arXiv subjects

M. Szydlowski

Publications and source records attributed to M. Szydlowski.

4 recordsLinked to original sources

arXiv2013

Cosmology with a decaying vacuum

Properties of unstable false vacuum states are analyzed from the point of view of the quantum theory of unstable states. Some of false vacuum states survive up to times when their survival probability has a non-exponential form. At times much latter than the transition time, when contributions to the survival probability of its exponential and non-exponential parts are comparable, the survival probability as a function of time t has an inverse power-like form. We show that at this time region the instantaneous energy of the false vacuum states tends to the energy of the true vacuum state as $1/t^{2}$ for $t \to \infty$.

gr-qc↗

arXiv2012

Cosmic acceleration from modified gravity with Palatini formalism

We study new FRW type cosmological models of modified gravity treated on the background of Palatini approach. These models are generalization of Einstein gravity by the presence of a scalar field non-minimally coupled to the curvature. The models employ Starobinsky's term in the Lagrangian and dust matter. Therefore, as a by-product, an exhausted cosmological analysis of general relativity amended by quadratic term is presented. We investigate dynamics of our models, confront them with the currently available astrophysical data as well as against LCDM model. We have used the dynamical system methods in order to investigate dynamics of the models. It reveals the presence of a final sudden singularity. Fitting free parameters we have demonstrated by statistical analysis that this class of models is in a very good agreement with the data (including CMB measurements) as well as with the standard LCDM model predictions. One has to use statefinder diagnostic in order to discriminate among them. Therefore Bayesian methods of model selection have been employed in order to indicate preferred model. Only in the light of CMB data the concordance model remains invincible.

gr-qc↗

arXiv2007

Dark matter from Modified Friedmann Dynamics

The contemporary cosmic expansion is considered in the context of Modified Friedmann Dynamics (MOFD). We discuss some relativistic model exploring analogy to MOND modification of Newtonian dynamics. We argue that MOFD cosmologies can explain fraction of dark matter in the accelerating Universe. We discuss some observational constraints on possible evolutional MOFD scenarios of cosmological models coming from SN Ia distant supernovae. We show that Modified Newtonian Dynamics can be obtained as a Newtonian limit of more general relativistic models with polytropic component of Equation of State. They constitute a special subclass of generalized Cardassian models basing on generalization of the Raychaudhuri equation rather than on generalization of the Friedmann first integral. We demonstrate that MOND cosmologies are compatible with observed accelerated phase of expansion of current universe only for high value of cosmological constant. The Bayesian framework of model selection favored this model over $Λ$CDM model if $Ω_{m,o}$ is fixed but this evidence is not significant. Moreover obtained from statistical analysis value of the MOND characteristic $β$ parameter is far from value required for explanation of the flat rotation curves of spiral galaxies.

astro-ph↗

arXiv2001

Fractional Kinetics for Relaxation and Superdiffusion in Magnetic Field

We propose fractional Fokker-Planck equation for the kinetic description of relaxation and superdiffusion processes in constant magnetic and random electric fields. We assume that the random electric field acting on a test charged particle is isotropic and possesses non-Gaussian Levy stable statistics. These assumptions provide us with a straightforward possibility to consider formation of anomalous stationary states and superdiffusion processes, both properties are inherent to strongly non-equilibrium plasmas of solar systems and thermonuclear devices. We solve fractional kinetic equations, study the properties of the solution, and compare analytical results with those of numerical simulation based on the solution of the Langevin equations with the noise source having Levy stable probability density. We found, in particular, that the stationary states are essentially non-Maxwellian ones and, at the diffusion stage of relaxation, the characteristic displacement of a particle grows superdiffusively with time and is inversely proportional to the magnetic field.

physics.plasm-ph↗