K P Sinha
Articles written in Pramana – Journal of Physics
Volume 1 Issue 1 July 1973 pp 31-36 Solids
Plasmon-magnon interaction in magnetic semiconductors
In appreciably doped semiconductors (e.g. EuO, CdCr_{2}S_{4}, 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,
Volume 2 Issue 4 April 1974 pp 189-195 Solids
An electron in the field of phonons and magnons
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.
Volume 2 Issue 5 May 1974 pp 229-238 Nuclear And Particle Physics
Gravitational charges,
Two types of fundamental gravitational charges are suggested by quantization of the angular momentum (
Volume 23 Issue 2 August 1984 pp 205-214 Nuclear And Particle Physics
Gauge theories of weak and strong gravity
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(2
Higgs-fermion interaction can lead to baryon and lepton number non-conservation. The relationship of strong gravity with other forces is also briefly considered.
Volume 23 Issue 3 September 1984 pp 381-384 Relativity
Black hole thermodynamics from a possible model for internal structure
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.
Volume 25 Issue 2 August 1985 pp 223-224 Comments
Some remarks on a model for internal structure of black holes
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.
Volume 25 Issue 4 October 1985 pp 343-347 Relativity And Gravitation
Symmetry breaking, phase transition and gravity
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 10^{24} to 10^{32}K 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.
Volume 25 Issue 4 October 1985 pp 467-472 Particle Physics
Bose condensation of particle-antiparticle systems
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 state
Volume 28 Issue 5 May 1987 pp 565-571
Theoretical studies on magnetic superconductors
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 SmRh_{4}B_{4} 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.
Volume 30 Issue 1 January 1988 pp 15-27 Gravitation
Nonsingular cosmological models: the massive scalar field case
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.
Volume 30 Issue 6 June 1988 pp 511-519 Particle Physics
Spin and mass content of linearized Poincaré gauge theories
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.
Volume 31 Issue 2 August 1988 pp 93-97 Gravitation
A possible model for fifth force
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.
Volume 44 Issue 4 April 1995 pp 333-345
Dual nature of Ricci scalar and creation of spinless particles
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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