In this paper, we propose a simple parametrization of the Hubble parameter H in order to explain the late time cosmic acceleration. We show that our proposal covers many models obtained in different schemes of parametrization under one umbrella. We demonstrate that a simple modification in the functional form of Hubble parameter can give rise to interesting cosmological phenomena such as big rip singularity, bounce and others. We have also constrained the model parameters using the latest 28 points of H(z) data for three cases which admit transition from deceleration to acceleration.Comment: 24 pages, 5 figure

In this paper, we analyzed inflation from k-essence in the framework of Horndeski gravity. In the specific, we considered models of canonical scalar field and k-essence with quadratic kinetic term. Viable inflationary models can be reconstructed by starting from the cosmological data. Several possibilities are explored in order to correctly reproduce the spectral index and the tensor-to-scalar ratio of primordial cosmological perturbations.

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We consider inhomogeneous viscous fluids in flat Friedmann-Robertson-Walker universe. We analyze different kinds of such fluids and investigate the possibility to reproduce the current cosmic acceleration providing a different future evolution with respect to the Cosmological Constant case. In particular, we study the presence of finite-future time singularities. We also discuss a general class of "integrable" viscous fluid models whose bulk viscosities obey to a common differential equation. *

We construct a plane symmetric, standing gravitational wave for a domain wall plus a massless scalar field. The scalar field can be associated with a fluid which has the properties of ''stiff'' matter, i.e., matter in which the speed of sound equals the speed of light. Although domain walls are observationally ruled out in the present era, the solution has interesting features which might shed light on the character of exact nonlinear wave solutions to Einstein's equations. Additionally this solution may act as a template for higher dimensional ''brane-world'' model standing waves.