In this paper we perform a dynamical analysis for a vector field as a candidate for the dark energy, in the presence of a barotropic fluid. The vector is one component of the so-called cosmic triad, which is a set of three identical copies of an abelian field pointing mutually in orthogonal directions. In order to generalize the analysis, we also assumed the interaction between dark energy and the barotropic fluid, with a phenomenological coupling. Both matter and dark energy eras can be successfully described by the critical points, indicating that the dynamical system theory is a viable tool to analyze asymptotic states of such cosmological models.

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Dynamical analysis for a vector-like dark energy

A modified-gravity-type model of two hypothetical massless vector fields is presented. These vector fields are gravitationally coupled to standard matter and an effective cosmological constant. Considered in a cosmological context, the vector fields dynamically cancel an arbitrary cosmological constant, and flat Minkowski spacetime appears as the limit of attractor-type solutions of the field equations. Asymptotically, the field equations give rise to a standard Friedmann-Robertson-Walker universe and standard Newtonian gravitational dynamics of small systems.

Possible solution to the main cosmological constant problem

Following an earlier suggestion by Dolgov, we present a model of two massless vector fields which dynamically cancel a cosmological constant of arbitrary magnitude and sign. Flat Minkowski spacetime appears asymptotically as an attractor of the field equations. Unlike the original model, the new model does not upset the local Newtonian gravitational dynamics.

Reconsidering a higher-spin-field solution to the main cosmological constant problem

We analyze the coupled quintessence in the light of the linear dynamical systems theory, with two different interactions: (1) proportional to the energy density of the dark energy and (2) proportional to the sum of the energy densities of the dark matter and dark energy. The results presented here enlarge the previous analyses in the literature, wherein the interaction has been only proportional to the energy density of the dark matter. In the first case it is possible to get the well-known sequence of cosmological eras. For the second interaction only the radiation and the dark-energy era can be described by the fixed points. Therefore, from the point of view of dynamical system theory, the interaction proportional to the sum of the energy densities of the dark matter and dark energy does not describe the universe we live in.

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Coupled quintessence and the impossibility of an interaction: a dynamical analysis study

We revise observational constraints on the class of models of modified gravity which at low redshifts lead to a power-law cosmology. To this end we use available public data on Supernova Ia and on baryon acoustic oscillations. We show that the expansion regime a(t) ~ tβ with β close to 3/2 in a spatially flat universe is a good fit to these data.

Power-law cosmology, SN Ia, and BAO

In the work , with the help of numerical simulation , the values of technological parameters are established , which provide effective two-beam laser cleaning of quartz raw materials . The optimization of two-beam laser cleaning of quartz raw materials was performed using the MOGA genetic algorithm in the ANSYS Work- bench program . Using the face-centered version of the central compositional plan of the experiment , a regression model of two-beam cleaning of quartz raw materials was obtained . The power density of a laser with the wavelength of 10.6 μm , the power density of a laser with the wavelength of 1.06 μm , the radius of a quartz particle , the radius of an impurity particle , and the processing time were used as variable factors . The maximum temperatures of quartz particles with impurities and quartz particles without impurities were used as responses . The regression model was tested . The results obtained allow us to conclude that there is a necessary correspondence between the regression model and the finite element analysis data . An assessment of the influence of processing parameters on the maximum values of the temperature of quartz particles was made . Optimization of two-beam laser cleaning of quartz raw materials was carried out according to the criterion of minimum processing time when reaching the maximum temperatures of quartz particles with an admixture of the melting temperature and limiting the maximum temperatures of quartz particles without an admixture to values below the melting temperature . Optimization was performed for two combinations of quartz and impurity particle sizes . The parameters obtained as a result of optimization and the parameters obtained as a result of finite element modeling are compared . The maximum relative error of the results obtained using the MOGA algorithm did not exceed 2.5 % when determining the maximum temperatures . As a result of the simulation , processing parameters have been established , the use of which will provide an increase in the productivity of two-beam purification of quartz raw materials . 

Optimization of Parameters of Two-Beam Laser Twelding of Quartz Raw Materials

We show by respecting the Einstein equivalence principle and general covariance in quantum theory that wave-function spreading rules out universality of free fall, and vice versa. Assuming the former is more fundamental than the latter, we gain a quantitative estimate of the free-fall non-universality, which turns out to be empirically testable in atom interferometry.

V. Emelyanov

Papers

Possible solution to the main cosmological constant problem

Reconsidering a higher-spin-field solution to the main cosmological constant problem

Optimization of Parameters of Two-Beam Laser Twelding of Quartz Raw Materials

Non-universality of free fall in quantum theory

On free fall of fermions and antifermions