分类: 物理学 提交时间: 2016-05-08
摘要: Based on the universal properties of a critical point in different systems and that the QCD phase transitions fall into the same universality classes as the 3-dimensional Ising, O(2) or O(4) spin models, the critical behavior of cumulants and higher cumulant ratios of the order parameter from the three kinds of spin models is studied. We found that all higher cumulant ratios change dramatically the sign near the critical temperature. The qualitative critical behavior of the same order cumulant ratio is consistent in these three models.
分类: 物理学 提交时间: 2016-05-08
摘要: Binder liked ratios of baryon number are firstly suggested in relativistic heavy ion collisions. Using 3D-Ising model, the critical behavior of Binder ratios and ratios of higher order cumulants of order parameter are fully presented. Binder ratio is shown to be a step function of temperature. The critical point is the intersection of the ratios of different system sizes between two platforms. From low to high temperature through the critical point, the ratios of third order cumulants change their values from negative to positive in a valley shape, and ratios of fourth order cumulants oscillate around zero. The normalized ratios, like the Skewness and Kurtosis, do not diverge with correlation length, in contrary with corresponding cumulants. Applications of these characters in search critical point in relativistic heavy ion collisions are discussed.
分类: 物理学 提交时间: 2016-05-08
摘要: QCD deconfinement phase transition is supposed to be the same universality class as the 3D-Ising model. According to the universality of critical behavior, the Binder-like ratios and ratios of higher cumulants of order parameter near the critical temperature in the 3D-Ising model are studied. The Binder-like ratio is shown to be a step function of temperature. The critical point is the intersection of the ratios of different system sizes between two platforms. The normalized cumulant ratios, like the Skewness and Kurtosis, do not diverge with correlation length, contrary to the corresponding cumulants. Possible applications of these characters in locating critical point in relativistic heavy ion collisions are discussed.
分类: 物理学 提交时间: 2016-05-08
摘要: By considering the fluctuation of grand potential Omega around equilibrium with respect to small one-particle density fluctuations delta rho(alpha)((gamma) over right arrow), the phase instability of restricted primitive model (RPM) of ionic systems is investigated. We use the integral equation theory to calculate the direct correlation functions in the reference hypernetted chain approximation and obtain the spinodal line of RPM. Our analysis explicitly indicates that the gas-fluid phase instability is induced by k = 0 fluctuation mode, while the fluid-solid phase instability is related to k not equal 0 fluctuation modes. The spinodal line is qualitatively consistent with the result or computer simulations by others.
分类: 物理学 提交时间: 2016-05-08
摘要: Using the reference hypernetted chain (RHNC) integral equation theory and a rigorous stability analysis method, we investigate the phase behavior of a mixture of hard-sphere dipoles and neutral hard spheres based on the correlations of the homogeneous isotropic phase. Lowering the temperature down to the points where the RHNC equations fail to have a solution, several fluctuations strongly increase. At low densities our results indicate the onset of chain formation, which is similar with the pure DHS system. At high densities, the results indicate the appearance of isotropic-to-ferroelectric transitions (small neutral hard spheres concentrations) and demixing transitions (large neutral hard spheres concentrations).
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: Self-questioning mechanism which is similar to single spin-flip of Ising model in statistical physics is introduced into spatial evolutionary game model. We propose a game model with altruistic to spiteful preferences via weighted sums of own and opponent’s payoffs. This game model can be transformed into Ising model with an external field. Both interaction between spins and the external field are determined by the elements of payoff matrix and the preference parameter. In the case of perfect rationality at zero social temperature , this game model has three different phases which are entirely cooperative phase, entirely non-cooperative phase and mixed phase. In the investigations of the game model with Monte Carlo simulation, two paths of payoff and preference parameters are taken. In one path, the system undergos a discontinuous transition from cooperative phase to non-cooperative phase with the change of preference parameter. In another path, two continuous transitions appear one after another when system changes from cooperative phase to non-cooperative phase with the prefenrence parameter. The critical exponents and of two continuous phase transitions are estimated by the finite-size scaling analysis. Both continuous phase transitions have the same critical exponents and they belong to the same universality class as the two-dimensional Ising model.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: We calculate the Casimir force at a finite cut-off Lambda by summing the forces induced by the all fluctuation modes. We show that the Casimir force is independent of the cut-off function in the limit L Lambda -> infinity. There is a correction in the order of (L Lambda)(-2), when L Lambda is finite and large. This correction becomes remarkable when L is comparable with the microscopic length scale Lambda(-1). It has been demonstrated that the Casimir force at a finite cut-off should be defined by summing forces of all fluctuation modes, instead of the derivative of Casimir energy with respect to L where an additional derivative of the cut-off function has been introduced.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: The phase transition of Heisenberg fluid has been investigated with the density functional theory in mean-field approximation (MF). The matrix of the second derivatives of the grand canonical potential Omega with respect to the particle density fluctuations and the magnetization fluctuations has been investigated and diagonalized. The smallest eigenvalue being 0 signalizes the phase instability and the related eigenvector characterizes this phase transition. We find a Curie line where the order parameter is pure magnetization and a spinodal where the order parameter is a mixture of particle density and magnetization. Along the spinodal, the character of phase in stability changes continuously from predominant condensation to predominant ferromagnetic phase transition with the decrease of total density. The spinodal meets the Curie line at the critical end point with the reduced density rho* = rho sigma(3) = 0.224 and the reduced temperature T* = kT/epsilon = 1.87 (sigma is the diameter of Heisenberg hard sphere and epsilon is the coupling constant).
