Growth of linear matter perturbations and current observational constraints

We discuss, using a recently proposed parametrization for the growth index of linear matter perturbations, the observational constraints on the wCDM model and the Dvali—Gabadadze—Porrati (DGP) model with all current growth factor data. We find that the wCDM model is allowed by the observations at the 1$\sigma$ confidence level, while the DGP model is only consistent with observations at 2$\sigma$ confidence level.     

The damping rate of plasma waves in condensed matter

It is the purpose of this paper to give an analytical expression for the damping rate of a long-wavelength plasma wave in terms of the optical constants of the medium which supports the wave. This expression is a generalization of that given in the literature for a free electron gas. The expression is derived by two different methods below.     

The growth factor of matter perturbations in f(R) gravity

The growth of matter perturbations in the f(R) model proposed by Starobinsky is studied in this paper. Three different parametric forms of the growth index are considered respectively, and constraints on the model are obtained at both the 1σ and 2σ confidence levels, by using the current observational data for the growth factor. It is found, for all the three parametric forms of the growth index examined, that the Starobinsky model is consistent with the observations only at the 2σ confidence level.     

Phantom dark energy with varying-mass dark matter particles: Acceleration and cosmic coincidence problem

We investigate several varying-mass dark matter particle models in the framework of phantom cosmology. We examine whether there exist late-time cosmological solutions, corresponding to an accelerating universe and possessing dark energy and dark matter densities of the same order. Imposing exponential or power-law potentials and exponential or power-law mass dependence, we conclude that the coincidence problem cannot be solved or even alleviated. Thus, if dark energy is attributed to the phantom paradigm, varying-mass dark matter models cannot fulfill the basic requirement that led to their construction.     

Adiabatic density perturbations and matter generation from the minimal supersymmetric standard model

We propose that the inflaton is coupled to ordinary matter only gravitationally and that it decays into a completely hidden sector. In this scenario both baryonic and dark matter originate from the decay of a flat direction of the minimal supersymmetric standard model, which is shown to generate the desired adiabatic perturbation spectrum via the curvaton mechanism. The requirement that the energy density along the flat direction dominates over the inflaton decay products fixes the flat direction almost uniquely. The present residual energy density in the hidden sector is typically shown to be small.     

On the growth of perturbations in interacting dark energy and dark matter fluids

The covariant generalizations of the background dark sector coupling suggested in Mangano, Miele and Pettorino (Mod Phys Lett A 18:831, 2003) are considered. The evolution of perturbations is studied with detailed attention to interaction rate that is proportional to the product of dark matter and dark energy densities. It is shown that some classes of models with coupling of this type do not suffer from early time instabilities in strong coupling regime.     

The effect of random matter density perturbations on the MSW solution to the solar neutrino problem

We consider the implications of solar matter density random noise upon resonant neutrino conversion. The evolution equation describing MSW-like conversion is derived in the framework of the Schrödinger approach. We study quantitatively the effect of such matter perturbations upon both large and small mixing angle MSW solutions to the solar neutrino problem. This is carried out both for the active-active v_e → v_μ,τ as well as active-sterile v_e → v_s conversion channels. We find that the small mixing MSW solution is much more stable (especially in Δm² than the large mixing solution. The possible existence of solar matter density noise at the few percent level could be tested at future solar neutrino experiments, especially Borexino.     

Euclidean Wormholes with Phantom Field and Phantom Field Accompanied by Perfect Fluid

We study the classical Euclidean wormhole solutions for the gravitational systems with minimally coupled pure Phantom field and minimally coupled Phantom field accompanied by perfect fluid. It is shown that such solutions do exist and then the general forms of the Phantom field potential are obtained for which there are classical Euclidean wormhole solutions.     

Discontinuous perturbations

Perturbations of quantum systems ranging from oscillators to fields can be either continuous or discontinuous functions of the coupling. The system under consideration is the familiar harmonic oscillator in one degree of freedom. Previous studies have shown that when the harmonic oscillator is subjected to a perturbation with a power law singularity, a permanent change in the system characteristics is observed for a specific range of power law values. The introduction of a logarithmic singularity into the power law potential fine tunes the singularity power.     

Phantom inflation in little rip

We study the phantom inflation in little rip cosmology, in which the current acceleration is driven by the field with the parameter of state w<−1$w<-1$, but since w tends to −1 asymptotically, the rip singularity occurs only at infinite time. In this scenario, before the rip singularity is arrived, the universe is in an inflationary regime. We numerically calculate the spectrum of primordial perturbation generated during this period and find that the results may be consistent with observations. This implies that if the reheating happens again, the current acceleration might be just a start of phantom inflation responsible for the upcoming observational universe.     

Gentle perturbations

By introducing a specific type of perturbation,A, in the Hamiltonian, we define a class of gently perturbed states, ,A, of a canonical ensemble, . The perturbations are chosen so as to preserve a relationship of the form ,A constant ×. Applications in ergodic theory and phase transitions are described.     

Overlooked perturbations

An important class of overlooked mhd perturbations is reported. For incompressible fluids the class consists of perturbations which cannot be written as gradients.     

K-Essential Phantom Energy: Revisited

We generalize some of those results which are closely related to the canonical kinetic term in k-essence formalism by further tuning the parameter (β). The scale factor a(t) could be negative and decreasing within a specific range of β (≡−1/ω, ω : the equation-of-state parameter) during the initial evolutional period.     

利用阻尼振动测量气垫导轨阻尼系数的新思路

利用气垫导轨上两根弹簧连接滑块做阻尼振动的模型,通过求解阻尼振动方程推算得到了滑块运动的最大速度衰减式,从而求得气垫导轨的阻尼系数.此外,从品质因数的角度推算阻尼系数的计算式,在阻尼很小时,该方法可视为最大速度衰减法的近似.通过气垫导轨阻尼振动实验,测量振幅、周期和光电门遮光时间等物理量,利用最大速度衰减和品质因数法得出阻尼系数的值非常接近.进一步对做阻尼振动的滑块拍摄视频,通过慢放视频得到其振动过程中振幅的衰减值,利用最大振幅衰减法计算出阻尼系数,所得结果与上述两种方法的数值符合较好,从另一个角度证明了本文提出的最大速度衰减法和品质因数法测阻尼系数的可靠性,该类方法在实验中易于操作、实践性强、所得结论可靠,为气垫导轨阻尼系数的测量提供了一种新的思路.     

Bounded perturbations of dynamics

If and are one-parameter automorphism groups of a von Neumann algebraM is said to be a bounded perturbation of if _t – _t 0 ast0. We give a complete characterization of the bounded perturbations of . In particular, we show that if can be implemented by a strongly continuous one-parameter group with self-adjoint generator (Hamiltonian)H, then can be implemented in the same way and the corresponding HamiltonianH can be chosen to be of the formH=VHV ^–1+h, whereV is a unitary ofM andh=h*M.On leave of absence from II. Institut für Theoretische Physik, Universität Hamburg, D-2000 Hamburg 50, Federal Republic of Germany     

Holographic Superconductor of Regular Phantom Black Hole

Holographic superconductors containing a non-minimal derivative coupling for the scalar field in a regular phantom plane symmetric black hole have been considered. We show that the parameter of the regular black hole b as well as the non-minimal derivative coupling parameter η affect the formation of the condensate as well as the conductivity in the superconductor. Moreover, b has a critical value in which the critical temperature T_c increases without a bound.