Papers by Aragam Prasanna
Physical Review D, 2002
Spin 1 2 particles in geodesic trajectories experience no gravitational potential but they still ... more Spin 1 2 particles in geodesic trajectories experience no gravitational potential but they still have non-zero couplings to the curvature tensor. The effect of space time curvature on fermions can be parameterized by a vector and a pseudo-vector potential. These apparent CP T violating terms can be measured with satellite based spinpolarized torsion balance and clock comparison experiments. The Earth's curvature effect is of the order of 10 −37 Gev which is not far from the present bounds of ∼ 10 −29 Gev on such CP T violating couplings.
Nuclear Physics B, 1998
We derive the wave equation obeyed by electromagnetic fields in curved spacetime. We find that th... more We derive the wave equation obeyed by electromagnetic fields in curved spacetime. We find that there are Riemann and Ricci curvature coupling terms to the photon polarisation which result in a polarisation dependent deviation of the photon trajectories from null geodesics. Photons are found to have an effective mass in an external gravitational field and their velocity in an inertial frame is in general less than c. A physically relevant consequence of the analysis is that the curvature corrections to the propagation of electromagnetic radiation (in a homogenous and isotropic spacetime) keep the velocities subluminal provided the strong energy condition is satisfied. We further show that the claims of superluminal velocities in higher derivative gravity theories are erroneous and arise due to the neglect of Riemann and Ricci coupling terms in the wave equation, of Einstein gravity.
Nuclear Physics B, 1998
We derive the wave equation obeyed by electromagnetic fields in curved space-time. We find that t... more We derive the wave equation obeyed by electromagnetic fields in curved space-time. We find that there are Riemann and Ricci curvature coupling terms to the photon polarisation which result in a polarisation-dependent deviation of the photon trajectories from null geodesics. Photons are found to have an effective mass in an external gravitational field and their velocity in an inertial frame
Physics Letters A, 1990
The spin precession frequency of a charged particle confined to the equatorial plane in a circula... more The spin precession frequency of a charged particle confined to the equatorial plane in a circular orbit in Reissner-Nordstrom spacetime as a function of radial distance from the central object is investigated. In order to see the difference in behaviour for particles with different e/me and g values we consider the case of electron and proton separately. The spin precession frequency in the flat space limit puts a lower bound to Land&g value.
Arxiv preprint gr-qc/0109020, 2001
Classical and Quantum Gravity, 2003
We study interactions of electromagnetic fields with the curvature tensor of the form λR µναβ F µ... more We study interactions of electromagnetic fields with the curvature tensor of the form λR µναβ F µν F αβ. Such coupling terms though are invariant under general coordinate transformation and CPT, however violate the Einstein equivalence principle. These couplings do not cause any energy dependent dispersion of photons but they exhibit birefringence. We put constraints on the coupling constant λ using results from solar system radar ranging experiments and millisecondpulsar observations. We find that the most stringent constraint comes from pulsar observations and is given by λ < 10 11 cm 2 obtained from the timing of binary pulsar PSR B1534+12..
Pramana, 1989
... Page 2. 450 KS Virbhadra and AR Prasanna Schwarzschild background) and by the Ernst solution ... more ... Page 2. 450 KS Virbhadra and AR Prasanna Schwarzschild background) and by the Ernst solution (wherein the space time metric is changed due to the magnetic field). ... DS ik . DS kl DS i! p Dr ~- u'UI--Dz - ukul D-~ = 2k(SklFi I -- SitFkl) , (2) which satisfy the Pirani constraint ...
