• T Padmanabhan

      Articles written in Pramana – Journal of Physics

    • Solutions of scalar and electromagnetic wave equations in the metric of gravitational and electromagnetic waves

      T Padmanabhan

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      The wave equation for a scalar field ϕ and vector potentialA* are solved in the background metric of a gravitational wave. The corresponding solutions when the metric is generated by a plane electromagnetic wave, is obtained from these solutions. The solution for the scalar wave is discussed in detail. It is found that because of the interaction, two new waves are generated in the lower order approximations. One of them has the same phase dependence as the original wave while the other shows a transient character. There is no interaction when the waves are along the same direction.

    • A definition for time in quantum cosmology

      T Padmanabhan

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      A definition for the intrinsic time co-ordinate is proposed, using the phase of the wave function of the universe. This definition generalizes the notion of time co-ordinate which arises in the semiclassical cosmology. It also leads to acceptable results for the evaluation of expectation values of physical variables.

    • Mach’s principle and the notion of time

      T Padmanabhan

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      The role of time coordinate in the realization of March’s principle is highlighted. It is shown that Mach’s principle is linked to the definition of a ‘particle’. These results suggest a deep connection between quantum gravity and Mach’s principle.

    • Vacuum polarization around an Aharonov-Bohm solenoid

      T Padmanabhan

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      The quantisation of a charged scalar field in an externally specified electromagnetic field, described by the vector potentialAi=∂if withf(t,r,θ,z)= is discussed. The electromagnetic field is zero everywhere except at the origin; a singular magnetic field (Aharonov-Bohm field) exists at the origin. The vacuum polarization around such a magnetic field is computed and the non-local behaviour is discussed.

    • Quantum theory in external electromagnetic and gravitational fields: A comparison of some conceptual issues

      T Padmanabhan

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      The quantum theories of a scalar field interacting with external electromagnetic and gravitational fields respectively are compared. It is shown that several peculiar features, like the ambiguity of particle definition, thermal effects etc., which are thought to be special to quantum theory in curved spacetime, have analogues in the case of electromagnetism.

    • CosmologicalN-body simulations

      J S Bagla T Padmanabhan

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      In this review we discuss cosmologicalN-body codes with a special emphasis on particle mesh codes. We present the mathematical model for each component ofN-body codes. We compare alternative methods for computing each quantity by calculating errors for each of the components. We suggest an optimum set of components that can be combined to reduce the overall errors inN-body codes.

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