分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We demonstrate the attractor behavior of inflation driven by a scalar field or a tachyon field in the context of recently proposed four-dimensional effective gravity induced on the world-volume of a three-brane in five-dimensional Einstein gravity, and we obtain a set of exact inflationary solutions.Phase portraits indicate that an initial kinetic term decays rapidly and it does not prevent the onset of inflation. The trajectories more rapidly reach the slow rolling curve in braneworld scenario than in the standard cosmology.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: The w−w′ plane, defined by the equation of state parameter for the dark energy and its derivative with respect to the logarithm of the scale factor, is useful to the study of classifying the dynamical dark energy models. In this note, we examine the evolving behavior of the two-field quintom models with w crossing the w = −1 barrier in the w − w′ plane. We find that these models can be divided into two categories, type A quintom in which w changes from > −1 to −1 as the universe expands.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: Although there is mounting observational evidence that the expansion of our universe is undergoing a late-time acceleration, the mechanism for this acceleration is yet unknown. In the so-called Dvali-Gabadadze-Porrati (DGP) model this phenomena is attributed to gravitational leakage into extra dimensions. In this work, we mainly focus our attention to the constraints on the model from the gold sample of type Ia supernovae (SNeIa), the first year data from the Supernova Legacy Survey (SNLS) and the baryon acoustic oscillation (BAO) peak found in the Sloan Digital Sky Survey (SDSS). At 99.73% confidence level, the combination of the three databases provides m = 0.270+0.018−0.017 and rc = 0.216+0.012−0.013 (hence a spatially closed universe with k = −0.350+0.080−0.083), which seems to be in contradiction with the most recent WMAP results indicating a flat universe. Based on this result, we also estimated the transition redshift (at which the universe switches from deceleration to acceleration) to be 0.70 < zq=0 < 1.01, at 2#27;confidence level.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We construct the non-canonical kinetic term of a k-essence field directly from the effective equation of state function wk(z), which describes the properties of the dark energy.Adopting the usual parametrizations of equation of state we numerically reproduce the shape of the non-canonical kinetic term and discuss some features of the constructed form of k-essence.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We investigate observational constraints on the variable Chaplygin gas model from the gold sample of type Ia supernova data and the recent measurements of the X-ray gas mass fractions in galaxy clusters. Combining these databases, we obtain a tight constraint on the two model parameters. Our results indicate that the original Chaplygin gas model is ruled out by the data at 99.7% confidence level.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We consider a new generalized Chaplygin gas model that includes the original Chaplygin gas model as a special case. In such a model the generalized Chaplygin gas evolves as from dust to quiessence or phantom. We show that the background evolution for the model is equivalent to that for a coupled dark energy model with dark matter. The constraints from the current type Ia supernova data favour a phantom-like Chaplygin gas model.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We develop a theoretical method of constructing the quintessence potential directly from the effective equation of state function w(z), which describes the properties of the dark energy. We apply our method to four parametrizations of equation of state parameter and discuss the general features of the resulting potentials. In particular, it is shown that the constructed quintessence potentials are all in the form of a runaway type.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We investigate the cosmological evolution of an interacting phantom energy model in which the phantom field has interaction with the dark matter. We discuss the existence and stability of scaling solutions for two types of specific interactions. One is motivated by the conformal transformation in string theory and the other is motivated by analogy with dissipation. In the former case, there exist no scaling solutions. In the latter case, there exist stable scaling solutions, which may give a phenomenological solution of the coincidence problem. Furthermore, the universe either accelerates forever or ends with a singularity, which is determined by not only the model parameters but also the initial velocity of the phantom field.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We investigate the role of a suitable interaction between a matter fluid and a phantom field for the coincidence problem. There exists a stationary scaling solution which is a stable attractor at late times. Furthermore, the cosmic doomsday is avoided in one region of the parameter space
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We investigate in this paper the cosmological evolution of a dark energy model with two scalar fields where one of the scalar has canonical kinetic energy and another scalar has negative kinetic energy term. For such a system with exponential potentials we find that during the evolution of the universe the equation of state w changes from w > −1 to w < −1, which is consistent with the recent observations. A phase-plane analysis shows that the “phantom”-dominated scaling solution is the stable late-time attractor of this type of models.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We investigate the cosmological attractor of the minimally coupled, self-interacting phantom field with a positive energy density but negative pressure. It is proved that the phantom cosmology is rigid in the sense that there exists a unique attractor solution. We plot the trajectories in the phase space numerically for the phantom field with three typical potentials. Phase portraits indicate that an initial kinetic term decays rapidly and the trajectories reach the unique attractor curve. We find that the curve corresponds to the slow-climb solution.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We investigate cosmological dynamics of multiple tachyon fields with inverse square potentials.A phase-space analysis of the spatially flat FRW models shows that there exists power-law cosmological scaling solutions. We study the stability of the solutions and find that the potential-kinetic-scaling solution is a global attractor. However, in the presence of a barotropic fluid the solution is an attractor only in one region of the parameter space and the tracking solution is an attractor in the other region. We briefly discuss the physical consequences of these results.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We present a phase-space analysis of cosmology containing multiple scalar fields with positive and negative exponential potentials. We show that there exist power-law multi-kinetic potential scaling solutions for sufficiently flat positive potentials or steep negative potentials.The former is the unique late-time attractor and the well-known assisted inflationary solution, but the later is never unstable in an expanding universe. Moreover, for steep negative potentials there exist a kinetic-dominated regime in which each solution is a late-time attractor. We briefly discuss the physical consequences of these results.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-17
摘要: We analyze various possible interpretations of the narrow state D+sJ (2632) observed by SELEX Collaboration recently, which lies above threshold and has abnormal decay pattern. These interpretations include: (1) several versions of tetraquarks; (2) conventional cs¯ meson such as the first radial excitation of Ds(2112) with abnormally large SU(3) symmetry breaking; (3) conventional cs¯ meson with abnormally large η1 coupling; (4) heavy hybrid meson. We discuss the physical implications of each interpretation. For example, if the existence of D +sJ (2632) is confirmed as the first radial excitation of Ds(2112) by other experiments, it will be helpful to look for (1) its SU(3) flavor partners D 0,+J(2530); (2) its B-meson analogues B0,+J(5840), B+sJ (5940); (3) S-wave two pion decaymodes.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-17
摘要: In the framework of heavy quark effective theory we use QCD sum rules to calculate the masses of the ¯cs (0+, 1+) and (1+, 2+) excited states. The results are consistent with that the states DsJ (2317) and DsJ (2460) observed by BABAR and CLEO are the 0+ and 1+ states in the jl =12+doublet.