There have been several suggestions of the existence of cosmological redshift signatures in the temporal and spectral characteristics of gamma-ray bursts. However, recent discoveries of afterglows and redshift measurements indicate the presence of broad “luminosity functions” which may overwhelm such weaker cosmological signatures. The primary goal of this paper is to determine if the intrinsic...

I review the recent 5D self-tuning solutions of the cosmological constant problem, and try to unify two cosmological constant problems within the framework of the self-tuning solutions. One problem, the large cosmological constant needed for inflation, is interpreted by starting with the parameters allowing only the dS vacuum, and the vanishing cosmological constant at a true vacuum is realized...

The magnitude-redshift relation is one of the tools for a direct observational approach to cosmology. The discovery of high redshift Type Ia supernovae (SNIa) and their use as “standard candles” has resurrected interest in this approach. Recently collected data have been used to address the problem of measuring the cosmological parameters of the universe. Analysed in the framework of homogeneou...

We study Abelian strings in a fixed de Sitter background. We find that the gauge and Higgs fields extend smoothly across the cosmological horizon and that the string solutions have oscillating scalar fields outside the cosmological horizon for all currently accepted values of the cosmological constant. If the gauge to Higgs boson mass ratio is small enough, the gauge field function has a power-...

In this paper we provide both a diagnosis and resolution of the cosmological constant problem, one in which a large (as opposed to a small) cosmological constant Λ can be made compatible with observation. We trace the origin of the cosmological constant problem to the assumption that the local gravitational Newton constant G (as measured in a Cavendish experiment) sets the scale for global cosm...

Inspired by the recent conjecture originated from graduated dark energy that Universe has recently transitioned anti-de Sitter vacua to de vacua, we extend $\Lambda$CDM model a cosmological constant ($\Lambda_{\rm s}$) switches sign at certain redshift $z_\dagger$, and call this $\Lambda_{\rm s}$CDM. We discuss construction theoretical features of find out that, when consistency s}$CDM with CMB...

We want to study the perturbation growth of an initial seed of an ellipsoidal shape in Top-Hat collapse model of the structure formation in the Modied Chaplygin gas cosmology. Considering reasonable values of the constants and the parameters of the model under study, we can show that a very small deviation from spherical symmetry (ellipsoidal geometry) in the initial seed leads to a nal highly ...