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Anirudh Pradhan

Publications and source records attributed to Anirudh Pradhan.

At least 163 records · Page 9Linked to original sources
arXiv2011

LRS Bianchi Type-II Massive String Cosmological Models in General Relativity

The present study deals with locally rotationally symmetric (LRS) Bianchi type II cosmological models representing massive string. The energy-momentum tensor for such string as formulated by Letelier (1983) is used to construct massive string cosmological models for which we assume that the expansion ($θ$) in the models is proportional to the shear ($σ$). This condition leads to $A = B^{m}$, where A and B are the metric coefficients and m is constant. We have derived two types of models depending on different values of m i.e. for $m\neq \sqrt{2}$ and $m = \sqrt{2}$ respectively. For suitable choice of constant m (i.e. for $m = 1/2$), it is observed that in early stage of the evolution of the universe, the universe is dominated by strings in both cases. Our models are in accelerating phase which is consistent to the recent observations of type Is supernovae. Some physical and geometric behaviour of the models are also discussed.

physics.gen-ph↗
arXiv2011

An Interacting Two-Fluid Scenario for Dark Energy in FRW Universe

We study the evolution of the dark energy parameter within the scope of a spatially flat and isotropic Friedmann-Robertson-Walker (FRW) model filled with barotropic fluid and dark energy. To obtain the deterministic solution we choose the scale factor $a(t) = \sqrt{t e^{t}}$ which yields a time dependent deceleration parameter (DP). In doing so we consider the case minimally coupled with dark energy to the perfect fluid as well as direct interaction with it.

gr-qc↗
arXiv2010

Is Hubble's Expansion due to Dark Energy

{\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 $Λ$. In the present paper, it is shown that `the formula for acceleration due to dark-energy' is (almost) exactly of same-form as `the acceleration formula from the Hubble's law'. Hence, it is concluded that: yes, `indeed it is the dark-energy responsible for the Hubble's expansion too, in-addition to the current on-going acceleration of the universe'.

physics.gen-ph↗
arXiv2010

Dark Energy Model in Anisotropic Bianchi Type-III Space-Time with Variable EoS Parameter

A new dark energy model in anisotropic Bianchi type-III space-time with variable equation of state (EoS) parameter has been investigated in the present paper. To get the deterministic model, we consider that the expansion $θ$ in the model is proportional to the eigen value $σ^{2}_{~2}$ of the shear tensor $σ^{j}_~i$. The EoS parameter $ω$ is found to be time dependent and its existing range for this model is in good agreement with the recent observations of SNe Ia data (Knop et al. 2003) and SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. 2004). It has been suggested that the dark energy that explains the observed accelerating expansion of the universe may arise due to the contribution to the vacuum energy of the EoS in a time dependent background. Some physical aspects of dark energy model are also discussed.

physics.gen-ph↗
arXiv2010

Bianchi Type-II String Cosmological Models in Normal Gauge for Lyra's Manifold with Constant Deceleration Parameter

The present study deals with a spatially homogeneous and anisotropic Bianchi-II cosmological models representing massive strings in normal gauge for Lyra's manifold by applying the variation law for generalized Hubble's parameter that yields a constant value of deceleration parameter. The variation law for Hubble's parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential form. Using these two forms, Einstein's modified field equations are solved separately that correspond to expanding singular and non-singular models of the universe respectively. The energy-momentum tensor for such string as formulated by Letelier (1983) is used to construct massive string cosmological models for which we assume that the expansion ($θ$) in the model is proportional to the component $σ^{1}_{~1}$ of the shear tensor $σ^{j}_{i}$. This condition leads to $A = (BC)^{m}$, where A, B and C are the metric coefficients and m is proportionality constant. Our models are in accelerating phase which is consistent to the recent observations. It has been found that the displacement vector $β$ behaves like cosmological term $Λ$ in the normal gauge treatment and the solutions are consistent with recent observations of SNe Ia. It has been found that massive strings dominate in the decelerating universe whereas strings dominate in the accelerating universe. Some physical and geometric behaviour of these models are also discussed.

physics.gen-ph↗
arXiv2010

Bianchi Type-I Anisotropic Dark Energy Models with Constant Deceleration Parameter

