Generation of a Dark Hollow Beam inside a Cavity

A new method is introduced to generate a hollow beam inside a cavity.Using a matrix eigenvalue method,the laser resonator with optical diffraction elements is theoretically analysed and simulated.The hollow beam can be obtained theoretically by controlling the parameters of the diffraction functions.After designed the diffraction components in the cavity,a hollow beam of good quality is realized experimentally using a YAG solid state laser.     

Is Galaxy Dark Matter a Property of Spacetime?

We describe the motion of a particle in acentral field in an expanding universe. Use is made ofa double expansion in 1/c and 1/, where c and are the speed of light and the Hubble time. In thelowest approximation the rotational velocity is shownto satisfy v⁴ = 2/3 GMcH₀, whereG is Newton's gravitational constant, M is the mass ofthe central body (galaxy), and H₀ is theHubble constant. This formula satisfies observations of stars moving inspiral and elliptical galaxies, and is in accordancewith the familiar Tully–Fisher law.     

Dynamics of Two Dark Solitons in a Polariton Condensate

We theoretically investigate dynamics of two dark solitons in a polariton condensate under nonresonant pumping,based on driven dissipative Gross–Pitaevskii equations coupled to the rate equation. The equation of motion of the relative center position of two-dark soliton is obtained analytically by using the Lagrangian approach. In particular, the analytical expression of the effective potential between two dark solitons is given. The resulting equation of motion captures how the open-dissipative...     

Six-Fold Degenerate Dark States in a Four-Level Atomic System

With all driving fields on Raman resonance, a tripod-type atomic system quickly evolves into a dark state decoupled from the lossy excited level. The dark state depends strongly on field Rabi frequencies, spontaneous decay rates, and the initial atomic population in a complicated way. Analytical results reveal that it is a sixfold degenerate dark state with its three components superposed both coherently and incoherently due to population redistribution from spontaneous emission.     

Dark periods in the resonance fluorescence of a single Λ system

We use the quantum jump method to study the photon statistics of a single laser-driven atom in the configuration where both lower levels are strongly coupled to the common upper level. Under certain conditions we show that, for almost degenerate lower levels, light and dark periods occur which are similar to those of the well-known Dehmelt V system. Analytic results for their mean lengths and other statistical properties are given. For large separation of the lower levels we prove an interesting bunching property by the photons in the resonance fluorescence near the dark resonance. We propose a realistic system for which these effects may be observed.     

Holographic Dark Energy in a Non-flat Universe with Granda-Oliveros Cut-off

Motivated by Granda and Oliveros (GO) model, we generalize their work to the non-flat case. We obtain the evolution of the dark energy density, the deceleration and the equation of state parameters for the holographic dark energy model in a non-flat universe with GO cut-off. In the limiting case of a flat universe, i.e. k=0, all results given in GO model are obtained.     

Can Inflation, Dark Matter and Dark Energy Be Described in Terms of a Single, Real Scalar Field?

In this article, our aim is to consider inflation, dark energy and dark matter in the framework of a real scalar field. To this end, we use the quintessence approach. We have tried a real scalar field with a specific self-interaction potential in a spacially flat universe. Numerical results indicate that this potential can drive the expansion of the universe in three distinct phases. The first phase behaves as an inflationary expansion. For this stage, setting the scalar field’s initial value to ϕ ₀≥1.94 leads to N 3 68\mathcal{N}\geq 68 favored by observation. After the inflationary phase, the scalar field starts an oscillatory behavior which averages to a =0\bar{w}=0 fluid. This stage can be taken as a cold dark matter (p≈0) epoch expected from works on the structure formation issue. Observations and cosmological models indicate that t _inf ≈10⁻³⁵ s and the matter dominated lasts for t _m ≈10¹⁷ s, hence (\fract_mt_inf)_obs ? 10⁵²(\frac{t_{m}}{t_{inf}})_{obs}\approx10^{52}. We have shown that the present model can satisfy such a constraint. Finally, the scalar field leaves the oscillatory behavior and once again enters a second inflationary stage which can be identified with the recent accelerated expansion of the universe. We have also compared our model with the ΛCDM model and have found a very good agreement between the equation of state parameter of both of models during the DM and DE era.     

