• Arvind Kumar

      Articles written in Pramana – Journal of Physics

    • Dirac equation in Kerr space-time

      B R Iyer Arvind Kumar

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      The weak field-low velocity approximation of Dirac equation in Kerr space-time is investigated. The interaction terms admit of an interpretation in terms of a ‘dipole-dipole’ interaction in addition to coupling of spin with the angular momentum of the rotating source. The gravitational gyro-factor for spin is identified. The charged case (Kerr-Newman) is studied using minimal prescription for electromagnetic coupling in the locally inertial frame and to the leading order the standard electromagnetic gyro-factor is retrieved. A first order perturbation calculation of the shift of the Schwarzschild energy level yields the main interesting result of this work: the anomalous Zeeman splitting of the energy level of a Dirac particle in Kerr metric.

    • Green’s functions for spin half field theory in Rindler space

      B R Iyer Arvind Kumar

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      The solutions of Dirac equation in different regions of the complete extension of Rindler space are obtained near the event horizons and in the asymptotic limits. Continuity of these solutions across the event horizons is established. The Green’s functions are written down in the two causally disconnected regions, continued in the future (F) and past (P) regions using the techniques a la Boulware and a consistent scheme of Green’s functions in all regions is exhibited.

    • Spontaneous creation of massive spin half particles by a rotating block hole

      B R Iyer Arvind Kumar

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      The techniques of second quantization in Kerr metric for the scalar and neutrino (massless) fields are extended to the massive spin half case. The normal modes of Dirac field in Kerr metric are obtained in Chandrasekhar’s representation and the field is quantized as usual by imposing equal-time anti-commutation relations. The vacuum expectation value of energy-momentum tensor is evaluated asymptotically, leading to the result that a Kerr black hole spontaneously creates, in addition to scalar and neutrino quanta, massive Dirac particles in the classical superradiant modes.

    • Hawking radiation of scalar and Dirac quanta from a Kerr black hole

      B R Iyer Arvind Kumar

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      Unruh’s technique of replacing collapse by boundary conditions on the past horizon (theξ-quantisation scheme) for the derivation of the well-known Hawking radiation is extended to the Kerr black hole for the scalar and especially for the spin half field. The expectation value of the energy momentum tensor is evaluated asymptotically in theξ-vacuum state yielding explicitly the net Hawking flux of scalar and spin half quanta. The appropriate statistical distribution that emerges naturally for Dirac quanta validates the ξ-scheme for fermions and confirms the association of temperature with a Kerr black hole.

    • Collision cross-sections for scattering of electrons from NO molecule

      Arvind Kumar Jain Pradeep Kumar A N Tripathi

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      Electron-NO scattering is investigated in the energy range 2–1000eV by using a parameter-free spherical complex optical potential (SCOP) approach in the fixed nuclei approximation. The real part of the optical potential consists of three potentials namely, the static, the exchange and the polarization. For the imaginary part of the SCOP, we employ a semi-empirical model absorption potential. The molecular charge density function is calculated from a single-configuration molecular orbital based on Slater type orbitals. The various potential terms are then determined from these charge density functions. Calculations of the elastic (with and without absorption effects), total absorption, momentum transfer and differential cross-sections are obtained and compared with the available theoretical results and experimental measurements.

    • Commissioning and validation of the injector and electron beam transport systems for the IR-FEL at RRCAT

      SONA CHANDRAN BHASKAR BISWAS SHANKAR LAL ARVIND KUMAR R S SAINI M KHURSHEED SAKET KUMAR GUPTA PRAVIN NERPAGAR R K PANDIT K K PANT

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      The first observation of lasing in an infra-red free electron laser (IR-FEL) at the Raja Ramanna Centre for Advanced Technology has been reported recently with a measured power output, i.e. $\sim10^{5}$ times higher than the expected spontaneous radiation power for the electron beam parameters used in the experiment. IR-FEL design simulations, however, estimate a power gain of $10^{7}$ which is three orders of magnitude higher than the experimentally achieved value. To understand this difference between the measured and the expected power output from the IR-FEL, the electron beam used in the experiments has been characterised and FEL simulations have been repeated after considering the measured electron beam parameters. A reasonably good agreement is obtained between the measured results and those predicted by FEL simulations. Experiments have also been performed to study the expected variation in electron beam properties over a macropulse, which should be minimum for an oscillator FEL like the IR-FEL. This paper reports the results from the experiments for characterisation of the electron beam in the IR-FEL set-up and the results from FEL simulations, considering these measured electron beam parameters.

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