.+x, 98.80.Es
We investigate the evolution of the power law k-essence field in FRWL spacetime. The autonomous dynamical system and critical points are obtained. The corresponding cosmological parameters, such as Ω φ and w φ , are calculated at these critical points. We find it is possible to achieve an equation of state crossing through −1 for k-essence field. The results we obtained indicate that the power law k-essence dark energy model can be compatible with observations. PACS: 95.36.+x, 98.80.Es, 98.80.-k PACS numbers:
With the rapid development of information and communication technology, data empowerment has become an important way for platform service supply chain (PSSC) members to obtain a competitive advantage. Based on the three-level PSSC network structure composed of service providers, platform operators, and demand markets, this paper assumes that platform operators empower service providers to improve service quality, and PSSC members invest in data security risk control. Then, using variational inequality and equilibrium theory, a supply chain network equilibrium model considering data empowerment is constructed, and the equilibrium conditions of the whole network are obtained. Based on numerical examples, this paper analyzes the impact of the sensitivity of the demand market to service quality, the relative importance of service providers’ service quality improvement level, the data empowerment cost of PSSC members, and the data security risk control investment of PSSC members on the equilibrium state of the supply chain network. The results show the following: because the service quality is produced by the cooperation between service providers and platform operators, platform operators may have free-riding behavior and are only willing to invest a fixed data empowerment cost to ensure the essential service quality; data security risk control investment is an important factor affecting service sales; and when supply chain network members reduce data security risk control investment, consumers’ willingness to pay for services will be reduced, resulting in a decline in the overall profit of the supply chain network.
We investigate the cosmological evolution of the power law k-essence dark energy (DE) model with interaction in FRWL spacetime with the Lagrangian that contains a kinetic function F(X)=−X+X. Concretely, the cosmological evolution in this model are discussed by the autonomous dynamical system and its critical points, together with the corresponding cosmological quantities, such as Ωϕ, wϕ, cs2, and q, are calculated at each critical point. The evolutionary trajectories are drawn in order to show the dynamical process on the phases plan around the critical points. The result that we obtained indicates that there are four dynamical attractors, and all of them correspond to an accelerating expansion of universe for certain potential parameter and coupling parameter. Besides that, the geometrical diagnostic by the statefinder hierarchy S3(1) and S4(1) of this scalar field model are numerically obtained by the phase components, as an extended null diagnostic for the cosmological constant. This diagnostic shows that both the potential parameter λ and interaction parameter α play important roles in the evolution of the statefinder hierarchy.
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