Scientific Contributions

If one looks at the research papers of Prof. Pradhan, they stand out not only for the quality of research, relevance of his research in the present context but also for his broad interests. He has done excellent work not only in quantum field theory and high energy physics, but also in the areas of atomic collisions, plasma physics and electron gas. This one can perhaps attribute to his mastery over fundamentals, his broad based interest and high quality of graduate courses that he took at University of Chicago from famous scientists like Enrico Fermi. His commitment to research is amazing. In Saha Institute of Nuclear Physics, Kolkata where he was a faculty for 12 years, he would be at his desk by eight thirty in the morning and would be carrying out his research till about five in the evening.

His first paper in 1957 based on his Ph.D. thesis was a single author paper on atomic collisions. In this paper he essentially introduced the impulse approximation in atomic collisions and this paper has received wide attention and has also been mentioned in the books on atomic collisions. His second paper (also a single author paper) was about Landau damping in plasma oscillations in a uniform magnetic field and it came in the same year which has also received wide attention and been mentioned in books. In 1959 he wrote his first paper (again a single author paper) in the area of quantum field theory while in 1960 he had a paper about dielectric constant of a dense electron gas with a collaborator. His first four papers were not only of high quality but also in four entirely different fields which is very unusual. He continued to write papers on plasma physics and electron gas till 1970 while he had his last paper on atomic collisions as late as in 1994.

After 1970, Prof. Pradhan’s papers are primarily in the areas of quantum field theory and high energy physics. If one looks at these papers it is clear that Prof. Pradhan never followed the current fashion but always worked on his own ideas. Further, most of his ideas were rather novel and unconventional. By 1965 it had been proved that a massless particle with spin one or greater than one cannot have electric charge. In 1965, in a paper in Nuovo Cimento, he tried to extend that proof to spin half particles. Another of his novel work was 1975 paper in Physical Review D where he and his collaborator showed that a la Regge poles, there are also poles of the scattering amplitude in the complex scale dimension plane. They wrote several papers trying to look for such poles in potential scattering as well as in quantum electrodynamics and also tried to relate it to scaling violation. He wrote one of the earliest paper about what is popularly known as Schwinger term. in 1998 he presented models for composite quarks, leptons as well as photon. In recent years the idea of 1fundamental length has received lot of attention. Prof. Pradhan thought about it several years before.

One of his work with profound insight is about magneto-electric effect. Unfor- tunately, he was ahead of his time. One might recall that in recent years multifer- roics and magneto-electric materials has received wide attention both theoretically and experimentally. Prof. Pradhan got interested in magneto-electric materials in early eighties. In one paper he with his collaborator showed that the vacuum of the 2+1 dimensional quantum electrodynamics with Chern-Simons term shows magneto- electric effect. In 2006 in a paper in Physica Scripta he looked at the Raman spectra of magneto-electric crystals.

Prof. Pradhan was naturally attracted to symmetries and has made subtle use of them in several of his papers. For example, the idea of para supersymmetry greatly attracted him and discussions with him has motivated others in the institute to write paper about it. Another aspect of his work which stands out is nonperturbative nature of his studies. For example, he along with his collaborator calculated electron self mass to all order in fine structure constant α but to first order in Planck’s constant. Other ideas which attracted him were local duality and scale and conformal symmetries. But one idea which he followed over more than two decades is that of magnetic monopoles. Particular mention may be made of his work where he suggested the possible existence of magnetic charge in Stark states of hydrogen atom. He wrote several papers about it in the last 25 years, the latest one being as late as in 2017 when he was 88 year old. In fact in 2017 he wrote three papers, the other two being about the resolution of EPR paradox through long range force between spins and the other about the existence Lagrange points in the circular orbits of hydrogen using Bohr’s theory. I might add here that he has written several papers about long range force between spins.

(Contributed by Professor Avinash Khare)