Time variable $\Lambda$ and the accelerating Universe (2008)
Mukhopadhyay, U., Ray, Saibal, Usmani, A. A.
We perform a deductive study of accelerating Universe and focus on the importance of variable time-dependent $\Lambda$ in the Einstein's field equations under the phenomenological assumption,...
Electromagnetic mass model admitting conformal motion (2008)
Ray, Saibal, Usmani, A A, Rahaman, F, Kalam, M, Chakraborty, K
We study charged fluid spheres under the 4-dimensional Einstein-Maxwell space-time. The solutions thus obtained admitting conformal motion. We also investigate whether the solutions set provide...
Galactic rotation curves and brane world models (2008)
Rahaman, F., Kalam, M., DeBenedictis, A., Usmani, A. A., Ray, Saibal
In the present investigation flat rotational curves of the galaxies are considered under the framework of brane-world models where the 4d effective Einstein equation has extra terms which arise from...
Generalized Model for $\Lambda$-Dark Energy (2008)
Mukhopadhyay, Utpal, Ray, P. C., Ray, Saibal, Choudhury, S. B. Datta
Einstein field equations under spherically symmetric space-times are considered here in connection to dark energy investigation. A set of solutions are obtained for a kinematical $\Lambda$ model,...
The dark energy equation of state (2008)
Usmani, A. A., Ghosh, P. P., Mukhopadhyay, Utpal, Ray, P. C., Ray, Saibal
We perform a study of cosmic evolution with an equation of state parameter $\omega(t)=\omega_0+\omega_1(t\dot H/H)$ by selecting a phenomenological $\Lambda$ model of the form, $\dot\Lambda\sim H^3$....
Dark Energy Models With Variable Equation Of State Parameter (2007)
Mukhopadhyay, Utpal, Ray, Saibal, Choudhury, S. B. Dutta
Two variable $\Lambda$ models, viz. $\Lambda \sim (\dot a/a)^2$ and $\Lambda \sim \rho$ have been studied under the assumption that the equation of state parameter $\omega$ is a function of time. The...
Mukhopadhyay, Utpal, Ghosh, Partha Pratim, Khlopov, Maxim, Ray, Saibal
Among various phenomenological $\Lambda$ models, a time-dependent model $\dot \Lambda\sim H^3$ is selected here to investigate the $\Lambda$-CDM cosmology. Using this model the expressions for the...
Scenario of inflationary cosmology from the phenomenological $\Lambda$ models (2007)
Ray, Saibal, Ray, P. C., Ghosh, Partha Pratim, Mukhopadhyay, Utpal, Chowdhury, Partha
Choosing the three phenomenological models of the dynamical cosmological term $\Lambda$, viz., $\Lambda \sim (\dot a/a)^2$, $\Lambda \sim {\ddot a/a}$ and $\Lambda \sim \rho$ where $a$ is the cosmic...
$\Lambda$-CDM Universe: A Phenomenological Approach With Many Possibilities (2007)
Mukhopadhyay, U., Ray, Saibal, Choudhury, S. B. Dutta
A time-dependent phenomenological model of $\Lambda$, viz. $\dot \Lambda\sim H^3$ is selected to investigate the $\Lambda$-CDM cosmology. Time-dependent form of the equation of state parameter...
Do Solar system tests permit higher dimensional general relativity? (2007)
Rahaman, F., Ray, Saibal, Kalam, M., Sarker, M.
We perform a survey whether higher dimensional Schwarzschild space-time is compatible with some of the solar system phenomena. As a test we examine five well known solar system effects, viz., (1)...
Periodicity of ~155 days in solar electron fluence (2007)
Chowdhury, Partha, Ray, P. C., Ray, Saibal
In this paper we have investigated the occurrence rate of high energetic(E>10 MeV) solar electron flares measured by IMP-8 spacecraft of NASA for solar cycle 21 (June, 1976 to August, 1986) first...
Ray, Saibal, Das, Basanti, Rahaman, Farook, Ray, Subharthi
In this article, Einstein-Maxwell space-time has been considered in connection to some of the astrophysical solutions as previously obtained by Tolman (1939) and Bayin (1978). The effect of inclusion...
Large Number Hypothesis: A Review (2007)
Ray, Saibal, Mukhopadhyay, Utpal, Ghosh, Partha Pratim
Large dimensionless numbers, arising out of ratios of various physical constants, intrigued many scientists, especially Dirac. Relying on the coincidence of large numbers, Dirac arrived at the...
