Ramamurti Rajaraman (11 March 1939 – 12 July 2025) was an Indian theoretical physicist who was an emeritus professor of theoretical physics at the School of Physical Sciences at Jawaharlal Nehru University. He was also the co-Chairman of the International Panel on Fissile Materials and a member of the Bulletin of the Atomic Scientists' Science and Security Board. He taught and conducted research in physics at the Indian Institute of Science, the Institute for Advanced Study at Princeton, and as a visiting professor at Stanford, Harvard, MIT, and elsewhere. He received his doctorate in theoretical physics in 1963 from Cornell University. In addition to his physics publications, Rajaraman wrote widely on topics including fissile material production in India and Pakistan and the radiological effects of nuclear weapon accidents.
Early life and education Rajaraman was brother to physicist Ramamurti Shankar. He completed his BSc from St. Stephen's College of Delhi University in 1958 and his PhD in theoretical physics from Cornell University in 1963, with Hans Bethe as his supervisor. After a brief postdoctoral stint at TIFR in 1963, he returned to Cornell to teach and continue research. In 1969, after spending two years at the Institute for Advanced Study at Princeton he returned to India, working first at Delhi University (1969–76), then Indian Institute of Science (IISc), Bangalore (1976–93), finally JNU (1994– ) where he was Emeritus Professor. He spent sabbaticals at Harvard University, MIT, Stanford University, CERN, the University of Illinois and the Institute for Advanced Study in Princeton.
Academic and research achievements A notable feature of Rajaraman's research is the diversity of the areas on which he worked. In theoretical physics his work spanning four decades (1962–2002) covers nuclear many-body theory, elementary particles, quantum field theory, soliton physics, quantum Hall effect and aspects of Statistical Mechanics. In addition, after 2000, he was deeply engaged in technical and advocative work on public policy, including global nuclear disarmament, India's civilian and military nuclear programmes and higher education. Given below is a summary of some of this work.
Nuclear many-body theory In 1962–63, as part of his PhD thesis, Rajaraman demonstrated that the prevalent calculations of the energy of nuclear matter in powers of the Brueckner reaction matrix would not yield a convergent result. He suggested instead summing, in closed form, interactions to all orders among any given number of nucleons, thereby generating a density expansion. He also outlined a method for doing so. Subsequently, Hans Bethe converted Rajaraman's outline into a substantive theory for the three-nucleon problem in nuclear matter. These developments, summarised in the 1967 review article by Rajaraman with Bethe, eventually led to the Coupled Cluster method in Many Body theory. Subsequently, B.H.J. McKellar, Rajaraman studied the impact on of intrinsic three-body and higher many-body forces between nucleons, (as distinct from the familiar pairwise nuclear forces) on nuclear matter. Separately Rajaraman showed that nucleon-nucleon correlations suppress pion condensation in neutron stars.
Regge poles and particle phenomenology During the 1970s, Rajaraman extended his research to include particle physics. At that time, high energy hadron scattering was being analysed using S-matrix and Regge pole techniques. Since the Froissart-Martin asymptotic bounds on hadron scattering is not applicable to Weak Interactions, Rajaraman constructed a self-consistent theory of zero-mass neutrinos and showed that ν- ν and ν- ν(bar) scattering total cross sections asymptotically become equal and approach the same constant value. Rajaraman gave the first determination from experimental data of the value of the "Triple Pomeron Vertex" as a function of momentum transfer and also derived the consequences of the vanishing of this vertex on high energy hadron scattering. With Finkelstein, he analysed Exchange Degeneracy in inclusive reactions involving the triple-Reggeon vertex. With S. Rai Choudhary and G. Rajasekaran, he obtained several results on deep inelastic electron scattering data being then generated at SLAC. These included (i) constraints on its Structure Functions, (ii) its relationship to purely hadronic inclusive scattering (N+N→N+ X) and (iii) discovery of a fixed pole in virtual Compton Scattering.
Solitons Aside from his reviews and his book, Rajaraman's original results on solitons include exact soliton solutions of coupled scalar field theories and with E. Weinberg a method for quantizing Solitons with internal symmetries. In 1982, Rajaraman and the theorist John Bell, examined the curious phenomenon of quantum states with fractional fermion number, discovered theoretically by Jackiw and Rebbi and experimentally observed in polyacetylene. These findings seemed to violate common sense at first sight. Rajaraman and Bell clarified this puzzle, in a pair of papers, one addressing the problem in the continuum Dirac theory, and the other in a lattice model of polyacetylene. They showed that the missing fraction of the electron was lurking at the edges of the system, as has also been seen since then in some experiments.
Gauge anomalies In 1985, R. Jackiw and Rajaraman showed that gauge theories with anomalies are not necessarily inconsistent, contrary to the general belief till then. They solved the Chiral Schwinger Model (CSM), which is anomalous, exactly and proved that it has a consistent and relativistically covariant spectrum. Following this Rajaraman demonstrated using Dirac's theory of Constraints that the presence of a gauge anomaly only alters the constraint structure of the theory so that although it is no longer gauge invariant, but it still remains canonically consistent and relativistic. Later, he went on extend these results to different non-abelian gauge theories in two and four dimensions, including (with Percacci) the chirally gauged Wess-Zumino-Witten model.
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