arXiv subjects

Anirudh Pradhan

Publications and source records attributed to Anirudh Pradhan.

At least 127 records · Page 7Linked to original sources

arXiv2019

Analytical model of dark energy stars

In this article we study the structure and stability of compact astrophysical objects which are ruled by the dark energy equation of state (EoS). The existence of dark energy is important for explaining the current accelerated expansion of the universe. Exact solutions to Einstein field equations (EFE) have been found by considering particularized metric potential, Finch and Skea ansatz \cite{Finch}. The obtained solutions are relevant to the explanation of compact fluid sphere. Further, we have observed at the junction interface, the interior solution is matched with the Schwarzschild's exterior vacuum solution. Based on that, we have noticed the obtained solutions are well in agreement with the observed maximum mass bound of $\approx$ 2$M_{\bigodot}$, namely, PSR J1416-2230, Vela X-1, 4U 1608-52, Her X-1 and PSR J1903+327, whose predictable masses and radii are not compatible with the standard neutron star models. Also, the stability of the stellar configuration has been discussed briefly, by considering the energy conditions, surface redshift, compactness, mass-radius relation in terms of the state parameter ($ω$). Finally, we demonstrate that the features so obtained are physically acceptable and consistent with the observed/reported data \citep{Gondek-Rosinska,Glendenning}. Thus, the present dark energy equation of state appears talented regarding the presence of several exotic astrophysical matters.

gr-qc↗

arXiv2019

Traversable Wormholes in $f(R,T)$ Gravity

In the present article, models of traversable wormholes within the $f(R, T)$ modified gravity theory are investigated. We have presented some wormhole models, developed from various hypothesis for the substance of their matter, i.e. various relationships with their components of pressure (lateral and radial). The solutions found for the shape functions of the wormholes produced complies with the required metric conditions. The suitability of solution is examined by exploring null, strong and dominant energy conditions. It is surmised that the normal matter in the throat may pursue the energy conditions yet the gravitational field exuding from the adjusted gravity hypothesis support the appearance of the non-standard geometries of wormholes.

physics.gen-ph↗

arXiv2019

Two Fluid Scenario in Bianchi Type-I Universe

In this paper, we study a Bianchi type -I model of universe filled with barotropic and dark energy(DE) type fluids. The present values of cosmological parameters such as Hubble constant $H_0$, barotropic, DE and anisotropy energy parameters $(Ω_{m})_0$, $(Ω_{de})_0$ and $(Ω_σ)_0 $ and Equation of State(EoS) parameter for DE ($ω_{de}$) are statistically estimated in two ways by taking 38 point data set of Hubble parameter H(z) and 581 point data set of distance modulus of supernovae in the range $0\leq z \leq 1.414$. It is found that the results agree with the Planck result [P.A.R. Ade, et al., Astron. Astrophys. 594 A14 (2016)] and more latest result obtained by Amirhashchi and Amirhashchi [H. Amirhashchi and S. Amirhashchi, arXiv:1811.05400v4 (2019)]. Various physical properties such as age of the universe, deceleration parameter etc have also been investigated.

gr-qc↗

arXiv2019

A Dark Energy Quintessence Model of the Universe

In this paper, we have presented a model of the FLRW universe filled with matter and dark energy fluids, by assuming an ansatz that deceleration parameter is a linear function of the Hubble constant. This results in a time-dependent DP having decelerating-accelerating transition phase of the universe. This is a quintessence model $ω_{(de)}\geq -1$. The quintessence phase remains for the period $(0 \leq z \leq 0.5806)$. The model is shown to satisfy current observational constraints. Various cosmological parameters relating to the history of the universe have been investigated.

gr-qc↗

arXiv2019

FRW dark energy cosmological model with hybrid expansion law

In this work, we study a cosmological model of spatially homogeneous and isotropic accelerating universe which exhibits a transition from deceleration to acceleration. For this, Friedmann Robertson Walker(FRW) metric is taken and Hybrid expansion law $a(t)=t^α \exp(βt )$ is proposed and derived. We consider the universe to be filled with two types of fluids barotropic and dark energy which have variable equations of state. The evolution of dark energy, Hubble, and deceleration parameters etc., have been described in the form of tables and figures. We consider $581$ data's of observed values of distance modulus of various SNe Ia type supernovae from union $2.1$ compilation to compare our theoretical results with observations and found that model satisfies current observational constraints. We have also calculated the time and redshift at which acceleration in the Universe had commenced.

gr-qc↗

arXiv2019

Anisotropic bulk viscous string cosmological models of the Universe under a time-dependent deceleration parameter