Scenarios of cosmic string with variable cosmological constant (2006)
Ray, Saibal, Rahaman, Farook, Mukhopadhyay, Utpal
Exact solutions of the Einstein field equations with cosmic string and space varying cosmological constant, viz., $\Lambda= \Lambda(r)$, in the energy-momentum tensors are presented. Three cases have...
Electromagnetic Mass in $(n+2)$ Dimensional Space-times (2005)
Einstein-Maxwell field equations correspoding to higher dimensional description of static spherically symmetric space-time have been solved under two specific set of conditions, viz., (i) $\rho \ne...
Relativistic Electromagnetic Mass Models: Charged Dust Distribution in Higher Dimensions (2005)
Ray, Saibal, Bhadra, Sumana, Mohanti, G.
Electromagnetic mass models are proved to exist in higher dimensional theory of general relativity corresponding to charged dust distribution. Along with the general proof a specific example is also...
Dark energy models with time-dependent gravitational constant (2005)
Ray, Saibal, Mukhopadhyay, Utpal
Two phenomenological models of $\Lambda$, viz. $\Lambda \sim (\dot a/a)^2$ and $\Lambda \sim \ddot a/a$ are studied under the assumption that $G$ is a time-variable parameter. Both models show that...
Dark energy with polytropic equation of state (2005)
Mukhopadhyay, Utpal, Ray, Saibal
Equation of state parameter plays a significant role for guessing the real nature of dark energy. In the present paper polytropic equation of state $p=\omega\rho^n$ is chosen for some of the...
The Dynamic Cosmological Term $\Lambda$: Some Aspects of Phenomenological Models (2005)
Mukhopadhyay, Utpal, Ray, Saibal
Choosing a phenomenological model of $\Lambda$, viz. $\Lambda \sim \dot H$, it has been shown that this model of $\Lambda$ is equivalent to other three types of $\Lambda$, $\Lambda \sim (\dot...
Dark Matter and Dark Energy: a Scenario of Accelerating Universe (2005)
Mukhopadhyay, Utpal, Ray, Saibal
Dark matter, the major component of the matter content of the Universe, played a significant role at early stages during structure formation. But at present the Universe is dark energy dominated as...
Lorentz's electromagnetic mass: a clue for unification? (2004)
We review in the present article the conjecture of electromagnetic mass by Lorentz. The philosophical perspectives and historical accounts of this idea are described, especially, in the light of...
Searching for a Solution to the Age Problem of the Universe (2004)
Ray, Saibal, Mukhopadhyay, Utpal
We present here a phenomenological cosmological model under perfect fluid distribution with a stiff equation of state $p=\rho$. The erstwhile cosmological constant is assumed to be a time dependent...
Relativistic Gravitational mass in Tolman-VI type solution (2004)
Some known solutions for static charged fluid spheres of Tolman-VI type in general relativity are reexamined. The gravitational mass that appears in the Pant and Sah \cite{pan79} and Tikekar...
Accelerating Universe with a dynamic cosmological term (2004)
Ray, Saibal, Mukhopadhyay, Utpal, Meng, Xin-He
Keeping in mind the current picture of an accelerating and flat Universe, some specific dynamical models of the cosmological term $\Lambda$ have been selected for investigating the nature of dark...
Tolman-Bayin type static charged fluid spheres in general relativity (2004)
In a static spherically symmetric Einstein-Maxwell spacetime the class of astrophysical solution found out by Ray and Das (2002) and Pant and Sah (1979) are revisited here in connection to the...
Relativistic anisotropic charged fluid spheres with varying cosmological constant (2003)
Ray, Saibal, Bhadra, Sumana, Sengupta, Anand S.
Static spherically symmetric anisotropic source has been studied for the Einstein-Maxwell field equations assuming the erstwhile cosmological constant $ \Lambda $ to be a space-variable scalar, viz.,...
Energy density in general relativity: a possible role for cosmological constant (2002)
We consider a static spherically symmetric charged anisotropic fluid source of finite physical radius (\sim 10^{-16} cm) by introducing a scalar variable \Lambda dependent on the radial coordinate r...
Experimental result regarding the maximum limit of the radius of the electron \sim 10^{-16} cm and a few of the theoretical works suggest that the gravitational mass which is a priori a positive...