A5088528226- Cosmology and Gravitation Theories
- Galaxies: Formation, Evolution, Phenomena
- Black Holes and Theoretical Physics
- Dark Matter and Cosmic Phenomena
- Solar and Space Plasma Dynamics
- Radio Astronomy Observations and Technology
- Geophysics and Gravity Measurements
- Astronomy and Astrophysical Research
- Particle physics theoretical and experimental studies
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Computational Physics and Python Applications
- Advanced Differential Geometry Research
- Relativity and Gravitational Theory
- Pulsars and Gravitational Waves Research
- Noncommutative and Quantum Gravity Theories
- Stochastic processes and financial applications
- Scientific Research and Discoveries
- Complex Systems and Time Series Analysis
- Advanced Thermodynamics and Statistical Mechanics
- Indian Economic and Social Development
- South Asian Studies and Conflicts
- High-Energy Particle Collisions Research
- Scientific Computing and Data Management
- Politics and Conflicts in Afghanistan, Pakistan, and Middle East
Jamia Millia Islamia
2016-2025
Ahmedabad University
2021-2022
Asia Pacific Center for Theoretical Physics
2015
The Abdus Salam International Centre for Theoretical Physics (ICTP)
2010
Universitat Autònoma de Barcelona
2009
Instituto Politécnico de Lisboa
2003-2006
Instituto Superior Técnico
2002-2006
Vanderbilt University
2005-2006
Heidelberg University
2006
University of Lisbon
2004-2006
We consider the scenario emerging from dynamics of a generalized $d$-brane in $(d+1, 1)$ spacetime. The equation state describing this system is given terms energy density, $ρ$, and pressure, $p$, by relationship $p = - A/ρ^α$, where $A$ positive constant $0 < α\le 1$. discuss conditions under which homogeneity arises show that describes evolution universe evolving phase dominated non-relativistic matter to cosmological via an intermediate period effective αρ$.
Abstract Early data from the James Webb Space Telescope (JWST) has uncovered existence of a surprisingly abundant population very massive galaxies at extremely high redshift, which are hard to accommodate within standard ΛCDM cosmology. We explore whether JWST observations may be pointing towards more complex dynamics in dark energy (DE) sector. Motivated by ubiquity anti-de Sitter vacua string theory, we consider string-inspired scenario where DE sector consists negative cosmological...
This paper introduces the class of omnipotent dark energy (DE) models characterized by nonmonotonic densities that are capable attaining negative values with corresponding equation state parameters featuring phantom divide line (PDL) crossings and singularities. These nontrivial features phenomenologically motivated findings previous studies reconstruct cosmological functions from observations, success extensions $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, whose actual or effective DE...
The $\ensuremath{\sim}5\ensuremath{\sigma}$ mismatch between the value of Hubble parameter measured by SH0ES and one inferred from inverse distance ladder (IDL) constitutes biggest tension afflicting standard model cosmology, which could be pointing to need physics beyond $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$. In this paper, we study background history required solve ${H}_{0}$ if consider prerecombination physics, paying special attention role played data on baryon acoustic...
Abstract Early observations with the James Webb Space Telescope (JWST) have revealed existence of an unexpectedly large abundance extremely massive galaxies at redshifts z ≳ 5: these are in tension predictions not only standard ΛCDM cosmology, but also those a wide class dynamical dark energy (DE) models, and generally better agreement models characterized by phantom behaviour. Here we consider model, inspired string theory ubiquity anti-de Sitter vacua therein, featuring evolving DE...
We study the dependence of location cosmic microwave background radiation peaks on parameters generalized Chaplygin gas model, whose equation state is given by $p=\ensuremath{-}A/{\ensuremath{\rho}}^{\ensuremath{\alpha}},$ where A a positive constant and $0<\ensuremath{\alpha}<~1.$ find, in particular, that observational data arising from Archeops, BOOMERANG, supernova high-redshift observations allow constraining significantly parameter space model. Our analysis indicates emerging model...
The generalized Chaplygin gas (GCG) model explains the recent accelerated expansion of Universe via an exotic background fluid whose equation state is given by p=−A/ρα, where A a positive constant and 0<α⩽1. interesting alternative to scenarios involving scalar field potentials, with ensuing unnatural fine tuning conditions for underlying particle physics theories. We derive constraints on parameter space from bounds location first few peaks troughs cosmic microwave radiation (CMBR) power...
We consider the generalized Chaplygin gas (GCG) proposal for unification of dark energy and matter show that it admits an unique decomposition into components once phantom-like is excluded. Within this framework, we study structure formation difficulties associated to unphysical oscillations or blow-up in power spectrum can be circumvented. Furthermore, dominance related time when density fluctuations start deviating from linear $δ\sim a$ behaviour.