We investigate a new class of LRS Bianchi type-II cosmological models by revisiting in the paper of Mishra {\it et al} (2013) by considering a new deceleration parameter (DP) depending on the time in string cosmology for the modified gravity theory suggested by S$\acute{a}$ez \& Ballester (1986). We have considered the energy-momentum tensor proposed by Leteliar (1983) for bulk viscous and perfect fluid under some assumptions. To make our models consistent with recent astronomical observations, we have used scale factor (Sharma {\it et al} 2018; Garg {\it et al} 2019) $ a(t)=\exp{[\frac{1}β\sqrt{2 βt + k}]}$, where $β$ and $k$ are positive constants and it provides a time-varying DP. By using the recent constraints ($H_{0}=73.8$, and $q_{0} = -0.54$) from SN Ia data in combination with BAO and CMB observations (Giostri {\it et al}, arXiv:1203.3213v2[astro-ph.CO]), we affirm $β= 0.0062$ and $k = 0.000016$. For these constraints, we have substantiated a new class of cosmological transit models for which the expansion takes place from early decelerated phase to the current accelerated phase. Also, we have studied some physical, kinematic and geometric behavior of the models, and have found them consistent with observations and well established theoretical results . We have also compared our present results with those of Mishra {\it et al} (2013) and observed that the results in this paper are much better, stable under perturbation and in good agreement with cosmological reflections.

physics.gen-ph↗

arXiv2019

FLRW accelerating universe with interactive dark energy

We have developed an accelerating cosmological model for the present universe which is phantom for the period $ (0 \leq z \leq 1.99)$ and quintessence phase for $(1.99 \leq z \leq 2.0315)$. The universe is assumed to be filled with barotropic and dark energy(DE) perfect fluid in which DE interact with matter. For a deceleration parameter(DP) having decelerating-accelerating transition phase of universe, we assume hybrid expansion law for scale factor. The transition red shift for the model is obtained as $z_t = 0.956$. The model satisfies current observational constraints.

gr-qc↗

arXiv2017

Bianchi type-I Dust Filled Accelerating Brans- Dicke Cosmology

In this paper, spatially homogeneous and anisotropic Bianchi type-I cosmological models of Brans-Dicke theory of gravitation are investigated. The model represents accelerating universe at present and is considered to be dominated by dark energy. Cosmological constant $Λ$ is considered as a candidate for the dark energy that has negative pressure and is responsible for the present acceleration. The derived model agrees at par with the recent SN Ia observations. We have set BD-coupling constant $ω$ to be ~$40000$, ~seeing the solar system tests and evidences. We have discussed the various physical and geometrical properties of the models and have compared them with the corresponding relativistic models.

physics.gen-ph↗

arXiv2017

The BIonic diode in a system of trigonal manifolds

A BIonic diode is constructed of two polygonal manifolds connected by a Chern-Simons manifold. The shape and the angle between atoms of molecules on the boundary of two polygonal manifolds are completely different. For this reason, electrons on the Chern-Simons manifold are repelled by molecules at the boundary of one manifold and absorbed by molecules on the boundary of another manifold. The attractive and repulsive forces between electrons are carried by masive photons. For example, when two non-similar trigonal manifolds join to each other, one non-symmetrical hexagonal manifold is emerged and the exchanged photons form Chern-Simons fields which live on a Chern-Simons manifold in a BIon. While, for a hexagonal manifold, with similar trigonal manifolds, the photons exchanged between two trigonal manifolds cancel the effect of each other and BIonic energy becomes zero. Also, exchanging photons between heptagonal and pentagonal manifolds lead to the motion of electrons on the Chern-Simons manifold and formation of BIonic diode. The mass of photons depend on the shape of molecules on the boundary of manifolds and the length of BIon in a gap between two manifolds.

physics.gen-ph↗

arXiv2017

Quarkonium in a thermal BIon

In the present article, the authors intend to propose a new theory which potentially allows the propagation of the formation and the evolution of quarkonium in a thermal BIon. When quarks are close to each other, quarkonium behaves like a scalar and by their getting away, it transits to a fermionic system. In order to analyze this particular behaviour, a new outlook approach needs to be adopted as the concurrent view is found deficient to analyse the aforesaid behaviour. Therefore, the authors' post deliberation accept the fermions and fermionic being cognate. We need to accept a theory that the origin of fermions and bosons be the same. However, in $M$-theory, these particles are independent and for this reason, \textbf{we use a new broader theory based on Lie-$N$-Algebra and we call it BLNA (Broad Lie-$N$-Algebra)} theory. Thus, the BLNA in a way the $M$-theory with $11$ dimensions. In this model, two types of energies with opposite signs emerge from nothing such as the sum over them becomes zero. They produce two types of branes with opposite quantum numbers and bosonic fields, which interact with each other and get compact. By compacting branes, the quarks and anti-quarks are produced on branes and exchange the graviton and the gravitino. These particles produce two types of wormholes which act opposite to each other. They preclude from closing or getting away of branes from each other and also occurrence of confinement. This confined potential which emerges from these wormholes depends on the separation distance between quarks and anti-quarks and also on temperature of system and is reduced to predicted potential in experiments and QCD. Also, total entropy of this system grows with increasing temperature and produces a repulsive force which leads to the separation of quarks and anti-quarks and also to the emergence of deconfinement.

