26 research outputs found
Warming up D3 brane motion in the background of D5 brane and Inflation
The position of a mobile D-3 brane moving towards a stack of localized D-5
branes has been studied as a candidate driving inflation in the warm
inflationary scenario. We compare the results obtained by considering the
dissipation parameter as an arbitrary function of only the inflaton
field and a particular form derived by Bastro-Gil et al \cite{Berera8}. We find
that the observables remain well within the recent observational constraint for
a wide range of model parameters for the first case whereas the spectral index
in the later case is always predicted blue, other cosmological observables
remaining well within bound for a wider range of parameters though. We also
discuss the non-gaussianity generated during inflation in this model.Comment: 13 pages, 4 figures. A new section has been incorporate
Tideless traversable wormholes in General Relativity and modified gravity with a Kalb-Ramond background
Among the several modified/extended gravity paradigms, the concept of
antisymmetric connections leading to space-time torsion can be traced back to
Cartan. More recently, developments in string theory have suggested the
existence of a rank-2 self-interacting tensor field called the Kalb-Ramond
field with similar outcomes, the field strength of which can support analytic
wormhole-like solutions. In this study, we comprehensively probe the existence
of traversable Morris-Thorne like wormhole solutions sourced by the Kalb-Ramond
field strength in both General Relativity (GR) and and modified
gravity. We evaluate wormhole shape functions and analyze the energy conditions
near the throat, check the stability using the generalized
Tolman-Oppenheimer-Volkov equations, and demonstrate the possibility of minimum
exotic matter by numerically estimating the volume integral quantifier. Our
results show the existence of stable wormhole solutions in GR and a simple
gravity model, and unstable ones in a power-law type gravity
model.Comment: 26 Pages, 19 Figures, 1 Tabl
Traversable wormholes in gravity sourced by a cloud of strings
Wormhole solutions in General Relativity (GR) require \textit{exotic} matter
sources that violate the null energy condition (NEC), and it is well known that
higher-order modifications of GR and some alternative matter sources can
support wormholes. In this study, we explore the possibility of formulating
traversable wormholes in modified gravity, which is perhaps the most
widely discussed modification of GR, with two approaches. First, to investigate
the effects of geometrical constraints on the global characteristics, we gauge
the -component of the metric tensor, and employ Pad\`{e} approximation to
check whether a well-constrained \textit{shape function} can be formulated in
this manner. We then derive the field equations with a background of string
cloud, and numerically analyse the energy conditions, stability, and amount of
exotic matter in this space-time. Next, as an alternative source in a simple
gravity model, we use the background cloud of strings to estimate the
wormhole shape function, and analyse the relevant properties of the space-time.
These results are then compared with those of wormholes threaded by normal
matter in the simple gravity model considered. The results demonstrate
that wormholes with NEC violations are feasible; however, the wormhole
space-times in the simple gravity model are unstable
Warm Inflation in gravity
In this work, we explored warm inflation in the background of
gravity in the strong dissipation regime. Considering scalar field for FLRW
universe, we derived modified field equations. We then deduced slow-roll
parameters under slow-roll approximations followed by power spectrum for scalar
and tensor perturbations and their corresponding spectral indices. We have
considered Chaotic and Natural potentials and estimated scalar spectral index
and tensor-to-scalar ratio for constant as well as variable dissipation factor
. We found that both the rejected potentials can be revived under the
context of gravity with suitable choice of the model parameters.
Further, it is seen that within the warm inflationary scenario both the
potentials are consistent with Planck 2018 bounds at the Planckian and sub
Planckian energy scales.Comment: 19 pages, 5 figure