Sai Iyer

Scalar waves in the Boulware-Deser black-hole background

Scalar waves are studied on the Boulware-Deser black-hole background. The Klein-Gordon equation is separated into radial and angular parts. The angular functions are written in terms of Gegenbauer polynomials. The radial equation is cast into the Schrodinger form and employed to investigate the effect of the string parameter alpha on the scattering of scalar waves and quasi-normal modes.

Centrifugal force and ellipticity behaviour of a slowly rotating ultra-compact object

Using the optical reference geometry approach, we have derived a general expression for the ellipticity of a slowly rotating fluid configuration using a Newtonian force balance equation in the conformally projected absolute 3-space, in the realm of general relativity. Further, with the help of the Hartle - Thorne (H - T) metric for a slowly rotating compact object, we have evaluated the centrifugal force acting on a fluid element and also evaluated the ellipticity and found that the centrifugal reversal occurs at around , and the ellipticity maximum at around . The result has been compared with that of Chandrasekhar and Miller which was obtained in the full 4-spacetime formalism.

Centrifugal force in Kerr geometry

Using the 3+1 splitting of optical reference geometry, the authors have obtained the correct expression for the centrifugal force acting on a particle at the equatorial circumference of a rotating body in the locally non-rotating frame of the Kerr geometry. In contrast to the analysis based on Boyer-Lindquist coordinates, this expression is valid everywhere outside the event horizon.

Behaviour of the centrifugal force and of ellipticity for a slowly rotating fluid configuration with different equations of state

We have evaluated the centrifugal force acting on a fluid element and the ellipticity of the fluid configuration, which is slowly rotating, using the Hartle - Thorne solution for different equations of state. The centrifugal force shows a maximum in every case, whereas the reversal in sign could be seen in only one case and the system becomes unstable in other cases. The ellipticity as calculated from the usual definition shows maxima, whereas the definition obtained from the equilibration of the inertial forces, shows a negative behaviour, indicating that the system is prolate and not oblate. This prolate shape of the configuration is similar to the one earlier found by Pfister and Braun for a rotating shell of matter, using the correct centrifugal force expression for the interior. The location of the centrifugal maxima gets further away from the Schwarzschild radius as the equation of state gets softer.

CUMULATIVE DRAGGING : AN INTRINSIC CHARACTERISTIC OF STATIONARY AXISYMMETRIC SPACETIME

Abstract The cumulative drag index defined recently by Prasanna has been generalised to include the centrifugal acceleration. We have studied the behaviour of the drag index for the Kerr metric and the Neugebauer-Meinel metric representing a self-gravitating rotating disk and their Newtonian approximations. The similarity of the behaviour of the index for a given set of parameters, both in the full and approximated forms, suggests that the index characterises an intrinsic property of spacetime with rotation. Analysing the index for a given set of parameters shows possible constraints on them.

The radial force on a charged particle in superimposed magnetic fields on Schwarzschild spacetime

Following the approach of optical reference geometry we derive the expression for the total force in the radial direction acting on a charged particle in magnetic fields superimposed on the static Schwarzschild background and show the possible existence of bound orbits for particles in the field of ultra compact objects at distancesr⩽3m wherein the Lorentz force counterbalances both the gravitational and centrifugal forces.

Padé approximants for truncated post-Newtonian neutron star models

Padeapproximants to truncated post-Newtonian neutron star models are constructed. The Pademodels converge faster to the general relativistic ~GR! solution than the truncated post-Newtonian ones. The evolution of initial data using the Pademodels approximates better the evolution of full GR initial data than the truncated Taylor models. In the absence of full GR initial data ~e.g., for neutron star binaries or black hole binary systems!, Padeinitial data could be a better option than the straightforward truncated post-Newtonian ~Taylor! initial data.

Kinematical Consequences of Inertial Forces in General Relativity

One of the most important concepts of physics, which in fact marked the foundation of physics is the concept of inertia. Inertia as enunciated by Newton is an indicator of the characteristic of a body that determines its motion. Whereas according to Newton’s law of motion, a body’s state of rest or of uniform motion does in no way characterise its inertia, any change in this state depends upon its inertia. As the change of state can be recorded only through acceleration of the body, the significance of inertia can indeed be understood only by the action of external agencies influencing a body.