The thawing quintessence model with a nearly flat potential provides natural mechanism to produce an equation of state parameter, $w$, close $\ensuremath{-}1$ today. We examine the behavior such models for case in which satisfies slow-roll conditions: $[(1/V)(dV/d\ensuremath{\phi}){]}^{2}\ensuremath{\ll}1$ and $(1/V)({d}^{2}V/d{\ensuremath{\phi}}^{2})\ensuremath{\ll}1$, we derive analog approximation both matter scalar field contribute density. show that this limit, all converge unique...
We use the most recent Type Ia supernova data in order to study dark energy–dark matter (XCDM) unification approach context of generalized Chaplygin gas (GCG) model. Rather surprisingly, we find that allow models with α > 1. have studied how GCG adjusts flat and non-flat models, our results show is consistent a case up 68 per cent confidence level. Actually this holds even if one relaxes prior assumption. also analysed what should expect from future experiment such as Supernova/Acceleration...
Knowing the late time evolution of Universe and finding out causes for this are important challenges modern cosmology. In work, we adopt a model-independent cosmographic approach approximate Hubble parameter considering Pade approximation which works better than standard Taylor series $z>1$. With this, constrain low-redshift observations coming from SNIa, BAO, $H(z)$, $H_{0}$ , strong-lensing time-delay as well Megamaser angular diameter distances. We confirm tensions with $\Lambda$CDM model...
We consider a low redshift ($z<0.7$) cosmological data set comprising megamasers, cosmic chronometers, type Ia supernovae and baryon acoustic oscillations, which we bin according to their redshift. For each bin, read the value of ${H}_{0}$ by fitting directly flat $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. Doing so, find that descends with redshift, allowing one fit line nonzero slope statistical significance $2.1\ensuremath{\sigma}$. Our analysis rests on use chronometers break...
ABSTRACT In view of the recent measurement H0 from Hubble Space Telescope and Supernova for Equation State (SH0ES) team, we explore possibility existence a negative cosmological constant [anti-de Sitter (AdS) vacua in dark energy sector] Universe. this regard, consider quintessence fields on top compare such construction with Λ cold matter (ΛCDM) model using different combination cosmic microwave background, Type Ia supernova, baryon acoustic oscillation, data. Various comparison estimators...
$\Lambda$CDM tensions are by definition model dependent; one sees anomalies through the prism of $\Lambda$CDM. Thus, progress towards tension resolution necessitates checking consistency to localise missing physics either in redshift or scale. Since Universe is dynamical and a proxy for time, it imperative first perform checks involving redshift, then scale, as next steps settle ``systematics versus new physics" debate foster informed building. We present review hierarchy assumptions...
In this work we have investigated the possibility of having a late time accelerated phase universe, suggested by recent supernova observation, in context Brans Dicke (BD) theory with symmetry breaking potential and matter field. We find that perfect fluid field (pressureless pressure) cannot support acceleration but dissipative pressure can drive acceleration. also calculated some cosmological parameters our model to match observations.
ABSTRACT Hubble constant H0 and weighted amplitude of matter fluctuations S8 determinations are biased to higher lower values, respectively, in the late universe with respect early values inferred by Planck collaboration within flat ΛCDM cosmology. If these anomalies physical, that is, not due systematics, they naively suggest decreases increases effective redshift. Here, subjecting density today Ωm a prior, corresponding combination CMB BAO data, we perform consistency test Planck-ΛCDM...
In the Randall-Sundrum (RS) II braneworld scenario, general relativity (GR) is modified by adding an extra dimension such that it indistinguishable from GR in weak gravity limit. However, modifications may leave a mark strong field regime. We therefore analyze massive scalar perturbations around rotating black holes RS model. Unlike GR, these carry tidal charge contains information about spatial dimension, and rotation parameter for can exceed unity. Through method of continued fractions, we...
The generalized Chaplygin gas is characterized by the equation of state $p=\ensuremath{-}A/{\ensuremath{\rho}}^{\ensuremath{\alpha}}$, with $\ensuremath{\alpha}>\ensuremath{-}1$ and $w>\ensuremath{-}1$. We generalize this model to allow for cases where $\ensuremath{\alpha}<\ensuremath{-}1$ or $w<\ensuremath{-}1$. This generalization leads three new versions gas: an early phantom in which $w\ensuremath{\ll}\ensuremath{-}1$ at times asymptotically approaches $w=\ensuremath{-}1$...
We consider cosmological inflation driven by the rolling tachyon in context of braneworld scenario. show that sufficient consistent with observational constraints can be achieved for well defined upper limits on five-dimensional mass scale, string scale and coupling bosonic string.