• Alok Kumar

      Articles written in Pramana – Journal of Physics

    • Construction of topological conformal field theories

      Alok Kumar

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      In this lecture I review the construction of two dimensional Topologiccal Conformal Field Theories fromN=2 superconformal theories. We show that a BRST structure emerges upon a twisting of theN=2 superconformal algebra. Moreover, the energy-momentum tensor of the twisted theory is BRST-exact and all the physical correlation functions are independeent of the two dimensional metric. We briefly mention several generalizations such as the construction of topological superconformal theories as well as the topological conformal theories on higher genus Riemann surfaces.

    • D-branes inpp-wave background

      Alok Kumar Rashmi R Nayak Sanjay

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      We show the existence of classical solutions ofD-branes as well as a system ofD3-branes oriented at an arbitrary angle with respect to each other, in a six-dimensionalpp-wave background obtained fromAdS3 × S3 ×R4, withR — R andNS — NS 3-from flux. The world volume coordinate of D5-brane lies along the six-dimensional pp-wave directions, whereas thepp-wave direction is transverse to the system of D3-branes. We also present moreD-brane bound state solutions by applyingT-duality symmetries. The system ofD3-branes oriented at an arbitrary angle is shown to preserve 1/16 supersymmetries. Finally a brief discussion of the open string construction is presented for both the cases.

    • Intersectingp — p′ branes inpp-wave background

      Anindya Biswas Alok Kumar Kamal L Panigrahi

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      Several supergravity solutions corresponding to bothDp, as well asDp—Dp′ systems, inNS-NS andR-R pp-wave background originating fromAdS3 xS3 xR4 are presented. The supersymmetry properties of these solutions are analysed along with a brief outline of the world sheet construction for thep — p′ branes.

    • Understanding the spreading of a Gaussian wave packet using the Bohmian machinery

      Alok Kumar Pan

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      A freely propagating Gaussian wave packet naturally spreads with time. Exploiting the machinery of the Bohmian model of quantum mechanics, the way the wave packet spreads is re-examined.

    • Ultrasonic wave propagation in thermoelectric $\rm{ZrX_{2} (X = S, Se)}$ compounds

      SHAKTI PRATAP SINGH GAURAV SINGH ALOK KUMAR VERMA P K YADAWA R R YADAV

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      In the present work,we have calculated temperature-dependent second- and third-order elastic constants (SOECs and TOECs) of thermoelectric zirconium disulphide $\rm{(ZrS_{2})}$ and zirconium diselenide $\rm{(ZrSe_{2})}$ using a simple interaction potential model. SOECs have been used for the calculation of ultrasonic velocity along different orientations of propagation. Thermal relaxation time and ultrasonic attenuation have been determined with the help of SOECs and thermal conductivity. Temperature-dependent specific heat, thermal energy density, elastic coupling constants and Grüneisen parameters are also calculated using SOECs and other parameters. The dominating cause behind ultrasonic attenuation, in the temperature range of 300–900 K, is the interaction of acoustical phonon and lattice phonon. In the present study, we observed that the thermal conductivity and energy density play significant roles in ultrasonic attenuation. Ultrasonic velocity and attenuation are correlated with other thermophysical properties extracting important information about the quality and nature of the materials which are useful for industrial applications.

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