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...

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...

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.

In this work it is shown that the Brans-Dicke theory of gravity does not always go over to general relativity in $\ensuremath{\omega}\ensuremath{\rightarrow}\ensuremath{\alpha}$ limit. It also shown, by an order magnitude estimate, one can get as a limit when $\ensuremath{\omega}\ensuremath{\rightarrow}\ensuremath{\alpha},$ only if trace energy-momentum tensor describing all fields other than scalar field nonzero.

Recent cosmological observations reveal that we are living in a flat accelerated expanding universe. In this work have investigated the nature of potential compatible with power law expansion universe self interacting Brans Dicke cosmology perfect fluid background and analyzed whether supports expansion. It is found positive relevant scenario can drive for negative coupling parameter $\omega$. The evolution density perturbation also scenerio seen model allows growing modes

We have investigated the possibility of having a late time accelerated expansion phase for universe. used dissipative fluid in Brans-Dicke(BD) theory this purpose. The model does not involve any potential BD scalar field. obtained best fit values different parameters our by comparing predictions with SNIa data and also from ultra-compact radio sources.

We have investigated the cosmological scenarios with a four-dimensional effective action which is connected multidimensional, supergravity and string theories. The solution for scale factor such that initially universe undergoes decelerated expansion but in late times it enters into accelerated phase. In fact, asymptotically becomes de Sitter universe. dilaton field our model decreasing function of time constant resulting exit from scalar–tensor theory to standard Einstein's gravity. Also...

We consider different classes of scalar field models including quintessence and tachyon fields with a variety generic potentials belonging to the thawing type. focus on observational quantities like Hubble parameter, luminosity distance as well related Baryon Acoustic Oscillation measurement. Our study shows that present state observations, one cannot distinguish amongst various which in turn be distinguished from cosmological constant. analysis indicates there is small chance observe dark...

In this work, we have studied the observational constraints on Cardassian model for dark energy. We compared with existing supernova data. The dependence of locations cosmic microwave background radiation (CMBR) peaks parameters also been studied. find, in particular, that data from Archeops location first peak and BOOMERANG third peak, together data, significantly constrain parameter space.

We consider bulk antisymmetric tensor fields of various ranks in a Randall-Sundrum scenario. show that, rank 2 onwards, the zero-modes projections these on $(3+1)$-dimensional visible brane become increasingly weaker as increases. All such 4 or more are absent from dynamics four dimensions. This leaves only zero-mode graviton to have coupling $\ensuremath{\sim}1/{M}_{P}$ with matter, thus explaining why large-scale behavior universe is governed by gravity only. also computed masses heavier...

We have considered the most general gauge invariant five-dimensional action of a second rank antisymmetric Kalb-Ramond tensor theory, including topological term form ${ϵ}^{ABLMN}{B}_{AB}{H}_{LMN}$ in Randall-Sundrum scenario. Such field ${B}_{AB}$ (whose rank-3 strength is ${H}_{LMN}$), which appears massless sector heterotic string assumed to coexist with gravity bulk. The third corresponding has well-known geometric interpretation as space-time torsion. only nontrivial classical solutions...

Non-canonical scaling of the form $ρ_{x} \propto ρ_{m} a^ξ$, where $ρ_{x}$ and $ρ_{m}$ are energy densities dark matter, respectively, provides a natural way to address coincidence problem -why two comparable today. This non-canonical is achieved by suitable interaction between components. We study observational constraints imposed on such models from cosmic microwave background (CMB) anisotropy spectrum. Using recent WMAP results for location CMB peaks, we determine admissible parameter...

Previous analysis of AstroSat observations the black hole system MAXI J1535-571, have revealed presence a strong Quasi-Periodic Oscillation (QPO) whose frequency is correlated with high energy spectral index. Here, we fit spectra as emitted from truncated disc an inner hot corona, study QPO dependence on other parameters and model dependent r.m.s time-lag to identify physical variation are responsible for QPO. The found also correlate scattering fraction (i.e. soft photons Comptonized) its...