Ultraslow Bright and Dark Solitons Using only a Pulsed Laser in a Cold Three-State Medium

We demonstrate the efficient generation of ultraslow bright and dark optical solitons in a lifetime-broadened three-level atomic medium by using only a low-intensity pulsed laser radiation. The proposed scheme may be useful, in principle, for the control technology of optical delay lines and optical buffers.     

Dark Energy Coupled with Dark Matter in the Accelerating Universe

To model the observed Universe containing both dark energy and dark matter, we study the effective Yang-Mills condensate model of dark energy and add a non-relativistic matter component as the dark matter, which is generated out of the decaying dark energy at a constant rate Г, a parameter of our model. For the Universe driven by these two components, the dynamic evolution still has asymptotic behaviour: the expansion of the Universe is accelerating with an asymptotically constant rate H, and the densities of both components approach to finite constant values. Moreover, Ω△～ 0.7 for dark energy and Ωm～0.3 for dark matter are achieved if the decay rate Г is chosen such that Г/H ～ 1.     

Dark Energy Coupled with Relativistic Dark Matter in Accelerating Universe

Recent observations favour an accelerating Universe dominated by the dark energy. We take the effective Yang-Mills condensate as the dark energy and couple it to a relativistic matter which is created by the decaying condensate. The dynamic evolution has asymptotic behaviour with finite constant energy densities, and the fractional densities Ω∧ ～0.7 for dark energy and Ωm ～ 0.3 for relativistic matter are achieved at proper values of the decay rate. The resulting expansion of the Universe is in the de Sitter acceleration.     

Analysis of Possible Evolution of Dark Energy by Using a Power Series

We simulate the density of dark energy by using a power series to analyse the possible evolution of dark energy. The parameters are constrained from the newly released Cold sample of the supernova dataset. The evolutions of dark energy, as the power series from two free parameters to five free parameters, have the common and the different characters. We may conclude that either the density of dark energy possibly oscillates or increases after it decreases to a minimum value. Accordingly, the state equation of dark energy oscillates or evolves from ωde〉 -1 in the past to ωee〈 -1 around the present epoch.     

Switching and Self-trapping Dynamics of Dark Solitons in a Two-Component Bose-Einstein Condensate

Two coupled dark solitons are considered in a two-component Bose-Einstein condensate, and their dynamics are investigated by the variational approach based the renormalized integrals of motion. The stationary states as physical solutions to the describing equations are obtained, and the dynamic mechanism is demonstrated by performing a coordinate of a classical particle moving in an effective potential field. The switching and selftrapping dynamics of the coupled dark vector solitons are discussed by the evolution of the atom population transferring ratio.     

Can a Higgs portal Dark Matter be compatible with the anti-proton cosmic-ray?

Recent direct detection experiments of Dark Matter (DM), CoGeNT and DAMA implicate a light DM of a few GeV. Such a light DM would generate a large amount of anti-proton since suppression for anti-proton flux from DM annihilation is ineffective. We discuss whether a light dark matter with mass of 5–15 GeV, which is especially in favor of the recent experiments reported by CoGeNT, is compatible with the anti-proton no excess in the cosmic-ray. In view of the direct detection of DM and no anti-proton excess in the cosmic-ray both, we show that a Dirac DM is favored than a scalar one since there is no s-wave of the annihilation cross section for the Dirac DM. A large elastic cross section for direct detection can be obtained through the additional light Higgs exchange. We show an allowed region that simultaneously satisfies the DM relic density, the elastic cross section favored by CoGeNT and also the constraint of _HLZZ$H_{L}ZZ$ coupling of the light Higgs boson by LEP.     

Dark halo or bigravity?

Observations show that about the of the Universe iscomposed by invisible (dark) matter (DM), for which manycandidates have been proposed. In particular, the anomalousbehavior of rotational curves of galaxies (i.e. theflattening at large distance instead of the Keplerian fall)requires thatthis matter is distributed in an extended halo around the galaxy. In order to reproduce this matter density profiles in Newtonian gravity and in cold dark matter (CDM) paradigm (in which theDM particles are collisionless), many ad-hoc approximations are required.The flattening of rotational curves can be explained by asuitable modification of gravitational force in bigravity theories, together with mirror matter model that predicts the existenceof a dark sector in which DM has the same physical properties of visible matter.As an additional result, the Newton constant is different at distances much less and much greater than 20 kpc.     

