A cosmological concordance model with dynamical vacuum term

We demonstrate that creation of dark-matter particles at a constant rate implies the existence of a cosmological term that decays linearly with the Hubble rate. We discuss the cosmological model that arises in this context and test it against observations of the first acoustic peak in the cosmic microwave background (CMB) anisotropy spectrum, the Hubble diagram for supernovas of type Ia (SNIa), the distance scale of baryonic acoustic oscillations (BAO) and the distribution of large scale structures (LSS). We show that a good concordance is obtained, albeit with a higher value of the present matter abundance than in the ΛCDM model. We also comment on general features of the CMB anisotropy spectrum and on the cosmic coincidence problem.     

A model of the universe with decaying vacuum energy

The consequences of taking the total active gravitational mass of the universe phasewise constant together with a decaying vacuum energy in the background of Robertson-Walker space-time are investigated. The model so determined admits a contracted Ricci-collineation along the fluid flow vectorν ⁱ. It is geometrically closed but ever-expanding and does not possess the initial singularity, horizon, entropy, monopole or cosmological constant problems of the standard big bang cosmology. Estimates of the present matter; radiation and vacuum energy densities, the age of the universe and the present values of the deceleration parameter and the scale factor are also obtained.     

A hydrodynamic model of vacuum arc plasmas

The properties of plasmas expanding from cathode spots of vacuum arcs are calculated with a one-dimensional two-fluid model. The system of simplified hydrodynamic equations can be solved under stationary conditions using asymptotic power series. Although necessarily only an approximation, such analytical solutions prove to be advantageous compared with numerical integrations. All the plasma parameters are functions of (I/r)^2/5 (current, I: distance, r). The three forces accelerating the ions to high kinetic energies are quantitatively calculable: the electric field, the ion pressure gradient, and the electron-ion friction. The potential is decreasing towards the anode, and the residence of the plasma is negative. The ion temperature reaches only about 35% of the electron temperature. Although only asymptotic, the solution is suited to describe the arc plasma in a sufficient manner all over the expansion region     

A physical model of the low-current-density vacuum arc

A one-dimensional (1-D) physical model of the low-current-density steady-state vacuum arc is proposed. The model is based on the continuity equations for ions and electrons and the energy balance for the discharge system; the electric potential distribution in the discharge gap is assumed to be nonmonotonic. It is supposed that the ion current at the cathode is generated within the cathode potential fall region due to the ionization of the evaporated atoms by the plasma thermal electrons having Boltzmann's energy distribution. The model offers a satisfactory explanation for the principal regularities of a hot-cathode vacuum arc with diffuse attachment of the current. The applicability of the model proposed to the explanation of some processes occurring in a vacuum arc, such as the flow of fast ions toward the anode, the current cutoffs and voltage bursts, and the backward motion of a cathode spot in a transverse magnetic field is discussed     

A model for a uniform steady-state vacuum arc with a hot anode

A model is formulated and evaluated for a Uniform electrical discharge sustained in vapor evaporated from an arc-heated anode. The plasma potential is positive with respect to both the cathode and anode. For a Cu anode, the anodic vapor dominates the plasma for current densities exceeding 8 kA/m². The anode heating potential is approximately 6.5 V, and the dominant cooling mechanism is evaporation for current densities exceeding 20 kA/m². Over the range 10 to 10000 kA/m², the electron density increases from 8×10¹⁷ to 5×10²³ m^-3, while the ionization fraction rises from 0.3% to 4%. At the lower end of this current range the electrical resistivity of 4 mΩ-m is determined primarily by electron-neutral collisions, while with increasing current the resistivity decreases to 0.7 mΩ-m, with electron-ion collisions contributing an equal share. This hot-anode vacuum arc may have potential for industrial application as a macroparticle-free high-deposition-rate coating source     

A revised theoretical model of vacuum arc spot plasmas

The quasi-stationary hemispherical expansion of the cathodic plasma in vacuum arcs can be modeled with hydrodynamic two-fluid equations. In any case, the state of the plasma is determined by the only variable (I/r)^2/5 (with current I , distance r). In order to avoid some deficiencies of the model (as published) and to investigate more carefully the dependence of the plasma parameters on the arc current, the known analytic solution to the problem is improved by taking into consideration the variability of the Coulomb logarithm and the dependence of the boundary conditions on I. These effects are treated separately. Examples are used to illustrate the new results, with particular emphasis on ion acceleration. The influence of the above factors turns out to be rather unimportant. Quantitatively, they cause some shifts, but no qualitative change of the basic behavior of the plasma is seen     

Hadron model with braking of spatial homogeneity of vacuum

A possibility of breaking spatial homogeneity of vacuum as a result of interaction of a quark with a Bose field has been investigated. It is shown that there can be in a ground state of the wave-packet type. The energetic conditions for such a state have been found. The origin of deep inelastic processes and the phenomenon of quark confinement are discussed.     

Exact Bianchi type-V vacuum model

An exact Bianchi type-V vacuum solution is presented corresponding to which the equations of motion are solved exactly for the coordinates of the null geodesics.     

