120520435
Bound on the Equation of State of Dark Energy from the Generalized Second Law of Thermodynamics
Assuming that the equation of state of dark energy is a constant, we obtain the allowed interval of the equation of state of dark energy: wD≥−1, bounded from the generalized second law of thermodynamics, in a universe enveloped by the apparent horizon and containing a Schwarzschild black hole.
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.
119037938
New types of f(T) gravity
Recently f(T) theories based on modifications of teleparallel gravity, where torsion is the geometric object describing gravity instead of curvature, have been proposed to explain the present cosmic accelerating expansion. The field equations are always second order, remarkably simpler than f(R) theories. In analogy to the f(R) theory, we consider here three types of f(T) gravity, and find that all of them can give rise to cosmic acceleration with interesting features, respectively.
121495245
Theoretical Constraint on Purely Kinetic k -Essence
Purely kinetic k-essence models in which the Lagrangian contains only a kinetic factor and does not depend explicitly on the field itself are considered, and a theoretical constraint is obtained: Fx = F0a−3. Under this theoretical constraint, we discuss a kind of purely k-essence with form F(X) = -(1 + 2Xn)1/2n, which can be considered as the generalized tachyon field, and find that this kind of k-essence is not likely a candidate of dark energy to describe the present accelerated expansion of the Universe. This is contrary to a previous suggestion that k-essence with such a form may be used to describe phantom cosmologies.
119289134
Large-scale structure in superfluid Chaplygin gas cosmology
We investigate the growth of the large-scale structure in the superfluid Chaplygin gas (SCG) model. Both linear and nonlinear growth, such as sigma(8) and the skewness S-3, are discussed. We find the growth factor of SCG reduces to the Einstein-de Sitter case at early times while it differs from the cosmological constant model (ACDM) case in the large a limit. We also find there will be more stricture growth on large scales in the SCG scenario than in ACDM and the variations of sigma 8 and S-3 between SCG and ACDM cannot be discriminated.
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.
12639048
Towards complete phase diagrams of a holographic p-wave superconductor model
A bstractWe study in detail the phase structure of a holographic p-wave superconductor model in a five dimensional Einstein-Maxwell-complex vector field theory with a negative cosmological constant. To construct complete phase diagrams of the model, we consider both the soliton and black hole backgrounds. In both two cases, there exist second order, first order and zeroth order phase transitions, and the so-called “retrograde condensation” also happens. In particular, in the soliton case with the mass of the vector field being beyond a certain critical value, we find a series of phase transitions happen such as “insulator/superconductor/insulator/superconductor”, as the chemical potential continuously increases. We construct complete phase diagrams in terms of temperature and chemical potential and find some new phase boundaries.
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.
118361149
Paramagnetism-ferromagnetism phase transition in a dyonic black hole
Coupling an antisymmetric tensor field to the electromagnetic field in a dyonic Reissner-Nordstrom-anti-de Sitter black hole background, we build a holographic model for the paramagnetism/ferromagnetism phase transition. In the case of zero magnetic field, the time reversal symmetry is broken spontaneously and spontaneous magnetization happens at low temperatures. The critical exponents are in agreement with the ones from mean field theory. In the case of nonzero magnetic field, the model realizes the hysteresis loop of a single magnetic domain and the magnetic susceptibility satisfies the Curie-Weiss law.