Retardation Effects for “Dark” Plasma Modes in a Two-Dimensional Electron System

JETP Letters - Plasma excitations with different symmetries in a single two-dimensional electron disk are studied by optical detection of resonant microwave absorption. The manifestation of...     

Theoretical Analysis and Experimental Study on Generation of a Dark Hollow Beam by a Micron-sized Hollow Optical Fiber

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Gravitational Collapse with Dark Energy and Dark Matter in Hořava-Lifshitz Gravity

In this work, the collapsing process of a spherically symmetric star, made of dust cloud, is studied in Ho?ava Lifshitz gravity in the background of Chaplygin gas dark energy. Two different classes of Chaplygin gas, namely, New variable modified Chaplygin gas and generalized cosmic Chaplygin gas are considered for the collapse study. Graphs are drawn to characterize the nature and to determine the possible outcome of gravitational collapse. A comparative study is done between the collapsing process in the two different dark energy models. It is found that for open and closed universe, collapse proceeds with an increase in black hole mass, the only constraint being that, relatively smaller values of Λ has to be considered in comparison to λ. But in case of flat universe, possibility of the star undergoing a collapse in highly unlikely. Moreover it is seen that the most favourable environment for collapse is achieved when a combination of dark energy and dark matter is considered, both in the presence and absence of interaction. Finally, it is to be seen that, contrary to our expectations, the presence of dark energy does not really hinder the collapsing process in case of Ho?ava-Lifshitz gravity.     

A Modified Generalized Chaplygin Gas as the Unified Dark Matter–Dark Energy Revisited

A modified generalized Chaplygin gas (MGCG) is considered as the unified dark matter–dark energy revisited. The character of MGCG is endued with the dual role, which behaves as matter at early times and as a quiessence dark energy at late times. The equation of state for MGCG is p?=???αρ/(1?+?α)????(z)ρ ^???α /(1?+?α) , where $\vartheta(z)=-[\,\rho_{\,\rm 0c}(1+z)^{3}]\,^{(1+\alpha)}(1-\Omega_{\,\rm 0B})^{\alpha}\{\alpha\Omega_{\,\rm 0DM}+ \Omega_{\,\rm 0DE}[\,\omega_{\,\rm DE}+\alpha(1+\omega_{\rm DE})](1+z)^{3\omega_{\rm DE}(1+\alpha)}\}$ . Some cosmological quantities, such as the densities of different components of the universe Ω _i (i, respectively, denotes baryons, dark matter, and dark energy) and the deceleration parameter q, are obtained. The present deceleration parameter q ₀, the transition redshift z _T, and the redshift z _eq, which describes the epoch when the densities in dark matter and dark energy are equal, are also calculated. To distinguish MGCG from others, we then apply the Statefinder diagnostic. Later on, the parameters (α and ω _DE) of MGCG are constrained by combination of the sound speed $c^{2}_{\rm s}$ , the age of the universe t ₀, the growth factor m, and the bias parameter b. It yields $\alpha=-3.07^{+5.66}_{-4.98}\times10^{-2}$ and $\omega_{\rm DE}=-1.05^{+0.06}_{-0.11}$ . Through the analysis of the growth of density perturbations for MGCG, it is found that the energy will transfer from dark matter to dark energy which reach equal at z _eq～0.48 and the density fluctuations start deviating from the linear behavior at z～0.25 caused by the dominance of dark energy.     

Dark soliton in one-dimensional Bose–Einstein condensate under a periodic perturbation of trap

The perturbation of a confining trap leads to the collective oscillation of a Bose--Einstein condensate, thereby the propagation of a dark soliton in the condensate is affected. In this study, periodic perturbation is employed to match the soliton oscillation. We find that the soliton dynamics depends sensitively on the coupling between the moving direction of the trap and that of the soliton. The soliton energy/depth evolves periodically, and a relevant shift in the soliton trajectory occurs as compared with the unperturbed case. Overall, the soliton oscillation frequency changes little even if the perturbation amplitude and frequency vary.     

A Possible Origin of Dark Energy

We discuss the possibility that the existence of dark energy may be due to the presence of a spin zero field φ(χ),either elementary or composite. In the presence of other matter field, the transformation φ(χ)→φ(χ)＋constant can generate a negative pressure, like the cosmological constant. In this picture, our universe can be thought asa very large bag, similar to the much smaller MIT bag model for a single nucleon.