A Savvidy vacuum with center vortices

The one loop SU(2) effective potential of a constant chromomagnetic field and thin vortex has been obtained using the background field method in the scope of the Yang–Mills theory. The possible relationship between a Savvidy vacuum and a spaghetti vacuum is discussed.     

Observational constraints on running vacuum model

We investigate the power spectra of the CMB temperature and matter density in the running vacuum model(RVM) with the time-dependent cosmological constant of A=3 vH~2+ Λ_0, where H is the Hubble parameter. In this model, dark energy decreases in time and decays to both matter and radiation. By using the Markov chain Monte Carlo method, we constrain the model parameter v as well as the cosmological observables. Explicitly, we obtain v ≤1.54× 10~(-4)(68% confidence level) in the RVM with the best-fit χ_(RVM)~2 =13968.8, which is slightly smaller thanχ_(ΛCDM)~2= 13969.8 in the ΛCDM model of v = 0.     

A vacuum spacetime with closed null geodesics

Here we present a vacuum spacetime with closed null geodesics (CNGs). These CNGs are obtained by analytically solving the geodesic equations. This spacetime is locally isometric to the plane wave spacetime and has very different global properties from metrics of the latter type.     

Multi-skyrmion states in the Skyrme model with a false vacuum potential

We study multi-skyrmion states using the Skyrme model with a false vacuum potential up to baryon number B=8 using the product ansatz.It is found that both the false and true vacuum potentials can result in a cluster structure for the multi-skyrmion states.We also analyze the effect of explicit chiral breaking on the masses and contour surfaces of the baryon number density of the multi-skyrmion states.     

Cosmological model with dynamical cancellation of vacuum energy and dark energy

We propose a model with a compensating scalar field whose back reaction to the cosmological curvature cancels possible vacuum energy density down to the terms of the order of the time-dependent critical energy density. Thus, the model simultaneously solves the mystery of the compensation of vacuum energy with an accuracy of 120 orders of magnitude and explains the existence of the observed dark energy. At an early stage, the suggested cosmological model might experience exponential expansion without an additional inflaton field. However, the solution found is unstable with respect to small perturbations. The stability can be ensured by introducing nonanalytical terms depending upon the absolute value of the curvature scalar R. Unfortunately, stable solutions do not describe realistic cosmology at the matter-dominated stage.     

Critical slowing down in a bistable model with squeezed vacuum environment

Critical slowing down effect in a bistable model of a two-level atomic medium in a ring cavity and in contact with squeezed vacuum field is examined within the mean field approximations in the high-, low- and arbitrary-Q cavity cases. Depending on the squeezed vacuum field phase parameter, the time response to linear perturbation of the incident field near the swtiching-on point can be enhanced or reduced compared with the normal vacuum case. In the low-Q cavity case with atomic collisional broadening switching time is both increased and become insensitive to the phase of the squeezed vacuum field. Analytical expressions are given and analysed for the critical (extermal) values of the incident field. In the high-Q cavity, Gaussian field feature causes lesser-steep transition between the stable states in both the normal and squeezed vacuum cases.Received: 25 April 2004, Published online: 24 August 2004PACS: 42.65.Pc Optical bistability, multistability, and switching, including local field effects - 42.65.-k Nonlinear optics     

HMO model of scalar field in vacuum

In this paper, the HMO model of scalar field in vacuum is developed using the covariant field theory, in which the so-called current density and mass density of optical fluid are obtained and analyzed.     

Comment on the Bianchi type-V vacuum model

It is shown that the nonlocally rotationally symmetric Bianchi type-V vacuum solution recently discussed by Nayak is identical, after trivial transformations, with the solution found some years ago by Joseph. In addition some calculations and remarks concerning the integration of the null geodesic equations are given.     

Self-consistent Gaussian model of nonperturbative QCD vacuum

We show that the minimal Gaussian model of nonlocal vacuum quark and quark-gluon condensates in QCD violates the transverse character of the correlator of two vector currents. We suggest the improved Gaussian model of the nonperturbative QCD vacuum, which respects QCD equations of motion and minimizes the revealed gauge-invariance breakdown. We obtain the refined values of pion distribution amplitude (DA) conformal moments 〈ξ^2N 〉_π (N = 1, ..., 5) using the improved QCD vacuum model, including the inverse moment 〈x ^?1〉_π, being inaccessible if one uses the standard QCD SR. We construct the allowed region for Gegenbauer coefficients a ₂ and a ₄ of the pion DA for two values of the QCD vacuum nonlocality parameter, λ _q ² = 0.4 and 0.5 GeV².     

HMO model of scalar field in vacuum

In this paper, the HMO model of scalar field in vacuum is developed using the covariant field theory, in which the so-called current density and mass density of optical fluid are obtained and analyzed.     

Non-trivial Fock vacuum of the light-front Schwinger model

A Fock representation for the physical vacuum based on the dynamical zero mode of the gauge field is suggested for the Schwinger model quantized on the light front. The θ-vacuum in terms of a gauge invariant superposition of zero-mode coherent states is shown to reproduce the vacuum-angle dependence of the fermion condensate within the bosonized formulation of the model.