Reanalyzing the upper limit on the tensor-to-scalar perturbation ratio r_T in a quartic potential inflationary model

We study the polynomial chaotic inflation model with a single scalar field in a double well quartic potential which has recently been shown to be consistent with Planck data. In particular, we study the effects of lifting the degeneracy between the two vacua on the inflationary observables, i.e. spectral index n_s and tensor-to-scalar perturbation ratio r_T. We find that removing the degeneracy allows the model to satisfy the upper limit constraints on r_T from Planck data, provided the field starts near the local maximum. We also calculate the scalar power spectrum and non-Gaussianity parameter f_NL for the primordial scalar perturbations in this model.Comment: 7 pages, 7 figures; v2: discussion added, submitted to Phys. Lett. B; v3: published versio

Studies in Structure Formation in theories with a repulsive long range gravitational force

This article reports on emergence of structures in a class of alternative theories of gravity. These theories do not have any horizon, flatness, initial cosmological singularity and (possibly) quantization problems. The model is characterised by a dynamically induced gravitational constant with a ``wrong'' sign corresponding to repulsive gravitation on the large scale. A non - minimal coupling of a scalar field in the model can give rise to non - topological solitons in the theory. This results in domains (gravity - balls) inside which an effective, canonical, attractive gravitational constant is induced. We consider simulations of the formation and evolution of such solutions. Starting with a single gravity - ball, we consider its fragmentation into smaller (lower mass) balls - evolving by mutual repulsion. After several runs, we have been able to identify two parameters: the strength of the long range gravitational constant and the size of the gravity balls, which can be used to generate appropriate two point correlations of the distribution of these balls.Comment: Normal Tex, 7 pages, 5 figures available from the author

Cosmological Tests for a Linear Coasting Cosmology

A strictly linear evolution of the scale factor is a characteristic feature in several classes of alternative gravity theories, as also in the standard (big-bang) model with specially chosen matter equation of state. In this article we report that this model is consistent with gravitational lensing statistics (within $1\sigma$) and accomodates old high-redshift galaxies. We finally conclude that linear coasting cosmology, \a(t) = t, is not ruled out basis of these observational tests