119246119
Constraints on the generalized tachyon field models from latest observational data
We consider constraints on generalized tachyon field (GTF) models from latest observational data (including 182 gold SNIa data, the shift parameter, and the acoustic scale). We obtain at 68.3% confidence level Ωm = 0.37 ± 0.01, k0 = 0.09−0.03+0.04, α = 1.8−0.7+7.4 (the best fit values of the parameters) and zq = 0~0.47−0.51 (the transitional redshift) for GTF as the dark energy component only; k0 = 0.21−0.18+0.20, α = 0.57 ± 0.01 and zq = 0~0.49–0.68 for GTF as the unification of dark energy and dark matter. In both cases, GTF evolves like dark matter in the early universe. By applying model-comparison statistics and testing with independent H(z) data, we find that the GTF dark energy scenario is favored over the ΛCDM model, and the ΛCDM model is favored over GTF unified dark matter by the combined data. For GTF as the dark energy component, the fluctuations of matter density are consistent with the growth of linear density perturbations. For GTF unified dark matter, the growth of GTF density fluctuations goes more slowly for , meaning that GTF does not behave as classical ΛCDM scenarios.
118714602
SPATIAL RICCI SCALAR DARK ENERGY MODEL
Inspired by the holographic principle, we suggest that the density of dark energy is proportional to the spatial Ricci scalar curvature (SRDE). Such a model is phenomenologically viable. The best fit values of its parameters at 68% confidence level are found to be Ωm 0 = 0.259±0.016 and α = 0.261±0.0122, constrained from the Union+CFA3 sample of 397 SNIa and the BAO measurement. We find that the equation of state of SRDE crosses -1 at z ≃ -0.14. The present value of the deceleration parameter q(z) for SRDE is found to be qz = 0~-0.85. The phase transition from deceleration to acceleration of the Universe for SRDE occurs at the redshift zq = 0~0.4. After studying the perturbation of each component of the Universe, we show that the matter power spectra and cosmic microwave background temperature anisotropy are slightly affected by SRDE, compared with ΛCDM.
119246835
Conformal transformation in f(T) theories
It is well known that f(R) theories are dynamically equivalent to a particular class of scalar-tensor theories. In analogy to the f(R) extension of the Einstein-Hilbert action of general relativity, f(T) theories are generalizations of the action of teleparallel gravity. The field equations are always second order, remarkably simpler than f(R) theories. It is interesting to investigate whether f(T) theories have the similar conformal features possessed in f(R) theories. It is shown, however, that f(T) theories are not dynamically equivalent to teleparallel action plus a scalar field via conformal transformation, since there appears an additional scalar-torsion coupling term. We discuss briefly what constraint of this coupling term may be put on f(T) theories from observations of the solar system.
119105820
Geometrical diagnostic for purely kinetic k-essence dark energy
Abstract Geometrical diagnostic, involving the statefinder { r , s } and Om ( x ) , is widely used to discriminate different dark energy models. We apply the statefinder { r , s } and Om ( x ) to purely kinetic k-essence dark energy model with Dirac–Born–Infeld-like Lagrangian which can be considered as scalar field realizations of Chaplygin gas. We plot the evolution trajectories of this model in the statefinder parameter-planes and Om ( x ) parameter-plane. We find that the statefinder { r , s } and Om ( x ) fail to distinguish purely kinetic k-essence model from ΛCDM model at 68.3% confidence level for z ≪ 1 .
118724058
The evolution of the power law k-essence cosmology
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 Ωϕ and wϕ, 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.
120945447
Observational Constraints on Purely Kinetic k -Essence Dark Energy Models
We consider constraints on purely kinetic k-essence models from the latest observational data (including 182 gold SNIa data, the shift parameter, and the acoustic scale). We find the best-fit values of the parameters are Ωm = 0.37 ± 0.01 and k0 = 0.064 ± 0.013 at 68.3% confidence level. The phase transition from deceleration to acceleration is found to occur at redshift zq = 0 ~ 0.48−0.52 in 68.3% confidence level limits. By applying model-comparison statistics (F-test, AICc, and BIC), we find that the purely kinetic k-essence scenario is favored over the ?CDM model by the combined data. These results are also confirmed by combined data 307 SNIa + R + la.
119262542
Coexistence and competition of ferromagnetism and p-wave superconductivity in holographic model
By combining a holographic $p$-wave superconductor model and a holographic ferromagnetism model, we study the coexistence and competition of ferromagnetism and $p$-wave superconductivity. It is found that the results depend on the self-interaction of magnetic moment of the complex vector field and which phase appears first. In the case where the ferromagnetic phase appears first, if the interaction is attractive, the system shows the ferromagnetism and superconductivity can coexist at low temperatures. If the interaction is repulsive, the system will only be in a pure ferromagnetic state. In the case where the superconducting phase appears first, the attractive interaction will lead to a magnetic $p$-wave superconducting phase at low temperatures. If the interaction is repulsive, the system will be in a pure $p$-wave superconducting phase or a ferromagnetic phase when the temperature is lowered.
119108999
Holographic model for the paramagnetism/antiferromagnetism phase transition
In this paper we build a holographic model of paramagnetism/antiferromagnetism phase transition, which is realized by introducing two real antisymmetric tensor fields coupling to the background gauge field strength and interacting with each other in a dyonic black brane background. In the case without external magnetic field and in low temperatures, the magnetic moments condense spontaneously in antiparallel manner with the same magnitude and the time reversal symmetry is also broken spontaneously (if boundary spatial dimension is more than 2, spatial rotational symmetry is broken spontaneously as well), which leads to an antiferromagnetic phase. In the case with weak external magnetic field, the magnetic susceptibility density has a peak at the critical temperature and satisfies the Curie-Weiss law in the paramagnetic phase of antiferromagnetism. In the strong external magnetic field case, there is a critical magnetic field $B_c$ in antiferromagnetic phase: when magnetic field reaches $B_c$, the system will return into the paramagnetic phase by a second order phase transition.
119285015
P-V criticality in the extended phase space of Gauss-Bonnet black holes in AdS space
A bstractWe study the P − V criticality and phase transition in the extended phase space of charged Gauss-Bonnet black holes in anti-de Sitter space, where the cosmological constant appears as a dynamical pressure of the system and its conjugate quantity is the thermodynamic volume of the black holes. The black holes can have a Ricci flat (k = 0), spherical (k = 1), or hyperbolic (k = −1) horizon. We find that for the Ricci flat and hyperbolic Gauss-Bonnet black holes, no P − V criticality and phase transition appear, while for the black holes with a spherical horizon, even when the charge of the black hole is absent, the P − V criticality and the small black hole/large black hole phase transition will appear, but it happens only in d = 5 dimensions; when the charge does not vanish, the P − V criticality and the small black hole/large phase transition always appear in d = 5 dimensions; in the case of d ≥ 6, to have the P − V criticality and the small black hole/large black hole phase transition, there exists an upper bound for the parameter $ b=\widetilde{\alpha }{{\left| Q \right|}^{{{-2 \left/ {{\left( {d-3} \right)}} \right.}}}} $, where $ \widetilde{\alpha } $ is the Gauss-Bonnet coefficient and Q is the charge of the black hole. We calculate the critical exponents at the critical point and find that for all cases, they are the same as those in the van der Waals liquid-gas system.