New dark energy models in anisotropic Bianchi type-I (B-I) space-time with variable EoS parameter and constant deceleration parameter have been investigated in the present paper. The Einstein's field equations have been solved by applying a variation law for generalized Hubble's parameter in B-I space-time. The variation law for Hubble's parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential form. Using these two forms, Einstein's field equations are solved separately that correspond to expanding singular and non-singular models of the universe respectively. The equation of state (EoS) parameter $ω$ is found to be time dependent and its existing range for this model is in good agreement with the recent observations of SNe Ia data, SNe Ia data (with CMBR anisotropy) and galaxy clustering statistics. The cosmological constant $Λ$ is found to be a decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations.

physics.gen-ph↗
arXiv2010

A theoretically-explained new-variant of Modified-Newtonian-Dynamics (MOND)

It is surprising that we hardly know only 5% of the universe. Rest of the universe is made up of 70% of dark-energy and 25% of dark-matter. Dark-energy is responsible for acceleration of the expanding universe; whereas dark-matter is said to be necessary as extra-mass of bizarre-properties to explain the anomalous rotational-velocity of galaxy. Though the existence of dark-energy has gradually been accepted in scientific community, but the candidates for dark-matter have not been found as yet and are too crazy to be accepted. Thus, it is obvious to look for an alternative theory in place of dark-matter. Israel-scientist M. Milgrom has suggested a 'Modified Newtonian Dynamics (MOND)' which appears to be highly successful for explaining the anomalous rotational-velocity. But unfortunately MOND lacks theoretical support. The MOND, in-fact, is (empirical) modification of Newtonian-Dynamics through modification in the kinematical acceleration term 'a' (which is normally taken as $a=\frac{v^{2}}{r}$) as effective kinematic acceleration $a_{effective} = a μ(\frac{a}{a_{0}})$, wherein the $μ$-function is 1 for usual-values of accelerations but equals to $\frac{a}{a_{0}} (\ll 1)$ if the acceleration 'a' is extremely-low lower than a critical value $a_0 (10^{-10} m/s^{2})$. In the present paper, a novel variant of MOND is proposed with theoretical backing; wherein with the consideration of universe's acceleration $a_{d}$ due to dark-energy, a new type of $μ$-function on theoretical-basis emerges out leading to $a_{effective} = a(1 - K \frac{a_{0}}{a})$. The proposed theoretical-MOND model too is able to fairly explain qualitatively the more-or-less 'flat' velocity-curve of galaxy-rotation, and is also able to predict a dip (minimum) on the curve.

physics.gen-ph↗
arXiv2010

Redefining Heat and Work in the Right Perspective of Second-law-of-Thermodynamics

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' and `Relativity' are interlinked.

physics.gen-ph↗
arXiv2010

A Novel Concept for Mass as Complex-Mass towards Wave-particle Duality

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'

physics.gen-ph↗
arXiv2009

`Zero-spin-photon hypothesis' finds another important application: Could possibly solve the `infinity-problem' of QED without the need of renormalization

`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.

physics.gen-ph↗
arXiv2009

Genesis of Dark Energy: Dark Energy as Consequence of Release and Two-stage Tracking Cosmological Nuclear Energy

Recent observations on Type-Ia supernovae and low density ($Ω_{m} = 0.3$) measurement of matter including dark matter suggest that the present-day universe consists mainly of repulsive-gravity type `exotic matter' with negative-pressure often said `dark energy' ($Ω_{x} = 0.7$). But the nature of dark energy is mysterious and its puzzling questions, such as why, how, where and when about the dark energy, are intriguing. In the present paper the authors attempt to answer these questions while making an effort to reveal the genesis of dark energy and suggest that `the cosmological nuclear binding energy liberated during primordial nucleo-synthesis remains trapped for a long time and then is released free which manifests itself as dark energy in the universe'. It is also explained why for dark energy the parameter $w = - {2/3}$. Noting that $ w = 1$ for stiff matter and $w = {1/3}$ for radiation; $w = - {2/3}$ is for dark energy because $"-1"$ is due to `deficiency of stiff-nuclear-matter' and that this binding energy is ultimately released as `radiation' contributing $"+ {1/3}"$, making $w = -1 + {1/3} = - {2/3}$. When dark energy is released free at $Z = 80$, $w = -{2/3}$. But as on present day at $Z = 0$ when radiation strength has diminished to $δ\to 0$, $w = -1 + δ{1/3} = - 1$. This, thus almost solves the dark-energy mystery of negative pressure and repulsive-gravity. The proposed theory makes several estimates /predictions which agree reasonably well with the astrophysical constraints and observations. Though there are many candidate-theories, the proposed model of this paper presents an entirely new approach (cosmological nuclear energy) as a possible candidate for dark energy.

