Cosmology from a running vacuum model driven by a scalar field

Abstract

The possibility that the vacuum energy density ρΛ is, indeed, varying in time, has been investigated lately from the running vacuum models perspective. Motivated by such models, in the present work, we relate the decaying vacuum energy ρΛ(t) with a scalar field φ. We derive the equations of motion from such a premise and implement the first-order formalism in order to obtain analytical solutions to the cosmological parameters. We show that those are in agreement with recent Planck observational data. We discuss the physical consequences of having ρΛ(t) related to φ.

Gravitational Collapse of Anisotropic Compact Stars in Modified $ f(R) $ Gravity

“…Another possible solution is to modify the theory of general relativity. [6][7][8][9][10][11][12][13][14] One possible modification in general relativity can be achieved by modifying the Einstein-Hilbert action with additional non-linear form f (R) of the Ricci scalar R. Thus, [43]. Recently, authors have investigated three different f (R) gravity models to study the collapsing phenomena as well as the nature of central singularity [44].…”

Gravitational collapse of compact stars in $ f(R) = ξR^4 $ gravity

“…[5,6,7,8,9,10,11] One of the popular modification of general relativity is known as 𝑓 (𝑅) theory of modified gravity. [10,12,13,14,15,16] In 𝑓 (𝑅) gravity Einstein-Hilbert action is modified by introducing analytical function of curvature scalar 𝑓 (𝑅). Thus, field equations of 𝑓 (𝑅) gravity can be found by varying modified Einstein-Hilbert action.…”