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Rahaman F.,Jadavpur University | Mukhopadhyay U.,Satyabharati Vidyapith | Sarkar R.,Future Campus School
International Journal of Theoretical Physics | Year: 2011

We present a model for the present accelerating Universe and focus on the different important physical variables involved in the model under the phenomenological assumption Λ∝H2 with a prescription for equation of state parameter in the form, where ω0 and ω1 are two constants and τ is a parameter having dimension of time t2. General expressions for the density parameter Ω and deceleration parameter q are obtained which under specific bound reproduce some of the previous results. We explore physical features of these parameters which (i) provide the scenario of complete evolution of the cosmos with ω(t) and (ii) agree mostly with the observational status of the present phase of the accelerating Universe. © 2011 Springer Science+Business Media, LLC.

Mukhopadhyay U.,Satyabharati Vidyapith | Rahaman F.,Jadavpur University
International Journal of Modern Physics D | Year: 2010

Two phenomenological variable Λ models, viz. Λ ∼ (/a)2 and Λ ∼ ρ, have been studied under the assumption that the equation of state parameter ω is a function of time. The selected Λ models are found to be equivalent both in four and five dimensions. The possibility of signature flip of the deceleration parameter is also shown. © 2010 World Scientific Publishing Company.

Mukhopadhyay U.,Satyabharati Vidyapith | Rahaman F.,Jadavpur University | Sarkar R.,Jadavpur University
International Journal of Theoretical Physics | Year: 2013

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 well as accelerating. Here, the presence of dark energy has been established by including a time-dependent Λ term in the Einstein's field equations. This model is compatible with the idea of an accelerating Universe so far as the value of the deceleration parameter is concerned. Possibility of a change in sign of the deceleration parameter is also discussed. The impact of considering the speed of light as variable in the field equations has also been investigated by using a well known time-dependent Λ model. © 2013 Springer Science+Business Media New York.

Biswas S.N.,Mahatma Aswini Kumar Dutta Road | Mukhopadhyay U.,Satyabharati Vidyapith
European Physical Journal H | Year: 2014

In the present paper we have presented some documents to reveal the longstanding relationship of Indian amateur astronomer R.G. Chandra with the British Astronomical Association and American Association of Variable Star Observers. © EDP Sciences, Springer-Verlag.

Ghosh P.P.,A.J.C. Bose Polytechnic | Usmani A.A.,Aligarh Muslim University | Mukhopadhyay U.,Satyabharati Vidyapith
Astrophysics and Space Science | Year: 2013

The concept of oscillatory Universe appears to be realistic and buried in the dynamic dark energy equation of state. We explore its evolutionary history under the framework of general relativity. We observe that oscillations do not go unnoticed with such an equation of state and that their effects persist later on in cosmic evolution. The 'classical' general relativity seems to retain the past history of oscillatory Universe in the form of increasing scale factor as the classical thermodynamics retains this history in the form of increasing cosmological entropy. © 2013 Springer Science+Business Media Dordrecht.

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