Nonlinear Schrödinger-type formulation of scalar field cosmology: Two barotropic fluids and exact solutions

Time-independent nonlinear Schrödinger-type (NLS) formulation of FRW cosmology with canonical scalar field is considered in the case of two barotropic fluids. We derived Friedmann formulation variables in terms of NLS variables. Seven exact solutions found by D’Ambroise [Ph.D. thesis, arXiv:1005.1410 ] and one new found solution are explored and tested in cosmology. The result suggests that time-independent NLS formulation of cosmology case should be upgraded to the time-dependent case.

Applying He's variational iteration method to FRW cosmology

This work is devoted to the investigation of Friedmann-Robertson-Walker (FRW) cosmological models with the help of the so-called Variational Iteration Method (VIM). For this end, we briefly recall the main equations of the cosmological models and the basic idea of VIM. In order to approbate the VIM in FRW cosmology and demonstrate the main steps in solving by this method, we consider the test example of the universe with dust for which the exact solution of the model is known. Then, a solution for the spatially flat FRW model of the universe filled with the dust and quintessence is obtained when the exact analytic solution cannot be found. A comparison of our solution with the corresponding numerical solution shows that it is of a high degree of accuracy. Moreover, the Dynamical System Analysis to the dynamics of the homogeneous and isotropic FRW universes is used as a special case of generalized Lotka–Volterra system where the competitive species are the barotropic fluids filling the Universe. With the help of VIM, we have found the iterative formulae for the density parameters of the cosmological analog of the generalized Lotka–Volterra set of equations. All solutions illustrated graphically by means of Maple software.

Evolution of thin shells in D-dimensional general relativity

In this paper, we consider singular timelike spherical hypersurfaces embedded in a [Formula: see text]-dimensional spherically symmetric bulk spacetime which is an electrovacuum solution of Einstein equations with cosmological constant. We analyze the different possibilities regarding the orientation of the gradient of the standard [Formula: see text] coordinate in relation to the shell. Then we study the dynamics according to Einstein equations for arbitrary matter satisfying the dominant energy condition. In particular, we thoroughly analyze the asymptotic dynamics for both the small and large-shell-radius limits. We also study the main qualitative aspects of the dynamics of shells made of linear barotropic fluids that satisfy the dominant energy condition. Finally, we prove weak cosmic censorship for this class of solutions.

The Modified Quasi-geostrophic Barotropic Models Based on Unsteady Topography

New models using scale analysis and perturbation methods were derivated starting from the shallow water equations based on barotropic fluids. In the paper, to discuss the irregular topography with different magnitudes, especially considering the condition of the vast terrain, some modified quasi-geostrophic barotropic models were obtained. The unsteady terrain is more suitable to describe the motion of the fluid state of the earth because of the change of global climate and environment, so the modified models are more rational potential vorticity equations. If we do not consider the influence of topography and other factors, the models degenerate to the general quasi-geostrophic barotropic equations in the previous studies. Modelos semigeostróficos barotrópicos modificados con base en topografía inestableResumenEste trabajo deduce nuevos modelos con el uso de los métodos de análisis a escala y de perturbación a partir de las ecuaciones de aguas poco profundas con base en fluidos barotrópicos. En este artículo se obtuvieron algunos modelos semigeostróficos barotrópicos para aplicar en zonas de topografía inestable con diferentes magnitudes y considerar especialmente la condición del extenso terreno. La topografía inestable es más propicia para describir el movimiento del estado fluido de la tierra debido al cambio del clima y ambiente, por lo tanto los modelos modificados son ecuaciones de vorticidad potenciales más razonables. Si no se considera la influencia de la topografía y otros factores, los modelos se reducirían a las ecuaciones generales semigeostróficas barotrópicas de estudios anteriores.