Theoretical and observational bounds on some interacting vacuum energy scenarios

Bounds on Vacuum Energy Densityin a General Cosmological Scenario

General limits on the cosmological constant (or equivalently the vacuum energy density) are derived for an inflationary universe. This is accomplished under the general assumption of global hyperbolicity and without the use of any special properties like spherical symmetry or homogeneity ofthe underlying spacetime. A clear upper limit of 1/3 is obtained for the vacuum energy density parameterQ~...

Interacting realization of cosmological singularities with variable vacuum energy

We examine an interacting dark matter–variable vacuum energy model for a spatially flat Friedmann-Roberston-Walker spacetime, focusing on the appearance of cosmological singularities such as big rip, big brake, big freeze, and big separation along with abrupt events (infinite γsingularity and new w-singularity) at late times. We introduce a phenomenological interaction which has a nonlinear dep...

Interacting Energy Components and Observational H(z) Data

In this note, we extend our previous work [Phys. Lett. B 644, 7 (2007), astro-ph/0609597], and compare eleven interacting dark energy models with different couplings to the observational H(z) data. However, none of these models is better than the simplest ΛCDM model. This implies that either more exotic couplings are needed in the cosmological models with interaction between dark energy and dus...

Bounds for Incidence Energy of Some Graphs

LetG be a finite, simple, and undirected graphwith n vertices. Thematrix L(G) = D(G)−A(G) (resp., L+(G) = D(G)+A(G)) is called the Laplacianmatrix (resp., signless Laplacianmatrix [1–4]) of G, where A(G) is the adjacency matrix and D(G) is the diagonal matrix of the vertex degrees. (For details on Laplacian matrix, see [5, 6].) Since A(G), L(G) and L+(G) are all real symmetric matrices, their e...

Observational Bounds on Cosmic Doomsday