physics.gen-ph↗
arXiv2009

Zero-spin-photon hypothesis: `Zero-spin-photon generation in pair-production and its subsequent decay into neutrino and antineutrino' - solves many-riddles of physics and universe

`What is work and what is heat' is re-investigated from the perspective of second law of thermodynamics. It is shown that the inevitable consequence of second law of thermodynamics and spin conservation necessitates the possible generation of zero spin photon in pair production process, and its subsequent decay explains the birth of neutrino and antineutrino. The proposed neutrino-genesis, solves many riddles of physics and universe. The riddles considered and explained are about: (i) mysterious neutrino (and antineutrino) and its bizarre properties such as handed-ness and parity-violation, (ii) questionable asymmetry/ excess of matter over antimatter, (iii) possibility of existence of antimatter world and (iv) parity (P) violation and aspects of CP and CPT violation or restoration in the universe.

physics.gen-ph↗
arXiv2008

Inhomogeneous Perfect Fluid Universe with Electromagnetic Field in Lyra Geometry

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 $θ$ in the model is proportional to the shear $σ$. It has been found that the solutions are consistent with the recent observations of type Ia supernovae and the displacement vector $β(t)$ affects entropy. Physical and geometric aspects of the models are also discussed in presence and absence of magnetic field.

gr-qc↗
arXiv2008

Tilted Bianchi Type V Bulk Viscous Cosmological Models with Varying $Λ$-Term

Conformally flat tilted Bianchi type V cosmological models in presence of a bulk viscous fluid and heat flow are investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density. The cosmological constant is found to be a decreasing function of time, which is supported by results from recent type Ia supernovae observations. Some physical and geometric aspects of the models are also discussed.

gr-qc↗
arXiv2008

Magnetized String Cosmological Model in Cylindrically Symmetric Inhomogeneous Universe with Variable Cosmological-Term $Λ$

Cylindrically symmetric inhomogeneous magnetized string cosmological model is investigated with cosmological term $Λ$ varying with time. To get the deterministic solution, it has been assumed that the expansion ($θ$) in the model is proportional to the eigenvalue $σ^{1}_{1}$ of the shear tensor $σ^{i}_{j}$. The value of cosmological constant for the model is found to be small and positive which is supported by the results from recent supernovae Ia observations. The physical and geometric properties of the model are also discussed in presence and absence of magnetic field.

gr-qc↗
arXiv2008

Inhomogeneous Bulk Viscous Fluid Universe with Electromagnetic Field and Variable $Λ$-Term

Cylindrically symmetric inhomogeneous cosmological model for bulk viscous fluid distribution with electromagnetic field is obtained. The source of the magnetic field is due to an electric current produced along the z-axis. $F_{12}$ is the non-vanishing component of electromagnetic field tensor. To get the deterministic solution, it has been assumed that the expansion $θ$ in the model is proportional to the shear $σ$. The values of cosmological constant for these models are found to be small and positive at late time, which are consistent with the results from recent supernovae Ia observations. Physical and geometric aspects of the models are also discussed in presence and absence of magnetic field.

gr-qc↗
arXiv2008

Magnetized Bianchi Type $VI_{0}$ Barotropic Massive String Universe with Decaying Vacuum Energy Density $Λ$

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 ($θ$) in the model is proportional to the shear ($σ$) and also the fluid obeys the barotropic equation of state. It was found that vacuum energy density $Λ\propto \frac{1}{t^{2}}$ 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.

gr-qc↗