108 research outputs found
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 ) 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
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