G P SINGH
Articles written in Pramana – Journal of Physics
Volume 11 Issue 2 August 1978 pp 119-134 Solids
Propagation of longitudinal ultrasonic waves in RbH2PO4 near its ferroelectric phase transition temperature
Ferroelectric phase transition in RbH2PO4 has been investigated using propagation of longitudinal acoustic waves along the polar axis near the transition temperature. The velocity of this mode is continuous across the transition temperature. Velocity data in the ferroelectric phase are analyzed in terms of coupled soft modeacoustic mode model of Pytte to obtain the temperature dependence of the soft mode frequency. The attenuation data in the ferroelectric phase show power law dependence. It follows scaling behaviour of the type predicted by Kawasaki from the mode-mode coupling theory and the dynamical scaling.
Volume 45 Issue 2 August 1995 pp 189-193
Static models of cosmic strings in general relativity
Exact solutions to Einstein’s equations for a cloud of massive strings with a general static metric representing spherical plane and hyperbolic symmetries are derived. Some properties of massive strings for different cases are also discussed.
Volume 49 Issue 2 August 1997 pp 205-212 Research Articles
A new class of cosmological models in Lyra geometry
FRW models have been studied in the cosmological theory based on Lyra’s geometry. A new class of exact solutions has been obtained by considering a time dependent displacement field for constant deceleration parameter models of the universe.
Volume 52 Issue 2 February 1999 pp 121-126
Gravitational energy in Brans-Dicke cosmological models
The behaviour of gravitational energy and scalar field during the evolution of the universe within the framework of Brans-Dicke theory has been discussed. With help of the Landau-Lifshitz pseudo-tensor for the flat Friedmann-Robertson-Walker model, it is found that (i) the total energy of the universe is always zero, (ii) the Brans-Dicke scalar field for all Ω >-0 contributes energy to the negative energy of gravitational field and this gets transferred to the vacuum energy which accelerates the expansion of the universe.
Volume 54 Issue 5 May 2000 pp 729-736 Research Articles
Particle production in higher derivative theory
G P Singh A Beesham R V Deshpande
The effect of particle production on the evolution of the spatially flat Friedmann-Lemaitre-Robertson-Walker cosmological model during the early stages of the universe is analysed in the framework of higher derivative theory. The universe has been considered as an open thermodynamic system where particle production gives rise to a supplementary negative creation pressure in addition to the thermodynamic pressure. The dynamical behaviour of both exponential as well as power law solutions have been discussed.
Volume 94 All articles Published: 13 October 2020 Article ID 0147 Research Article
Some Bianchi I dark energy models in Brans–Dicke theory
G P SINGH ASHWINI R LALKE NIKHIL HULKE
The present article deals with the study of interacting and non-interacting dark energy (DE) and dark matter (DM) in the spatially homogeneous and anisotropic Bianchi I space–time within the framework of Brans–Dicke (BD) scalar–tensor theory of gravitation. As the set of field equations is not closed, exact solutions are obtained using power-law relation and assuming a linearly varying deceleration parameter. The physical acceptability and stability of the obtained model are scrutinised using energy conditions and squared speed of sound. The statefinder diagnostic method is adopted to discuss and measure the deviation of the considered model from the $\Lambda$ cold dark matter ($\Lambda$CDM) model.
Volume 97, 2023
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