8 research outputs found
Evolution of Dark Energy Perturbations for Slotheon Field and Power Spectrum
Within the framework of modified gravity model namely Slotheon model,
inspired by the theory of extra dimensions, we explore the behaviour of Dark
Energy and the perturbations thereof. The Dark Energy and matter perturbations
equations are then derived and solved numerically by defining certain
dimensionless variables and properly chosen initial conditions. The results are
compared with those for standard quintessence model and CDM model. The
matter power spectrum is obtained and also compared with that for CDM
model. It appears that Dark Energy in Slotheon model is more akin to that for
CDM model than the standard quintessence model.Comment: 20 pages LaTeX, 6 figure
Gravitational Wave Signatures from Domain Wall and Strong First-Order Phase Transitions in a Two Complex Scalar extension of the Standard Model
We consider a simple extension of Standard Model by adding two complex
singlet scalars with a symmetry. A discrete
symmetry is imposed in the model
and the added scalars acquire a non zero vacuum expectation value (VEV) when
the imposed symmetry is broken spontaneously. The real (CP even) parts of the
complex scalars mix with the SM Higgs and give three physical mass eigenstates.
One of these physical mass eigenstates is attributed to the SM like Higgs boson
with mass 125.09 GeV. In the present scenario, domain walls are formed in the
early Universe due to the breaking of discrete symmetry. In order to ensure the unstability of the
domain wall this discrete symmetry is also explicitly broken by adding a bias
potential to the Lagrangian. The unstable annihilating domain walls produce a
significant amount of gravitational waves (GWs). In addition, we also explore
the possibility of the production of GW emission from the strong first-order
phase transition. We calculate the intensities and frequencies of each of such
gravitational waves originating from two different phenomena of the early
Universe namely annihilating domain walls and strong first-order phase
transition. Finally, we investigate the observational signatures from these GWs
at the future GW detectors such as ALIA, BBO, DECIGO, LISA, TianQin, Taiji,
aLIGO, aLIGO+ and pulsar timing arrays such as SKA, IPTA, EPTA, PPTA,
NANOGrav11 and NANOGrav12.5.Comment: 30 pages, 3 figures and 5 table
Constraining PBH mass distributions from 21cm brightness temperature results and an analytical mapping between probability distribution of 21cm signal and PBH masses
The evaporation of Primordial Black Hole (PBH) via Hawking radiation
influences the evolution of Inter Galactic Medium by heating up the latter and
consequently affects the 21cm signal originated from the neutral Hydrogen
atoms. In this work, we have considered EDGES observational data of 21cm line
corresponding to cosmic dawn era to constrain the mass and the abundance of
PBHs. In this context, two different PBH mass distributions namely, power law
and lognormal mass distributions are considered to estimate the effects of PBH
evaporation on the 21cm brightness temperature . In addition to these
two mass distributions, different monochromatic masses are also considered. The
impacts of Dark Matter - baryon interactions on are also considered in
this work along with the influences of PBH evaporation. Furthermore, adopting
different monochromatic masses for PBHs, an attempt has been made to formulate
a distribution for PBH masses by associating a probability weightage of the
values (at ), within the range given by EDGES experiment,
with the calculated values for each of the PBH mass values. The
distribution best suited for the present purpose is found to be a combination
of an error function and Owen function. Allowed contours in the parameter space
of (initial PBH mass-dark matter mass) are obtained.Comment: 17 pages, 9 figure
Dark energy in light of the early JWST observations: case for a negative cosmological constant?
Early data from the James Webb Space Telescope (JWST) has uncovered the
existence of a surprisingly abundant population of very massive galaxies at
extremely high redshift, which are hard to accommodate within the standard
CDM cosmology. We explore whether the JWST observations may be
pointing towards more complex dynamics in the dark energy (DE) sector.
Motivated by the ubiquity of anti-de Sitter vacua in string theory, we consider
a string-inspired scenario where the DE sector consists of a negative
cosmological constant (nCC) and a evolving component with positive energy
density on top, whose equation of state is allowed to cross the phantom divide.
We show that such a scenario can drastically alter the growth of structure
compared to CDM, and accommodate the otherwise puzzling JWST
observations if the dynamical component evolves from the quintessence-like
regime in the past to the phantom regime today: in particular, we demonstrate
that the presence of a nCC (which requires a higher density for the evolving
component) plays a crucial role in enhancing the predicted cumulative comoving
stellar mass density. Our work reinforces the enormous potential held by
observations of the abundance of high- galaxies in probing cosmological
models and new fundamental physics, including string-inspired ingredients.Comment: 30 pages, 10 sub-figures arranged into 5 figures. v2: additional
references added, acknowledgements updated. v3: added two sub-figures (one
additional figure) and additional references. Version accepted for
publication in JCA
Addressing the high-
We consider a dark energy scenario driven by a scalar field with a pseudo-Nambu–Goldstone boson (pNGB) type potential . The pNGB originates out of breaking of spontaneous symmetry at a scale f close to Planck mass . We consider two cases namely the quintessence dark energy model with pNGB potential and the other, where the standard pNGB action is modified by the terms related to Slotheon cosmology. We demonstrate that for this pNGB potential, high-f problem is better addressed when the interaction between dark matter and dark energy is taken into account and that Slotheon dark energy scenario works even better over quintessence in this respect. To this end, a mass limit for dark matter is also estimated