Articles written in Pramana – Journal of Physics

    • Exclusive hadronic processes and color transparency

      Pankaj Jain John P Ralston

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      We review the current status of high energy exclusive processes and color transparency.

    • The proton electromagnetic form factorF2 and quark orbital angular momentum

      Pankaj Jain John P Ralston

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      We analyse the proton electromagnetic form factor ratioR(Q2) =QF2(Q2)/F1(Q2) as a function of momentum transferQ2 within perturbative QCD. We find that the prediction for (R(Q2) at large momentum transferQ depends on the exclusive quark wave functions, which are unknown. For a wide range of wave functions we find thatQF2F1 ∼ const. at large momentum transfer, which is in agreement with recent JLAB data.

    • Pseudoscalar-photon mixing and the large scale alignment of QSO optical polarizations

      Pankaj Jain Sukanta Panda S Sarala

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      We review the observation of large scale alignment of QSO optical polarizations. Alignment is seen in patches of distance scale of order 1 Gpc. We argue that the existence of a hypothetical light pseudoscalar can explain these observations.

    • Proton electromagnetic form factors at large momentum transfer

      Pankaj Jain Subhadip Mitra

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      We review the current experimental and theoretical status of the proton electromagnetic form factors.

    • The dynamical mixing of light and pseudoscalar ¯elds

      Sudeep Das Pankaj Jain John P Ralston Rajib Saha

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      We solve the general problem of mixing of electromagnetic and scalar or pseudoscalar fields coupled by axion-type interactions $L_{\text{int}} = g_{\phi}\phi \epsilon_{\mu \nu \alpha \beta} F^{\mu \nu} F^{\alpha \beta}$. The problem depends on several dimensionful scales, including the magnitude and direction of background magnetic field, the pseudoscalar mass, plasma frequency, propagation frequency, wave number, and finally the pseudoscalar coupling. We apply the results to the first consistent calculations of the mixing of light propagating in a background magnetic field of varying directions, which show a great variety of fascinating resonant and polarization effects.

    • Photon-induced low-energy nuclear reactions


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      We propose a new mechanism for inducing low-energy nuclear reactions (LENRs). The process is initiated by a perturbation which we assumed to be caused by absorption or emission of a photon. Due to the electromagnetic perturbation, the initial two-body nuclear state forms an intermediate state to make a transition into the final nuclear state through the action of another perturbation. In the present paper,we take the second perturbation to be also electromagnetic. We need to sum over all energies of the intermediate state. Since the upper limit on this sum is infinity it is possible to get contributions from very high energies for which the barrier penetration factor is not too small. By considering a specific reaction, we determine the conditions under which this mechanism may lead to significantly enhanced reaction rates. We find that the mechanism leads to very small cross-sections in free space. However, in a condensed medium, there exist several possibilities leading to enhanced cross-sections, which may lead to observable reaction rates even at relatively low energies. Hence we argue that LENRs are possible and provide a theoretical set-up which may explain some of the experimental claims in this field.

    • A toy model for low-energy nuclear fusion


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      We study the fusion of a proton with a nucleus with the emission of two photons at low incident energy of the order of eV or smaller.We use a step model for the repulsive potential between the proton and the nuclei.We consider the reaction both in free space and inside a medium.We make a simple model for the medium by assuming a hard wall potential beyond a certain length scale. This essentially leads to discretisation of the energy spectrum which is expected inside a medium and is seen both for a crystalline lattice structure and for amorphous materials. We use second-order perturbation theory to compute the transition rate. We find that the rate in free space is very small. However, in the medium, the rate may be substantial. Hence, we conclude that nuclear fusion reactions maytake place at low energies at observable rates.

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