Satyabharati Vidyapith

North Guwāhāti, India

Satyabharati Vidyapith

North Guwāhāti, India

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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 | Usmani A.A.,Aligarh Muslim University | Ghosh P.P.,A. J. C. Bose Polytechnic
International Journal of Theoretical Physics | Year: 2011

We perform a deductive study of accelerating Universe and focus on the importance of variable time-dependent Λ in the Einstein's field equations under the phenomenological assumption, Λ=αH2 for the full physical range of α. The relevance of variable Λ with regard to various key issues like dark matter, dark energy, geometry of the field, age of the Universe, deceleration parameter and barotropic equation of state has been trivially addressed. The deceleration parameter and the barotropic equation of state parameter obey a straight line relationship for a flat Universe described by Friedmann and Raychaudhuri equations. Both the parameters are found identical for α=1. © 2010 Springer Science+Business Media, LLC.


Mukhopadhyay U.,Satyabharati Vidyapith | Ghosh P.P.,A.J.C. Bose Polytechnic
International Journal of Theoretical Physics | Year: 2010

Two phenomenological models of Λ, viz. and 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 model corresponds to a repulsive situation and hence correlates with the present status of the accelerating Universe. The other model 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. © 2010 Springer Science+Business Media, LLC.


Khlopov M.,National Research Nuclear University MEPhI | Ghosh P.P.,A.J.C. Bose Polytechnic | Mukhopadhyay U.,Satyabharati Vidyapith
International Journal of Theoretical Physics | Year: 2011

Among various phenomenological Λ models, a time-dependent model Ȧ~H3 is selected here to investigate the Λ-CDM cosmology. The model can follow from dynamics, underlying the origin of Λ. Using this model the expressions for the time-dependent equation of state parameter ω and other physical parameters are derived. It is shown that in H3 model accelerated expansion of the Universe takes place at negative energy density, but with a positive pressure. It has also been possible to obtain the change of sign of the deceleration parameter q during cosmic evolution. © 2010 Springer Science+Business Media, LLC.


Ghosh P.P.,A. J. C. Bose Polytechnic | Mukhopadhyay U.,Satyabharati Vidyapith
Astrophysics and Space Science | Year: 2012

We investigate the possible variation of c in the context of the present accelerating Universe as discovered through SN Ia observations and show that variability of c is not permitted under the variable Λ models. © 2011 Springer Science+Business Media B.V.


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.


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.


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.


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.


Mukhopadhyay U.,Satyabharati Vidyapith | Chakraborty I.,Adamas Institute of Technology | Usmani A.A.,Aligarh Muslim University
International Journal of Theoretical Physics | Year: 2015

We study a dynamic Λ model with varying gravitational constant G under the Kaluza-Klein cosmology. Physical features and the limitations of the present model have been explored and discussed. Solutions are found mostly in accordance with the observed features of the accelerating universe. Interestingly, signature flipping of the deceleration parameter is noticed and the present age of the Universe is also attainable under certain stringent conditions. We find that the time variation of gravitational constant is not permitted without vintage Λ. © 2015 Springer Science+Business Media New York

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