• K P Sinha

      Articles written in Pramana – Journal of Physics

    • Plasmon-magnon interaction in magnetic semiconductors

      G Baskaran K P Sinha

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      In appreciably doped semiconductors (e.g. EuO, CdCr2S4, etc.) plasmon and magnon energies are comparable. Therefore, there will be resonant interaction between these modes of excitations. On the basis of a new microscopic theory formulated for plasmon-magnon interaction, the effect of this interaction on the energies and lifetimes of plasmons and magnons has been calculated using the double-time Green’s function. The energy shifts are very small and the lifetimes of plasmons,τp, and magnons,τm, are of the order of 10−2 and 10−3 sec respectively.

    • An electron in the field of phonons and magnons

      S S Shah K P Sinha

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      The behaviour of a conduction electron in the presence of two Bose fields, namely, phonons and magnons in ferromagnetic semiconductors is studied. The effects of both electron-magnon and electron-phonon interactions on the energy renormalization are calculated.

    • Gravitational charges,f-gravity and hadron masses

      C Sivaram K P Sinha

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      Two types of fundamental gravitational charges are suggested by quantization of the angular momentum (i.e. J=nħ, wheren is an integer or half integer) occurring in the uncharged and charged Kerr metrics. These charges turn out to bee/√a ande/a, wheree is the unit electric charge anda the fine structure constant. The use of strong (f) gravity leads to corresponding fundamental massesM1(f) ∼2.2×10−24 g andM2(f)∼2.3×10−23 g. It is postulated that the hadrons are composed of these fundamental entities (christened oms here). Thus mesons arediomic particles and baryons aretriomic particles. This has a close resemblance to the quark model but here we deal with gravitational charges. The charges constituting hadrons are bound together by strong (f) gravity which is super strong compared to nuclear forces. Various hadron masses are obtained as the vibrational excitations of these composite units. The above model is capable of accounting for quantum numbers such as spin, baryon number, strangeness and isospin.

    • Gauge theories of weak and strong gravity

      K P Sinha

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      A review of some recent papers on gauge theories of weak and strong gravity is presented. For weak gravity, SL(2, C) gauge theory along with tetrad formulation is described which yields massless spin-2 gauge fields (quanta gravitons). Next a unified SL(2n,C) model is discussed along with Higgs fields. Its internal symmetry is SU(n). The free field solutions after symmetry breaking yield massless spin-1 (photons) and spin-2 (gravitons) gauge fields and also massive spin-1 and spin-2 bosons. The massive spin-2 gauge fields are responsible for short range superstrong gravity.

      Higgs-fermion interaction can lead to baryon and lepton number non-conservation. The relationship of strong gravity with other forces is also briefly considered.

    • Black hole thermodynamics from a possible model for internal structure

      P Goswami K P Sinha

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      Treating a black hole as a relativistic gas of microblack holes (planckions) which have fermionic character, expressions for some thermodynamic quantities are obtained. These have the same structure as those obtained by Hawking by other considerations.

    • Some remarks on a model for internal structure of black holes

      P Goswami K P Sinha

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      Some clarifications about a model for the internal structure of black holes developed in an earlier paper are presented to remove confusion in the interpretation of certain results.

    • Symmetry breaking, phase transition and gravity

      K P Sinha

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      We discuss some recent work in which the non-minimal coupling of gravity with a self-interacting scalar field in the presence of matter can lead to a phase transition when the sign of gravitational interaction changes. It is found that gravity becomes repulsive above a critical temperature which may lie in the range 1024 to 1032K which obtains in the very early universe (10−35 to 10−43 sec) of the standard model. The results are intimately connected with big bang and possible removal of singularity.

    • Bose condensation of particle-antiparticle systems

      K P Sinha

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      We discuss some important papers that have appeared in the last twenty years on the possibility of Bose condensation in particle-antiparticle systems. Electron-hole systems in some semiconductors provide the background for a non-relativistic treatment. Bose condensation and the superfluid phase of the electron-hole fluid are strongly favoured. Next, pairing and the appearance of the superfluid vacuum state in fermion-antifermion system are considered from a relativistic viewpoint. Special attention is given to the pairs in the stateJP=0+. The pairing in the fundamental fermion-antifermion sea may provide the background subquantal level of reality of the universe.

    • Theoretical studies on magnetic superconductors

      R Jagadish K P Sinha

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      The discovery of magnetic superconductors has posed the problem of the coexistence of two kinds of orders (magnetic and superconducting) in some temperature intervals in these systems. New microscopic mechanisms developed by us to explain the coexistence and reentrant behaviour are reported. The mechanism for antiferromagnetic superconductors which shows enhancement of superconductivity below the magnetic transition is found relevant for rare-earth systems having less than half-filled f-atomic shells. The theory will be compared with the experimental results of SmRh4B4 system. A phenomenological treatment based on a generalized Ginzburg-Landau approach will also be presented to explain the anomalous behaviour of the second critical field in some antiferromagnetic superconductors.

      These magnetic superconductors provide two kinds of Bose fields, namely, phonons and magnons which interact with each other and also with the conduction electrons. Theoretical studies of the effects of the excitations of these modes on superconducting pairing and magnetic ordering in these systems will be discussed.

    • Nonsingular cosmological models: the massive scalar field case

      B S Sathyaprakash K P Sinha

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      The nonminimal coupling of a massive self-interacting scalar field with a gravitational field is studied. Spontaneous symmetry breaking occurs in the open universe even when the sign on the mass term is positive. In contrast to grand unified theories, symmetry breakdown is more important for the early universe and it is restored only in the limit of an infinite expansion. Symmetry breakdown is shown to occur in flat and closed universes when the mass term carries a wrong sign. The model has a naturally defined effective gravitational coupling coefficient which is rendered time-dependent due to the novel symmetry breakdown. It changes sign below a critical value of the cosmic scale factor indicating the onset of a repulsive field. The presence of the mass term severely alters the behaviour of ordinary matter and radiation in the early universe. The total energy density becomes negative in a certain domain. These features make possible a nonsingular cosmological model for an open universe. The model is also free from the horizon and the flatness problems.

    • Spin and mass content of linearized Poincaré gauge theories

      Eric A Lord K P Sinha

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      A unified gauge theory of massless and massive spin-2 fields is of considerable current interest. The Poincaré gauge theories with quadratic Lagrangian are linearized, and the conditions on the parameters are found which will lead to viable linear theories with massive gauge particles. As well as the 2+ massless gravitons coming from the translational gauge potential, the rotational gauge potentials, in the linearized limit, give rise to 2+ and 2 particles of equal mass, as well as a massive pseudoscalar.

    • A possible model for fifth force

      Ramanand Jha K P Sinha

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      Recent reanalysis of the data of the Eötvös experiment suggested the existence of a new force. We show that a negative energy massive scalar field minimally coupled to gravity in a background Schwarzschild metric naturally leads to a potential which can explain the small anomalous effect in the Eötvös experiment.

    • Dual nature of Ricci scalar and creation of spinless particles

      K P Sinha S K Srivastava

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      Manifestation of Ricci scalar like a matter field as well as a geometrical field, at high energy, has been noted earlier [9]. Here, its interaction with another scalar field is considered in four-dimensional curved space-time. This interaction leads to the production of a large number of pairs of spinless particle-antiparticle due to expansion of the early universe in the vacuum state (provided by temperature dependent Coleman-Weinberg like potential for Ricci field), where spontaneous symmetry breaking takes place.

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