• S Biswas

      Articles written in Pramana – Journal of Physics

    • Particle production, back reaction and singularity avoidance

      A Shaw D Biswas B Modak S Biswas

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      We consider particle production in Robertson-Walker spacetime as particle-antiparticle rotation. We thereby obtain a scale factor that guarantees particle production. We then study quantum field effects in spatially flat homogeneous and isotropic spacetime with energy density of created particles and one loop quantum correction as back reaction. In the numerical solution initial values are determined from particle production simulated scale factor and obtain the evolution of the universe both at early and late times having a bounce.

    • The CWKB approach to non-reflecting potential and cosmological implications

      S Biswas I Chowdhury

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      We discuss the method of calculating the reflection coefficient using complex trajectory WKB (CWKB) approximation to understand the non-reflecting nature of the potentialU(x) = -U0/cosh2(x/a). We show that the repeated reflections between the turning points whose paths are in conformity with Bogolubov transformation technique are essential in obtaining the non-reflecting condition. We also discuss the implications of the results when applied to the particle production scenario. We use the CWKB technique developed by one of the authors (SB) to obtain the results which agree very well with those obtained by exact quantum mechanical calculations.

    • Calculation of CWKB envelope in boson and fermion productions

      S Biswas I Chowdhury

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      We present the calculation of envelope of boson and of both low- and high- mass fermion production at the end of inflation when the coherently oscillating inflatons decay into bosons and fermions. We consider three different models of inflation and use CWKB technique to calculate the envelope to understand the structure of resonance band formation. We observe that though low-mass fermion production is not effective in pre-heating because of Pauli blocking, it is quite probable for high-mass fermion to take part in pre-heating.

    • Spectroscopy of fission fragments using prompt-delayed coincidence technique

      R Palit S Biswas

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      The time-stamp structure of the digital data acquisition system of the Indian National Gamma Array (INGA) has been utilized to carry out prompt-delayed coincidence technique for the spectroscopic study of fission fragments. This technique was found to be useful to determine the states above the long-lived isomer (with half-life up to $\sim$5 𝜇s), present in the fission fragments. The angular correlation of 𝛾-rays, emitted by the fission fragments, has also been used in the present INGA geometry to determine the spins of the de-exciting states.

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