Il Nuovo Cimento B, 1982
Summbary The possible existence of « negative-energy states » of positive-root solutions of the ... more Summbary The possible existence of « negative-energy states » of positive-root solutions of the effective potential for a charged particle in an electromagnetic field superposed on black-hole space-times is presented. Though, in general, such states occur for particles contrarotating with respect to the black hole, indications are there that in some cases corotating particles also might show the existence of such
Classical and Quantum Gravity, 1998
We consider here the structure of rotating compact objects endowed with a magnetic field in gener... more We consider here the structure of rotating compact objects endowed with a magnetic field in general relativity as models of pulsars. We discuss first the structure of rotating stars in the framework of Hartle taking different realistic equations of state and study their effects on bulk properties of the star. We consider the possibilty of rotating stars with a quark matter core. We further analyse the structure of the magnetic field in the interior of the star as affected by different equations of state as well as due to rotation.
Classical and Quantum …, 1998
We consider here the structure of rotating compact objects endowed with a magnetic field in gener... more We consider here the structure of rotating compact objects endowed with a magnetic field in general relativity as models of pulsars. We discuss first the structure of rotating stars in the framework of Hartle taking different realistic equations of state and study their effects on bulk properties of the star. We consider the possibilty of rotating stars with a quark matter core. We further analyse the structure of the magnetic field in the interior of the star as affected by different equations of state as well as due to rotation.
International Journal of Modern Physics D, 2003
Using the generalised set of fluid equations that include the "Coriolis force" along wi... more Using the generalised set of fluid equations that include the "Coriolis force" along with the centrifugal and pressure gradient forces, we have reanalysed the class of self-similar solutions, with the pseudo-Newtonian potential. We find that the class of solutions is well behaved for almost the entire parameter space except for a few selected combinations of γ and α for the co-rotating flow. The analysis of the Bernoulli number shows that whereas it remains positive for co-rotating flow for f > 1/3, for the counter-rotating flow it does admit both positive and negative values, indicating the possibility of energy transfer in either direction.
We study the radial pulsation frequencies of slowly rotating neutron stars in general relativisti... more We study the radial pulsation frequencies of slowly rotating neutron stars in general relativistic formalism using realistic equations of state. It is found that the pulsation frequencies are always an increasing function of rotation rate. The increasing rate of frequency depends on the nature of equations of state. Cameron [1] suggested that the vibration of neutron stars might excite motions that might have interesting astrophysical applications, which lead to a series of investigations of the vibrational properties of neutron stars. The earliest detailed calculations were done by Meltzer and Thorne [2] and Thorne [3], where they investigated the radial as well as nonradial oscillations using available equation of state, such as the Harrison-Walker-Wheeler equation of state. These and other early studies by Wheeler [4], Chau [5] and Occhionero [6] indicated that the majority
In this we briefly cover the covariant approach to describe inertial forces in general relativity... more In this we briefly cover the covariant approach to describe inertial forces in general relativity and in particular look at the behaviour of the cumulative drag index for stationary Kerr geometry.
Astronomy and Astrophysics
We analyze self-similar solution of advection dominated accretion flows around a black-hole. The ... more We analyze self-similar solution of advection dominated accretion flows around a black-hole. The effect of a pseudo-Newtonian potential is introduced perturbatively, i.e., by regarding the general relativistic effects to be small. Comparison is made with the exact global numerical solutions that exist in the literature. It is demonstrated that the perturbative analysis can give better representation and insight into the parameter space of the solution. We find over a large range of the viscosity parameter, that self-similarity could be an excellent approximation. However, for certain values of the viscosity parameter and the gas parameter gamma , the perturbation can have a singularity. Consequently, the assumption of self-similarity could be violated at distances far away from the central black hole. Implication of the perturbative analysis is discussed.
Monthly Notices of The Royal Astronomical Society, 1990
The dynamics of a thick disc of accreting magnetofluid with finite conductivity around a compact ... more The dynamics of a thick disc of accreting magnetofluid with finite conductivity around a compact object is presented here. For the special case of a stationary and axisymmetric disc, the Newtonian limit of the relativistic fluid equations neglecting self-gravity of the disc for a Schwarzschild metric is derived. Along with Maxwell's equations and Ohm's law, fluid equations are solved analytically
Black Holes, Gravitational Radiation and the Universe, 1999
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Papers by Aragam Prasanna