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: Aiming to understand real-world hierarchical networks whose degree distributions are neither power law nor exponential, we construct a hybrid clique network that includes both homogeneous and inhomogeneous parts, and introduce an inhomogeneity parameter to tune the ratio between the homogeneous part and the inhomogeneous one. We perform Monte-Carlo simulations to study various properties of such a network, including the degree distribution, the average shortest-path-length, the clustering coefficient, the clustering spectrum, and the communicability.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: We design an irreversible Markov chain Monte Carlo algorithm for the self-avoiding walk (SAW). It outperforms the Berretti-Sokal algorithm. The gained efficiency increases with the spatial dimension, from about 10 times in two dimensions to around 40 times in five dimensions. The algorithm violates the widely used detailed balance condition and satisfies the weaker balance condition. We employ the irreversible method to study the finite-size scaling of SAW above the upper critical dimension.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: The gravitational collapse of a massless scalar field with a self-interaction term lambda phi(4) in anti-de Sitter space is investigated. We numerically investigate the effect of the self-interaction term on the critical amplitudes, forming time of apparent horizon, stable island, and energy transformation. The results show that a positive A suppresses the formation of black hole, while a negative A enhances the process. We define two susceptibilities to characterize the effect of the self-interaction on the black hole formation, and find that near the critical amplitude, there exists a universal scaling relation with the critical exponent alpha approximate to 0.74 for the time of black hole formation.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: Within massive gravity, we construct a gravity dual for the insulator/metal phase transition and colossal magnetoresistance effect found in some manganese oxides materials. In the heavy graviton limit, a remarkable magnetic-field-sensitive DC resistivity peak appears at the Curie temperature, where an insulator/metal phase transition happens and the magnetoresistance is scaled with the square of field-induced magnetization. We find that metallic and insulating phases coexist below the Curie point and the relation with the electronic phase separation is discussed.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: In this paper we investigate in some detail the holographic ferromagnetic phase transition in an AdS(4) black brane background by introducing a massive 2-form field coupled to the Maxwell field strength in the bulk. In two probe limits, one is to neglect the back reaction of the 2-form field to the background geometry and to the Maxwell field, and the other to neglect the back reaction of both the Maxwell field and the 2-form field, we find that the spontaneous magnetization and the ferromagnetic phase transition always happen when the temperature gets low enough with similar critical behavior. We calculate the DC resistivity in a semi-analytical method in the second probe limit and find it behaves as the colossal magnetic resistance effect in some materials. In the case with the first probe limit, we obtain the off-shell free energy of the holographic model near the critical temperature and compare with the Ising-like model. We also study the back reaction effect and find that the phase transition is always second order. In addition, we find an analytical Reissner-Norstrom-like black brane solution in the Einstein-Maxwell-2-form field theory with a negative cosmological constant.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: A holographic description on the antiferromagnetic quantum phase transition (QPT) induced by the magnetic field and the criticality in the vicinity of the quantum critical point have been investigated numerically recently. In this paper, we show that the properties of QPT in this holographic model are governed by a CFT dual to the emergent AdS(2) in the IR region, which confirms that the dual boundary theory is a strong coupling theory with dynamic exponent z = 2 and logarithmic corrections appearing. We also compare them with the results from the Hertz model by solving the RG equation at its upper critical dimension and with some experimental data from pyrochlores Er2-2xY2xTi2O7 and BiCoPO5.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: A real antisymmetric tensor field was introduced to realize a holographic magnetic ordered phase in our previous papers. However, a more careful analysis shows there is a vector ghost in the model. In this paper we present a modified Lagrangian density for the antisymmetric tensor, which is ghost free and causality is well defined, and keeps all the significant results in the original model qualitatively. We show this modified Lagrangian density could come from the dimensional compactification of p-form field in string/M theory. For static curved space-time, we also prove that this modified model is ghost free and does not violate causality. This new model offers a solid foundation for the application of antisymmetric tensor field in holographic duality, especially for the spontaneous magnetization.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: In the last years it has been shown that some properties of strongly coupled superconductors can be potentially described by classical general relativity living in one higher dimension, which is known as holographic superconductors. This paper gives a quick and introductory overview of some holographic superconductor models with s-wave, p-wave and d-wave orders in the literature from point of view of bottom-up, and summarizes some basic properties of these holographic models in various regimes. The competition and coexistence of these superconductivity orders are also studied in these superconductor models.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: We propose a gravity dual of antiferromagnetic quantum phase transition induced by magnetic field and study the critical behavior around the quantum critical point. It turns out that the boundary critical theory is a strong coupling theory with dynamic exponent z = 2 and that the hyperscaling law is violated and logarithmic corrections appear near the quantum critical point. Some novel scaling relations are predicated, which can be tested by experiment data in the future. We also make some comparison with experimental data on low-dimensional magnets BiCoPO5 and pyrochlores Er2-2xY2xTi2O7.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: 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.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: 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 an external magnetic field and in low temperatures, the magnetic moments condense spontaneously in an antiparallel manner with the same magnitude and the time reversal symmetry is also broken spontaneously (if the 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 the 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 the antiferromagnetic phase: when the magnetic field reaches Bc, the system will return into the paramagnetic phase by a second order phase transition.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: 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.