• Volume 50, Issue 2

      February 1998,   pages  95-204

    • Relativistic fluid sphere on pseudo-spheroidal space-time

      Ramesh Tikekar V O Thomas

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      A new exact closed form solution of Einstein's field equations is reported describing the space-time in the interior of a fluid sphere in equilibrium. The physical 3-space,t=constant of its space-time has the geometry of a 3-pseudo spheroid. The suitability of this solution for describing the model of a relativistic superdense star is discussed and the stability of the model under radial pulsations is examined.

    • Causal dissipation in Robertson-Walker cosmological models

      J P Singh A Prasad R K Tiwari

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      Some of the Robertson-Walker cosmological models filled with a fluid with bulk viscosity have been derived which are consistent with causal thermodynamics. The models are discussed briefly.

    • Particle production in curved spacetime

      N G Sarkar S Biswas

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      Particle production in curved spacetime has been discussed through the method of complex time WKB approximation. We consider Dirac equation in non-flat spacetime to understand particle production as particle-antiparticle rotation. The method is also generalized to understand particle production through parametric resonance. To understand the method of CWKB we consider particle production in Kasner spacetime as an example.

    • Finite temperature Cornwall-Jackiw-Tomboulis formalism of Φ6 theory

      K P Satheesh K Babu Joseph

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      The finite temperature effective potential for a scalar field with Φ6 interaction is calculated by extending the CJT formalism for composite operators. It is found that unrenormalized terms appear in the effective potential due to the presence of an unrenormalized mass term. Nonzero turning points are obtained both for positive and negativeλ. High temperature expansion is performed and the results are analysed numerically. Graphical analysis indicates symmetry restoration whenT→0.

    • Spin observables of the NN interaction in a relativistic harmonic model with confined gluons and mesons

      K B Vijayakumar S B Khadkikar

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      Polarization observables for the nucleon-nucleon (NN) scattering are investigated in the frame work of relativistic harmonic model belowElab=250 MeV, with the inclusion of theσ andπ meson exchange. The results can be interpreted as the ‘Cheshire cat principle’ of NN interaction.

    • Ratio of the color suppressed decays Λb→ΛJ/ψ andB0KJ/ψ

      A K Giri R Mohanta

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      Based on the factorization approximation, we have estimated the ratio of the branching fractions for the color suppressed nonleptonic decays Λb→ΛJ/ψ andB0KJ/ψ. Treating thes-quark as heavy, we have used the HQET to calculate the hadronic matrix elements. The mesonic Isgur-Wise function is calculated in the quark model whereas for the baryonic IW function we have employed the bound state soliton picture. The results obtained agree very well with the recent CDF experimental data.

    • Triviality bound on lightest Higgs mass in next to minimal supersymmetric model

      S R Choudhury Mamta Sukanta Dutta

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      We study the implication of triviality on Higgs sector in next to minimal supersymmetric model (NMSSM) using variational field theory. It is shown that the mass of the lightest Higgs boson in NMSSM has an upper bound ∼10MW which is of the same order as that in the standard model.

    • Measurement and analysis of the excitation function and isomeric cross section ratios forα-induced reaction on Ir, Au, Re and Ta nuclei

      M Ismail

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      Excitation functions and a few isomeric cross-section ratios for production of (1)192Au,193Au,194Au,195Au and192Ir nuclides inα-induced reactions on191,193Ir, (2)197Tl,197mHg,198m,gTl,199Tl and200Tl nuclides inα-induced reaction in197Au and (3)183Re and184m,gRe nuclides inα-induced reaction in181Ta and185Re are obtained from the measurements of the residual activities by the conventional stacked-foils technique from threshold to 50MeV. The excitation function and isomeric cross-section ratios for nuclear reaction181Ta(α,n)184m,gRe are compared with the theoretical calculation using the code Stapre which is based on exciton model for pre-equilibrium phase and Hauser-Feshbach formalism taking angular momentum and parity into account for the equilibrium phase of the nuclear reaction. All other experimental excitation functions are compared with the calculations considering equilibrium as well as pre-equilibrium reaction mechanism according to the geometry dependent hybrid (GDH) model and hybrid model of Blann using the code Alice/91. The high energy part of the excitation functions are dominated by pre-equilibrium reaction mechanism whereas the low energy parts are dominated by equilibrium evaporation with its characteristic peak. The GDH model provides a potentially better description of the physical process (i.e., a higher probability for peripheral collisions to undergo precompound decay than for central collisions) compared to hybrid model. However in the energy range of present measurement most of the excitation functions are fitted reasonably well by both GDH model and hybrid model with initial exciton numberN0=4(Nn=2,Np=2,Nh=0). Barring a few reactions we have found the overall agreement between theory and experiment is reasonably good taking the limitations of the theory into account.

    • Jeans-Buneman instability in a dusty plasma

      B P Pandey G S Lakhina

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      A self consistent formulation of the Jeans instability of a dusty plasma with proper inclusion of charge dynamics is described. It is shown that charge fluctuations significantly affect the Jeans as well as the Buneman mode. For plasma particles (electrons and ions) in local thermal equilibrium, the Jeans lengthλJ is given byλJλgF(R, ε, β/η), whereλg is the Debye length of the charged grains,R is the square of the ratio of the Jeans to the plasma frequency of the grains,ε is the square of the ratio of the Debye length of the grains and the plasma particles andβ/η is the ratio of the attachment to the decay frequency of the electronic charges to the grain surface. The functional form ofF is given in the text. Numerical investigation of the Jeans-Buneman mode for a two and three component plasma shows that the Jeans mode dominates atD≪1 (wherek is the wave number andλD is the Debye length of plasma particles), whereas atD≫1 only the Buneman mode operates. Charge fluctuations reduce the area of overlap of the two modes. Furthermore, in the absence of gravity, there exists a new, charge fluctuation induced unstable mode in a streaming dusty plasma. Astrophysical applications of the results are discussed.

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