arXiv subjects

Utpal Mukhopadhyay

Publications and source records attributed to Utpal Mukhopadhyay.

22 records · Page 2Linked 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

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.

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