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Saibal Ray

Publications and source records attributed to Saibal Ray.

172 records · Page 10Linked to original sources
arXiv2006

Searching for a Solution to the Age Problem of the Universe

We present here a phenomenological cosmological model under perfect fluid distribution with a stiff equation of state $p=ρ$. The erstwhile cosmological constant is assumed to be a time dependent variable, i.e., $Λ= Λ(t)$ in our study. It has been shown that the estimates of different cosmological parameters from this model are in good agreement with the experimental results, especially 13.79 Gyr as the age of the universe is quite satisfactory. The behavior and relation of $Λ$-stiff fluid model with dust, viscous fluid and variable $G$ have also been investigated in detail.

astro-ph↗
arXiv2005

Electromagnetic Mass in $(n+2)$ Dimensional Space-times

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) $ρ\ne 0$, $ν^\prime= 0$ and (ii) $ρ=0$, $ ν^\prime\ne 0$ where $ρ$ and $ν$ represent the mass density and metric potential. The solution sets thus obtained satisfy the criteria of being electromagnetic mass model such that the gravitational mass vanishes for the vanishing charge density $σ$ and also the space-time becomes flat. Physical features related to other parameters also have been discussed.

gr-qc↗
arXiv2005

Classical Electron Model with Negative Energy Density in Einstein-Cartan Theory of Gravitation

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 quantity in Newtonian mechanics may become negative in general theory of relativity. It is argued that such a negative gravitational mass and hence negative energy density also can be obtained with a better physical interpretation in the framework of Einstein-Cartan theory.

gr-qc↗
arXiv2005

The Dynamic Cosmological Term $Λ$: Some Aspects of Phenomenological Models

Choosing a phenomenological model of $Λ$, viz. $Λ\sim \dot H$, it has been shown that this model of $Λ$ is equivalent to other three types of $Λ$, $Λ\sim (\dot a/a)^2$, $Λ\sim \ddot a/a$ and $Λ\sim ρ$. Through an indirect approach, it has also been possible to put a limit on the deceleration parameter $q$. It has been shown that if $q$ becomes less than -1, then this model can predict about the presence of phantom energy.

astro-ph↗
arXiv2005

Dark energy with polytropic equation of state

Equation of state parameter plays a significant role for guessing the real nature of dark energy. In the present paper polytropic equation of state $p=ωρ^n$ is chosen for some of the kinematical $Λ$-models viz., $Λ\sim (\dot a/a)^2$, $Λ\sim \ddot a/a$ and $Λ\sim ρ$. Although in dust cases ($ω=0$) closed form solutions show no dependency on the polytropic index $n$, but in non-dust situations some new possibilities are opened up including phantom energy with supernegative ($ω<-1$) equation of state parameter.

astro-ph↗
arXiv2005

Dark energy models with time-dependent gravitational constant

Two phenomenological models of $Λ$, viz. $Λ\sim (\dot a/a)^2$ and $Λ\sim \ddot a/a$ are studied under the assumption that $G$ is a time-variable parameter. Both models show that $G$ is inversely proportional to time as suggested earlier by others including Dirac. The models considered here can be matched with observational results by properly tuning the parameters of the models. Our analysis shows that $Λ\sim \ddot a/a$ model corresponds to a repulsive situation and hence correlates with the present status of the accelerating Universe. The other model $Λ\sim (\dot a/a)^2$ is, in general, attractive in nature. Moreover, it is seen that due to the combined effect of time-variable $Λ$ and $G$ the Universe evolved with acceleration as well as deceleration. This later one indicates a Big Crunch.

astro-ph↗
arXiv2005

Energy density in general relativity: a possible role for cosmological constant

We consider a static spherically symmetric charged anisotropic fluid source of finite physical radius (\sim 10^{-16} cm) by introducing a scalar variable Λdependent on the radial coordinate r under general relativity. From the solution sets a possible role of the cosmological constant is investigated which indicates the dependency of energy density of electron on the variable Λ.

gr-qc↗
arXiv2004

Tolman-Bayin type static charged fluid spheres in general relativity

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 phenomenological relationship between the gravitational and electromagnetic fields. It is qualitatively shown that the charged relativistic stars of Tolman (1939) and Bayin (1978) type are of purely electromagnetic origin. The existence of this type of astrophysical solutions is a probable extension of Lorentz's conjecture that electron-like extended charged particle possesses only `electromagnetic mass' and no `material mass'.

astro-ph↗
arXiv2003

Relativistic anisotropic charged fluid spheres with varying cosmological constant

Static spherically symmetric anisotropic source has been studied for the Einstein-Maxwell field equations assuming the erstwhile cosmological constant $ Λ$ to be a space-variable scalar, viz., $ Λ= Λ(r) $. Two cases have been examined out of which one reduces to isotropic sphere. The solutions thus obtained are shown to be electromagnetic in origin as a particular case. It is also shown that the generally used pure charge condition, viz., $ ρ+ p_r = 0 $ is not always required for constructing electromagnetic mass models.

gr-qc↗