Papers by Anirudh Pradhan
We present cosmological models with variable cosmological term (Λ) in the context of higher-dimen... more We present cosmological models with variable cosmological term (Λ) in the context of higher-dimensional spacetime. It has been observed that in these models particle horizon exists and the cosmological term is decaying with time. Further, it is shown that the new models solve entropy problem and generate several models obtained in four-dimensional spacetime.
There are some misnomers and misconceptions about what is heat and what is work; the recognition ... more There are some misnomers and misconceptions about what is heat and what is work; the recognition of heat and work is even more difficult when it comes to categorize energy as heat or work. Since both heat and work are energy the name-confusion does not make much difference from engineering point of view, but re-defining `heat' and `work' in the right-perspective of second-law-of-thermodynamics \cite {ref1} is necessary to revise our understanding at fundamental level. It is concluded that `heat is the energy carried by mass-less \textit{photons} whereas work is energy carried by mass-ive material \textit{fermions}'. Revised understanding of heat and work in this way has far reaching consequences in Physics [2-4]. The present paper lays emphasis on re-defining heat and work, removing the prevailing misconception, talks about single photon interaction and heat property of photon. Also, interestingly, it is noted that different fields of study such as `Thermodynamics' a...
In this paper the observational consequence of the cosmological models and the expression for the... more In this paper the observational consequence of the cosmological models and the expression for the neoclassical tests, luminosity distance, angular diameter distance and look back time are analyzed in the framework of Lyra geometry. It is interesting to note that the space time of the universe is not only free of Big Bang singularity but also exhibits acceleration during its evolution.
Bianchi type V bulk viscous fluid cosmological models are investigated with dynamic cosmological ... more Bianchi type V bulk viscous fluid cosmological models are investigated with dynamic cosmological term $\Lambda(t)$. Using a generation technique (Camci {\it et al.}, 2001), it is shown that the Einstein's field equations are solvable for any arbitrary cosmic scale function. Solutions for particular forms of cosmic scale functions are also obtained. The cosmological constant is found to be decreasing function of time, which is supported by results from recent type Ia supernovae observations. Some physical and geometrical aspects of the models are also discussed.
Romanian Journal of Physics
A new class of cylindrically symmetric inhomogeneous string cosmological models is investigated. ... more A new class of cylindrically symmetric inhomogeneous string cosmological models is investigated. To get the deterministic solution, it has been assumed that the expansion ($\theta$) in the model is proportional to the eigen value $\sigma^{1}_{1}$ of the shear tensor $\sigma^{i}_{j}$. The physical and geometric aspects of the model are also discussed. Comment: 14 pages
An LRS Bianchi type-V cosmological models representing a viscous fluid distribution with a time d... more An LRS Bianchi type-V cosmological models representing a viscous fluid distribution with a time dependent cosmological term $\Lambda$ is investigated. To get a determinate solution, the viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density. It turns out that the cosmological term $\Lambda(t)$ is a decreasing function of time, which is consistent with recent observations of type Ia supernovae. Various physical and kinematic features of these models have also been explored.
Cylindrically symmetric inhomogeneous string cosmological model of the universe in presence of el... more Cylindrically symmetric inhomogeneous string cosmological model of the universe in presence of electromagnetic field is investigated. We have assumed that F_{12} is the only non-vanishing component of electromagnetic field tensor F_{ij}. The Maxwell's equations show that F_{12} is the function of $x$ alone whereas the magnetic permeability is the function of x and t both. To get the deterministic solution, it has been assumed that the expansion ($\theta$) in the model is proportional to the eigen value $\sigma^{1}_{1}$ of the shear tensor $\sigma^{i}_{j}$. Some physical and geometric prperties of the model are also discussed. Comment: 12 pages, no figure. Submitted to Rom. Rep. Phys
Cylindrically symmetric inhomogeneous string cosmological models in presence of electromagnetic f... more Cylindrically symmetric inhomogeneous string cosmological models in presence of electromagnetic field is investigated. We have assumed that $F_{12}$ is the only non-vanishing component of $F_{ij}$. The Maxwell's equations show that $F_{12}$ is the function of $x$ alone whereas the magnetic permeability is the function of $x$ and $t$ both. To get the deterministic solution, it has been assumed that the expansion ($\theta$) in the model is proportional to the eigen value $\sigma^{1}_{1}$ of the shear tensor $\sigma^{i}_{j}$. The physical and geometric aspects of the model are also discussed.