hep-th↗

arXiv2017

On the origin of generalized uncertainty principle from compactified M5-brane

In this paper, we demonstrate that compactification in M-theory can lead to a deformation of field theory consistent with the generalized uncertainty principle (GUP).We observe that the matter fields in the M3-brane action contain higher derivative terms. We demonstrate that such terms can also be constructed from a reformulation of the field theory by the GUP. In fact, we will construct the Heisenberg algebra consistent with this deformation, and explicitly demonstrate it to be the Heisenberg algebra obtained from the GUP. Thus, we use compactification in M-theory to motivate for the existence of the GUP.

gr-qc↗

arXiv2017

Birth of the GUP and its effect on the entropy of the Universe in Lie-$N$-algebra

In this paper, the origin of the generalized uncertainty principle (GUP) in an $M$-dimensional theory with Lie-$N$-algebra is considered. This theory which we name GLNA(Generalized Lie-$N$-Algebra)-theory can be reduced to $M$-theory with $M=11$ and $N=3$. In this theory, at the beginning, two energies with positive and negative signs are created from nothing and produce two types of branes with opposite quantum numbers and different numbers of timing dimensions. Coincidence with the birth of these branes, various derivatives of bosonic fields emerge in the action of the system which produce the $r$ GUP for bosons. These branes interact with each other, compact and various derivatives of spinor fields appear in the action of the system which leads to the creation of the GUP for fermions. The previous predicted entropy of branes in the GUP is corrected as due to the emergence of higher orders of derivatives and different number of timing dimensions.

physics.gen-ph↗

arXiv2016

Cosmological expansion and contraction from Pauli exclusion principle in $M0$-branes

We show that the Pauli exclusion principle in a system of $M0$-branes can give rise to the expansion and contraction of the universe which is located on an $M3$-brane. We start with a system of $M0$-branes with high symmetry, which join mutually and form pairs of $M1$-anti-$M1$-branes. The resulting symmetry breaking creates gauge fields that live on the $M1$-branes and play the role of graviton tensor modes, which induce an attractive force between the $M1$ and anti-$M1$ branes. Consequently, the gauge fields that live on the $M1$-branes, and the scalar fields which are attached symmetrically to all parts of these branes, decay to fermions that attach anti-symmetrically to the upper and lower parts of the branes, and hence the Pauli exclusion principle emerges. By closing $M1$-branes mutually, the curvatures produced by parallel spins will be different from the curvatures produced by anti-parallel spins, and this leads to an inequality between the number of degrees of freedom on the boundary surface and the number of degrees of freedom in the bulk region. This behavior is inherited in the $M3$-brane on which the universe is located, and hence this leads to the emergence of the universe expansion and contraction. In this sense, the Pauli exclusion principle rules the cosmic dynamics.

gr-qc↗

arXiv2016

Teleparallel loop quantum cosmology in a system of intersecting branes

Recently, some authors have removed the big bang singularity in teleparallel Loop Quantum Cosmology (LQC) and have shown that the universe may undergo a number of oscillations. We investigate the origin of this type of teleparallel theory in a system of intersecting branes in M-theory in which the angle between them changes with time. This system is constructed by two intersecting anti-D8-branes, one compacted D4-brane and the other a D3-brane. These branes are built by joining M0-branes which develop in decaying fundamental strings. The compacted D4-brane is located between two intersecting anti-D8 branes and glues to one of them. Our universe is located on the D3 brane which wraps the D4 brane from one end and sticks to one of the anti-D8 branes from another one. In this system, there are three types of fields, corresponding to compacted D4 branes, intersecting branes and D3-branes. These fields interact with each other and make the angle between branes oscillate. By decreasing this angle and approaching the intersecting anti-D8 branes towards each other, the D4 brane rolls, the D3 brane wraps around the D4 brane, and t he universe contracts. By separating the intersecting branes and increasing the angle, the D4 brane rolls in the opposite direction, the D3 brane separates from it and the expansion branch begins. Also, the interaction between branes in this system gives us the exact form of the relevant Lagrangian for teleparallel LQC.

