3 research outputs found
The cosmology of interacting spin-2 fields
We investigate the cosmology of interacting spin-2 particles, formulating
the multi-gravitational theory in terms of vierbeins and without imposing
any Deser-van Nieuwen-huizen-like constraint. The resulting
multi-vierbein theory represents a wider class of gravitational theories if
compared to the corresponding multi-metric models. Moreover, as opposed to
its metric counterpart which in general seems to contain ghosts, it has
already been proved to be ghost-free. We outline a discussion about the
possible matter couplings and we focus on the study of cosmological scenarios
in the case
of three and four interacting vierbeins. We find rich behavior, including de
Sitter solutions
with an effective cosmological constant arising from the multi-vierbein
interaction,
dark-energy solutions and nonsingular bouncing behavior
Evading Lyth bound in models of quintessential inflation
Quintessential inflation refers to an attempt to unify inflation and late-time cosmic acceleration using a single scalar field. In this letter we consider two different classes of quintessential inflation, one of which is based upon a Lagrangian with non-canonical kinetic term k2(ϕ)∂μϕ∂μϕ and a steep exponential potential while the second class uses the concept of steep brane world inflation. We show that in both cases the Lyth bound can be evaded, despite the large tensor-to-scalar ratio of perturbations. The post-inflationary dynamics is consistent with nucleosynthesis constraint in these cases
On the possibility of blue tensor spectrum within single field inflation
We present a series of theoretical constraints on the potentially viable inflation models that might yield a blue spectrum for primordial tensor perturbations. By performing a detailed dynamical analysis we show that, while there exists such possibility, the corresponding phase space is strongly bounded. Our result implies that, in order to achieve a blue tilt for inflationary tensor perturbations, one may either construct a non-canonical inflation model delicately, or study the generation of primordial tensor modes beyond the standard scenario of single slow-roll field