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.
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.
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.
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.
118431152
Dynamics of generalized tachyon field
We investigate the dynamics of generalized tachyon field in FRW spacetime. We obtain the autonomous dynamical system for the general case. Because the general autonomous dynamical system cannot be solved analytically, we discuss two cases in detail: β=1 and β=2. We find the critical points and study their stability. At these critical points, we also consider the stability of the generalized tachyon field, which is as important as the stability of critical points. The possible final states of the universe are discussed.
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.
119237909
Modified clock inequalities and modified black hole lifetime
Based on a generalized uncertainty principle, Salecker-Wigner inequalities are modified. When applied to black holes, they give a modified black hole lifetime: T-MB similar to M-3/m(p)(3)(1 - m(p)(2)/M-2)t(p), and the number of bits required to specify the information content of the black hole as the event horizon area in Planck units N similar to M-2/m(p)(2)(1 - m(p)(2)/M-2).
118610087
Asymptotically safe phantom cosmology
We consider quantum modifications to phantom cosmology in a Friedmann–Robertson–Walker spacetime. The cosmological evolution equations improved by the renormalization group are obtained. For exponential potential, we find two types of cosmological fixed point; the renormalization group scale either freezes in, or continues to evolve with scale factor. We discuss the implications of each of these points, and investigate especially whether the big rip can be avoided. If the fixed point of renormalization group flow coincides with the cosmological fixed point, the universe will be dominated by dark matter and will be free from the big rip.
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.