• G Ramachandran

      Articles written in Pramana – Journal of Physics

    • Neutrino scattering on polarized deuterons

      M V N Murthy G Ramachandran K V L Sarma

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      The possible presence of anI=0 axial vector piece in the hadronic neutral current may be detected by looking for an asymmetry in the emission of the recoil deuterons in elastic scattering of neutrinos or antineutrinos on polarized deuterons. It is estimated that this asymmetry could be about 40% with the incident neutrinos in the energy range of tens of MeV.

    • Magnetic contributions to high energy inverse bremsstrahlung process

      G Ramachandran R S Keshavamurthy

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      Magnetic contribution to inverse bremsstrahlung is estimated at high energies. It begins to dominate over the Coulomb contribution in the ratioCE22 tan2 (θ2/2) (1+sin2 (θ2/2)) whereE2 andθ2 denote the energy and angle of the accelerated electron andC is essentially a nuclear constant.

    • SU(3) representation for the polarisation of light

      G Ramachandran M V N Murthy K S Mallesh

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      A new mathematical representation for discussing the state of polarisation of an arbitrary beam of partially polarised light is described which makes use of the generators of the group SU(3). This representation is sufficiently general to describe not only physical photons which are transverse but also virtual photons. The correspondence between our representation and the conventional Stokes parameter representation is established and this leads to an equivalent geometrical description of partially polarised light in terms of diametrically opposite points on a Poincarè sphere with radius equal to the degree of polarisation. The connection with the spherical tensor representation is also discussed and this leads to a simple geometrical interpretation of the bounds on the parameters characterizing an arbitrary beam of partially polarised light.

    • $$^3 \overrightarrow {He} $$ (γ, π°)$$^3 \overrightarrow {He} $$ as the nuclear probeas the nuclear probe

      G Ramachandran R S Keshavamurthy K Venkatesh

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      The state of polarization of the recoil nucleus inγ+3He→π°+3He as well as the asymmetry in the differential cross-section when the initial3He is polarized are studied together with the differential cross-section taking into consideration theS, S′ andD-state admixtures in the nuclear wavefunctions. In view of the considerable spin dependence in the photoproduction amplitudes these observables are found to be quite sensitive to the small admixtures ofS′ andD-states in the nuclear wave-functions.

    • Weak neutral current effects in elastic electron deuteron scattering

      M V N Murthy G Ramachandran S K Singh

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      We study the effect of weak neutral currents in elastic electron deuteron scattering on both unpolarized and polarized deuteron targets. Theoretical expressions have been derived for the polarized electron asymmetry, polarized target asymmetry and recoil deuteron vector polarization within the framework of impulse approximation. We show that these polarization parameters can give vital information on the space-time and isospin structure of the hadronic weak neutral current. In particular, our numerical estimates show that a measurement of polarized target asymmetry is sensitive to the isoscalar axial vector piece in the hadronic neutral current which, though zero in the Weinberg-Salam model, is not completely ruled out by the data.

    • Photon emission from non-oriented spin systems

      G Ramachandran V Ravishankar

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      A method is suggested to determine experimentally whether the state of a spin system is oriented or non-oriented by measuring the angular distribution,I and the circular polarization asymmetry,Ac of the photons emitted by the system. These also provide enough data to determine the density matrix completely.

    • Polarization parameters in systems with spin-spin interactions

      K S Mallesh G Ramachandran

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      The spin-spin interaction of two arbitrary spin systems is considered in some detail. The temporal evolution of the polarization parameters and the correlation parameters has been worked out. Applications of the formalism and the interpretation of the results to processes such as heavy-ion interactions, muon and nuclear repolarization and depolarization in muonic atoms and interactions of multilevel systems are outlined.

    • Inelastic scattering of pions on7Li

      S B Patangi G Ramachandran

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      The recent experimental results of Gibson and coworkers, for inelastic scattering of pions on7Li, leading to the first five excited states of7Li are analyzed using a shell model description including configuration admixtures and representing the transition nucleon densities following Helm model, used extensively in the context of inelastic scattering of electrons. With the transition radii for protons and neutrons chosen to be 3.9 fm and 4.1 fm respectively, good fits to the experimental cross sections are obtained. In contrast to the distorted wave Born approximation (dwba) calculations using optical model codes, we find the present work is able to reproduce the observed maxima and minima precisely. Moreover this analysis reveals the importance of considering the configuration admixtures especially in the transitions to24P5/2 (7.48 MeV) and24D7/2 (9.67 MeV) levels.

    • On πd elastic scattering using aligned deuteron targets

      A Sudha Rao G Ramachandran

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      A theoretical study is made of the advantages to be gained in polarizing a deuteron target by applying an external electric quadrupole field with non-zero asymmetry parameter for carrying outd(π, π)d experiments, in order to determine empirically the helicity amplitudes A, B, C, D characterizing the scattering, without any phase ambiguities.

    • Photon polarisation asymmetries in (p,p′γ) experiments

      A R Usha Devi A Sudha Rao G Ramachandran

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      The Stokes parameters characterising the polarization of the photon in theγ-decay of12C*(1+) are examined in correlation with the scattered proton in12C(p,p′)12C*(1+). This opens up the possibility of efficiently determining empirically the six inelastic scattering amplitudes utilizing only 13 measurements. We identify several alternative sets of such measurements to encourage experimental efforts in this direction.

    • Polarized light

      G Ramachandran A R Usha Devi N S Saandeep Kannada Vardhana

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      Following the recent work of Chandleret al on quasi probability distributions for spin-1/2 particles, we show that polarized light can be interpreted in terms of trivariate probability distributions in two different ways by choosing the variates to correspond to (i) the co-ordinates on the Poincare sphere, (ii) the components of the spin operator of the photon. In either case, it is shown that the Margenau-Hill procedure leads to probability mass functions while the Wigner-Weyl approach leads to probability density functions and the well-known Stokes parameters are also realised as appropriate averages with respect to these distribution functions.

    • Spin squeezing and quantum correlations

      KS Mallesh Swarnamala Sirsi Mahmoud AA Sbaih PN Deepak G Ramachandran

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      We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among the spinors in the coupled state.

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