gr-qc↗

arXiv2016

Emergence and oscillation of cosmic space by joining M1-branes

Recently, it has been proposed by Padmanabhan that the difference between the number of degrees of freedom on the boundary surface and the number of degrees of freedom in a bulk region leads to the expansion of the universe. Now, a natural question arises, how this model could explain the oscillation of universe between contraction and expansion branches? We try to address this issue in the framework of BIonic system. In this model, $M0$-branes join to each other and give rise to a pair of $M1$-anti-$M1$-branes. The fields which live on these branes play the roles of massive gravitons that cause the emergence of a wormhole between them and formation of a BIon system. This wormhole dissolves into M1-branes and causes a divergence between the number of degrees of freedom on the boundary surface of $M1$ and the bulk leading to an expansion of $M1$-branes. When $M1$-branes become close to each other, the square energy of their system becomes negative and some tachyonic states emerge. To removes these states, $M1$-branes compact, the sign of compacted gravity changes, causing the arising of anti-gravity: in this case, branes get away from each other. By articulating $M1$-BIons, an M3-brane and an anti-$M3$-brane are created and connected by three wormholes forming an $M3$-BIon. This new system behaves like the initial system and by closing branes to each other, they compact and, by getting away from each other, they open. Our universe is located on one of these M3-branes and, by compacting $M3$-brane, it contracts and, by opening it, it expands.

gr-qc↗

arXiv2016

The evolution of Brown-York quasilocal energy due to evolution of Lovelock gravity in a system of M0-branes

Recently, it has been suggested in [JHEP 12(2015)003] that the Brown-York mechanism can be used to measure the quasilocal energy in Lovelock gravity. We have used this method in a system of M0-branes and show that the Brown-York energy evolves in the process of birth and growth of Lovelock gravity. This can help us to predict phenomenological events which are emerged as due to dynamical structure of Lovelock gravity in our universe. In this model, first, M0-branes join to each other and form an M3-brane and an anti-M3-branes connected by an M2-brane. This system is named BIon. Universes and anti-universes live on M3-branes and M2 plays the role of wormhole between them. By passing time, M2 dissolves in M3's and nonlinear massive gravities, like Lovelock massive gravity, emerges and grows. By closing M3-branes, BIon evolves and wormhole between branes makes a transition to black hole. During this stage, Brown-York energy increases and shrinks to large values at the colliding points of branes. By approaching M3-branes towards each other, the square energy of their system becomes negative and some tachyonic states are produced. To remove these states, M3-branes compact, the sign of compacted gravity changes, anti-gravity is created which leads to getting away of branes from each other. Also, the Lovelock gravity disappears and it's energy forms a new M2 between M3-branes. By getting away of branes from each other, Brown-York energy decreases and shrinks to zero.

hep-th↗

arXiv2015

Refraction-Based Alternative Explanation for: Bending of Light Near a Star, Gravitational Red/Blue Shift and Black-Hole

In this research-paper, many of the general-relativity-tests such as bending of light near a star and gravitational red/blue shift are explained without general-relativity & even without Newtonian-approach. The authors first raise questions on the validity of both, the Newtonian and the relativistic approach; and then propose 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.

physics.gen-ph↗

arXiv2015

Bianchi type-I transit cosmological models with time dependent gravitational and cosmological constants - reexamined

The present study reexamines the recent work of Pradhan et al. (Indian J. Phys. 88: 757, 2014) and obtained general exact solutions of the Einstein's field equations with variable gravitational and cosmological "constants" for a spatially homogeneous and anisotropic Bianchi type-I space-time. To study the transit behaviour of Universe, we consider a law of variation of scale factor $a(t) = \left(t^{k} e^{t}\right)^{\frac{1}{n}}$ which yields a time dependent deceleration parameter $q = - 1 + \frac{nk}{(k + t)^{2}}$, comprising a class of models that depicts a transition of the universe from the early decelerated phase to the recent accelerating phase. We find that the time dependent deceleration parameter is reasonable for the present day Universe and give an appropriate description of the evolution of the universe. For $n = 0.27k$, we obtain $q_{0} = -0.73$ which is similar to observed value of deceleration parameter at present epoch. It is also observed that for $n \geq 2$ and $k = 1$, we obtain a class of transit models of the universe from early decelerating to present accelerating phase. For $k = 0$, the universe has non-singular origin. In these models, we arrive at the decision that, from the structure of the field equations, the behaviour of cosmological and gravitational constants and are related. Taking into consideration the observational data, we conclude that the cosmological constant behaves as a positive decreasing function of time whereas gravitational constant is increasing and tend to a constant value at late time. $H(z)/(1+z)$ data ($32$ points) and model prediction as a function of redshift for different $k$ and $n$ are successfully presented by using recent data (Farooq and Ratra, Astrophys. J. 66: L7, 2013). Some physical and geometric properties of the models are also discussed.

physics.gen-ph↗