分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We investigate the implications of the entropic force formalism proposed by Verlinde. We show that an UV/IR relation proposed by Cohen et al., as well as an uncertainty principle proposed by Hogan can be derived from the entropic force formalism. We show that applying the entropic force formalism to cosmology, there is an additional term in the Friedmann equation, which can be identified as holographic dark energy. We also propose an intuitive picture of holographic screen, which can be thought of as an improvement of Susskind's holographic screen.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We compute the Casimir energy of the photon field in a static de Sitter space and find it to be proportional to the size of the horizon, the same form of the holographic dark energy. We suggest to make metamaterials to mimic static de Sitter space in laboratory and measure the predicted Casimir energy. Crown
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We applied the transformation optics to mimic a black hole of Schwarzschild form. Similar properties of photon sphere were also found numerically for the metamaterial black hole. Several reduced versions of the black hole systems were proposed for easier implementations.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We investigate the cosmic age problem associated with 9 extremely old globular clusters in M31 galaxy and 1 very old high-z quasar automatic plate-measuring machine 08279 + 5255 at z = 3.91. These 9 globular clusters have not been used to study the cosmic age problem in the previous literature. By evaluating the age of the Universe in the Lambda cold dark matter model with the observational constraints from the Type Ia supernovae, the baryon acoustic oscillations, the cosmic microwave background, and the independent H-0 measurements, we find that the existence of 5 globular clusters and 1 high-z quasar are in tension (over 2 sigma confidence level) with the current cosmological observations. So if the age estimates of these objects are correct, the cosmic age puzzle still remains in the standard cosmology. Moreover, we extend our investigations to the cases of the interacting dark energy models. It is found that although the introduction of the interaction between dark sectors can give a larger cosmic age, the interacting dark energy models still have difficulty to pass the cosmic age test.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We propose a scheme to mimic the expanding cosmos in 1 2 dimensions in laboratory. Furthermore, we develop a general procedure to use nonlinear metamaterials to mimic D-brane and noncommutativity in string theory.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We investigate the Hamiltonian formulation of f(T) gravity and find that there are five degrees of freedom. The six first class constraints corresponding to the local Lorentz transformation in Teleparallel gravity become second class constraints in f(T) gravity, which leads to the appearance of three extra degrees offreedom and the violation of the local Lorentz invariance in f(T) gravity. In general, there are D-1 extra degrees of freedom for f(T) gravity in D dimensions, and this implies that the extra degrees of freedom correspond to one massive vector field or one massless vector field with one scalar field.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We prove that, in general the first law of black hole thermodynamnics, delta Q = T delta S, is violated in f(T) gravity. As a result, it is possible that there exists entropy production, which implies that the black hole thermodynamics can be in non-equilibrium even in the static spacetime. This feature is very different from that of f(R) or that of other higher derivative gravity theories. We find that the violation of first law results from the lack of local Lorentz invariance in f(T) gravity. By investigating two examples, we note that f ''(0) should be negative in order to avoid the naked singularities and superluminal motion of light. When f ''(T) is small, the entropy of black holes in f(T) gravity is approximatively equal to (f'(T))/(4)A
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: The possibility of reconstructing a spherically symmetric inhomogeneous Lemaitre-Tolman-Bondi (LTB) model with Lambda CDM observations has drawn much attention. Recently, an inhomogeneous LTB model having the same luminosity-distance and light-cone mass density of the homogeneous Lambda CDM model was reconstructed. From the Wilkinson microwave anisotropy probe 7-year measurements together with other cosmological observations, we calculate the cosmic age at our position in this LTB model, and obtain a constraint t(LTB) < 11.7 Gyr at 1 sigma confidence level. We find that this result is, although 2 Gyr younger compared with the age of the homogeneous Lambda CDM model, still within 1 sigma agreement with the constraint of cosmic age given by current astronomical measurements. We expect that in the future, with the help of more advanced observations, we can distinguish the reconstructed inhomogeneous LTB model from the homogeneous Lambda CDM model.