A new class of cylindrically symmetric inhomogeneous cosmological models for perfect fluid distri... more A new class of cylindrically symmetric inhomogeneous cosmological models for perfect fluid distribution with electromagnetic field is obtained in the context of Lyra's geometry. We have obtained two types of solutions by considering the uniform as well as time dependent displacement field. The source of the magnetic field is due to an electric current produced along the z-axis. Only $F_{12}$ is a non-vanishing component of electromagnetic field tensor. To get the deterministic solution, it has been assumed that the expansion $\theta$ in the model is proportional to the shear $\sigma$. It has been found that the solutions are consistent with the recent observations of type Ia supernovae and the displacement vector $\beta(t)$ affects entropy. Physical and geometric aspects of the models are also discussed in presence and absence of magnetic field. Comment: 22 pages, no figure, minor corrections
Bianchi type $VI_{0}$ massive string cosmological models using the technique given by Letelier (1... more Bianchi type $VI_{0}$ massive string cosmological models using the technique given by Letelier (1983) with magnetic field are investigated. To get the deterministic models, we assume that the expansion ($\theta$) in the model is proportional to the shear ($\sigma$) and also the fluid obeys the barotropic equation of state. It was found that vacuum energy density $\Lambda \propto \frac{1}{t^{2}}$ which matches with natural units. The behaviour of the models from physical and geometrical aspects in presence and absence of magnetic field is also discussed.
In the present paper a new concept is introduced that: `mass is a complex quantity'. The conc... more In the present paper a new concept is introduced that: `mass is a complex quantity'. The concept of complex-mass suggests that the total mass M of a moving body is complex sum of: (i) the real-part (grain or rest) mass $m_{g}$ establishing its particle behaviour and (ii) the imaginary-part mass $m_{p}$ governing its wave properties. Mathematically, the complex mass $M = m_{g} + im_{p}$; the magnitude $\mid M \mid = (m_{g}^{2} + m_{p}^{2})^{{1/2}}. The theory proposed here explains successfully several effects such as `Compton effect' and `refraction of light' which could not be explained otherwise by a single theory of wave or particle. Also explained are `Doppler effect for light', `photo-electric effect', `Uncertainty principle', `Relativity' and `supersymmetry'
Romanian Journal of Physics
A new class of cylindrically symmetric inhomogeneous string cosmological models in presence of el... more A new class of cylindrically symmetric inhomogeneous string cosmological models in presence of electromagnetic field is investigated. We have assumed that F 12 is the only non-vanishing component of F ij . The Maxwell's equations show that F 12 is the function of x alone whereas the magnetic permeability is the function of x and t both. Also, the Einstein field equations have been solved with string source in which magnetic field are absent. The physical and geometric aspects of the model in presence and absence of magnetic field are also discussed.
{\it The universe is expanding} is known (through Galaxy observations) since 1929 through Hubble&... more {\it The universe is expanding} is known (through Galaxy observations) since 1929 through Hubble's discovery ($V = H D$). Recently in 1999, it is found (through Supernovae observations) that the universe is not simply expanding but is accelerating too. We, however, hardly know only $4\%$ of the universe. The Wilkinson Microwave Anisotropy Probe (WMAP) satellite observational data suggest $73\%$ content of the universe in the form of dark-energy, $23\%$ in the form of non-baryonic dark-matter and the rest $4\%$ in the form of the usual baryonic matter. The acceleration of the universe is ascribed to this dark-energy with bizarre properties (repulsive-gravity). The question is that whether Hubble's expansion is just due to the shock of big-bang & inflation or it is due to the repulsive-gravity of dark-energy? Now, it is believed to be due to dark-energy, say, by re-introducing the once-discarded cosmological-constant $\Lambda$. In the present paper, it is shown that `the formu...