We consider a string-inspired torsion-dilaton-gravity action in Randall-Sundrum braneworld scenario and show that, an effective four-dimensional theory on the visible brane, rank-2 antisymmetric Kalb-Ramond field (source of torsion) is exponentially suppressed. The result similar to our earlier [B. Mukhopadhyaya, S. Sen, SenGupta, Phys. Rev. Lett. 89, 121101 (2002); 259902(E) (2002)], where no dilaton was present bulk. This offers explanation apparent invisibility torsion space-time....

We study the linear growth function f for large scale structures in a cosmological scenario where Generalised Chaplygin Gas (GCG) serves as dark energy candidate. parametrize index parameter of redshift and do comparative between theoretical rate proposed parametrization. Moreover, we demonstrate that rates wide range models can be modeled accurately by our Finally, compile data set consisting 28 points within (0.15,3.8) to constrain rate. It includes direct from various projects/surveys...

ABSTRACT Black hole X-ray binaries routinely exhibit quasi-periodic oscillations (QPOs) in their power density spectrum. Studies of QPOs have demonstrated immense ability to understand these dynamical systems although unambiguous origin still remains a challenge. We investigate the energy-dependent properties Type-C detected for H 1743-322 as observed with AstroSat its two outbursts 2016 and 2017. The combined broad-band LAXPC SXT spectrum is well modelled soft thermal hard Comptonization...

We have investigated the constraints on Cardassian model using recent results from Wilkinson Microwave Anisotropy Probe (WMAP) for locations of peaks Cosmic Background (CMB) anistropy spectrum. find that is consistent with observational data certain range parameter $n$ and cosmological parameters. favoured compared to $\Lambda$CDM model, a higher spectral index ($n_s \approx 1$) together lower value Hubble $h$ ($h\leq 0.71$). But smaller values $n_s$, both are equally favoured. Also,...

ABSTRACT We present the spectro-timing analysis of black hole binary system GX 339−4 using AstroSat data extracted at beginning outbursts in 2017 and 2019. The joint spectral fitting Large Area X-ray Proportional Counter (LAXPC) Soft Telescope (SXT) revealed that source was a faint low/hard state for both 2019 observations, with nearly equal photon indexes ∼1.57 ∼1.58 Eddington ratios, L/LEdd, 0.0011 0.0046, respectively. addition reflection component into modelling improved fit (Δχ2 ≈ 6 Δχ2...

While the dynamical origin of variability observed in Galactic Black hole systems, such as quasi-periodic oscillations (QPOs), are still a matter debate, insight into radiative components responsible for behaviour can be obtained by studying their energy dependent temporal behaviour. In particular, one needs to ascertain which variations parameters best fit time-averaged spectral reproduce fractional r.m.s and time-lags. However, obtain meaningful interpretation, standard component have...

Abstract We present a spectro-timing analysis of the black hole X-ray transient GX 339–4 using simultaneous observations from AstroSat and Neutron Star Interior Composition Explorer (NICER) during 2021 outburst period. The combined spectrum obtained NICER, Large Area Proportional Counter SXT data is effectively described by model comprising thermal disk component, hard Comptonization reflection component with an edge . Our NICER spectra indicates source to be in low/hard state, photon index...

4U 1543-47 underwent its brightest outburst in 2021 after two decades of inactivity. During decay phase, AstroSat conducted nine observations the source spanning from July $1^{st}$ to September $26^{th}$, 2021. The first three were performed with an offset 40 arcmin AstroSat/LAXPC, while remaining six on-axis observations. In this report, we present a comprehensive spectral analysis as it was High/Soft state during entire observation period. exhibited disk-dominated spectra weak high-energy...

This work investigates the nature of potential function $V(\ensuremath{\varphi})$ relevant to power law inflation in a minimally coupled scalar field cosmology along with perfect or causal viscous fluid. It is observed that if coefficient viscosity proportional square root density fluid, required an exponential \ensuremath{\varphi}.