`Zero-spin-photon hypothesis' as proposed in an earlier paper [1] states that: `due to inevit... more `Zero-spin-photon hypothesis' as proposed in an earlier paper [1] states that: `due to inevitable consequence of the second-law of thermodynamics and spin-conservation, the `zero-spin-photon' is generated in pair-production process (of elementary particles), which decays into neutrino and antineutrino'. The zero-spin photon hypothesis explains [1] several riddles of physics and universe. In the present paper, it is shown that `the zero-spin photon hypothesis' when incorporated into the higer-order Feynman diagram (with a closed-loop) could possibly solve the half-a-century-old and famous `infinity-problem' of QED, and thus could avoid the need of the so called `re-normalization' procedure. Comment: 14 pages, 7 figures, This paper suggests a possible-way to eliminate infinity-problem of QED without renormalization
A new class of LRS Bianchi type ${\rm VI}_{0}$ cosmological models with free gravitational fields... more A new class of LRS Bianchi type ${\rm VI}_{0}$ cosmological models with free gravitational fields and a variable cosmological term is investigated in presence of perfect fluid as well as bulk viscous fluid. To get the deterministic solution we have imposed the two different conditions over the free gravitational fields. In first case we consider the free gravitational field as magnetic type whereas in second case `gravitational wrench' of unit `pitch" is supposed to be present in free gravitational field. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density. The cosmological constant $\Lambda$ is found to be a decreasing function of time and positive which is corroborated by results from recent supernovae Ia observations. The physical and geometric aspects of the models are discussed.
Two new cylindrically symmetric inhomogeneous string cosmological models are investigated in pres... more Two new cylindrically symmetric inhomogeneous string cosmological models are investigated in presence of magnetic field. We have assumed that F 12 is the only non-vanishing component of electromagnetic field tensor F ij . The Maxwell's equations show that F 12 is the function of x alone whereas the magnetic permeability ¯ μ is the function of x and t both. To get the deterministic solution, it has been assumed that the metric coefficients are separable in the form as A = f (x)(t), B = g(x)k(t), C = g(x)ν(t). Also, the Einstein field equations have been solved with string source in which magnetic field is absent. Some physical and geometric aspects of the models in presence and absence of magnetic field are discussed.
Many of the general-relativity-tests such as bending of light near a star and gravitational red/b... more Many of the general-relativity-tests such as bending of light near a star and gravitational red/blue shift are explained without general-relativity & without Newtonian-approach. The authors first cast doubts on both, the Newtonian and the relativistic approach; and proposes a novel alternative-explanation. The new alternative explanation is based on refraction-phenomenon of optics. Estimation of results, with new approach, are in agreement with known values. Though physics is different, but it is argued that general-relativity based gravitational-bending and refraction-based bending have more in common than is generally realized. Also discussed are black-hole and gravitational-lensing in the new perspective of refraction. The new refraction-based theory makes a few new predictions and also suggests a few tests.. Comment: 16 pages, 3 figures, 22 references
Romanian Journal of Physics
A plane-symmetric magnetized inhomogeneous cosmological model of perfect fluid distribution with ... more A plane-symmetric magnetized inhomogeneous cosmological model of perfect fluid distribution with variable magnetic permeability is investigated. The source of the magnetic field is due to an electric current produced along the z-axis. Thus F 12 is the only non-vanishing component of electromagnetic field tensor F ij . To get a unique determined solution, we assume the free gravitational field is Petrov type-II non-degenerate. For our derived model we obtain the deceleration parameter q = −1 as in the case of de Sitter universe. Some physical and geometric properties of the model are also discussed.
Romanian Journal of Physics
The physical behavior of cosmological solutions to Einstein's field equations for a spatially hom... more The physical behavior of cosmological solutions to Einstein's field equations for a spatially homogeneous and anisotropic Bianchi type-I space-time have been investigated by taking into account the affect of time varying cosmological parameters viz., gravitational constant (G), cosmological constant (Λ) and deceleration parameter (q) in scalar-tensor theory of gravitation proposed by Sáez and Ballester (Phys. Lett. A 113:467, 1986). The concept of time dependent deceleration parameter with some proper assumption yields the average scale factor a(t) = (sinh(αt))
Indian Journal of Physics
Exact solutions of Einstein’s field equations are obtained in a spatially homogeneous and anisotr... more Exact solutions of Einstein’s field equations are obtained in a spatially homogeneous and anisotropic Bianchi type-I space-time in presence of a dissipative fluid with constant and time dependent cosmological term $\Uplambda$ Λ . Einstein’s field equations are solved by considering a time dependent deceleration parameter, which affords a late time acceleration in the universe. The cosmological constant $\Uplambda$ Λ is found to be a decreasing function of time and it approaches a small positive value at present epoch, which is corroborated by consequences from recent supernovae I a observations. To get the deterministic solution a barotropic equation of state together with shear viscosity, proportional to expansion scalar, is also assumed. It is observed that initial nature of singularity is not changed due to presence of viscous fluid. The basic equation of thermodynamics is deduced and thermodynamic aspects of models are discussed. Physical and geometric properties of cosmological...
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Papers by Anirudh Pradhan