Rajaji, as he was affectionately called, was the first of 10 children born in 1936 in a small town, Kamuthi, near Madurai in Tamil Nadu. His parents had modest means (his father owned a shop selling brass vessels). He went to Kshatriya Nadar school in Kamuthi up to fourth standard and then to Board High School till eleventh standard. Throughout he had many excellant and inspiring teachers but his high school years were marked by an absence of teachers for Science. Rajaji was essentially self taught in Mathematics (only Arithmetic was taught in school). Nevertheless, he was at the top of the class all through his schooling. He went on to higher education, with encouragement from his father, though the family wanted him to continue in business.

Higher education was a problem due to lack of finances. Rajaji got a loan scholarship from the Nadar Mahajana Sangam and also the merit-cum-means scholarship of the Madras state government to pursue intermediate at The American College in Madurai in 1952. Here he experienced watching the night sky through the telescope. He read Eddington’s “Expanding Universe” and Gamow’s “Life and death of the Sun” in the well equipped library in the college. He wrote his first article “Mysterious universe” for the college magazine. By the end of intermediate in 1954, he had made his decision to pursue physics, having done very well in the exams.

Rajaji moved to Madras to pursue his undergraduate education at the Madras Christian College (MCC). Initially he was admitted to mathematics honours which he did not like but by sheer luck a seat opened in Physics honours which Rajaji took gladly. He was taught by an excellent faculty; he especially mentions M A Thangaraj, the only Ph.D among his teachers, fondly. While at the MCC he had the opportunity to meet many scientists from the Tata Institute of Fundamental Research (TIFR) who were conducting cosmic ray balloon experiments in the campus. Many of them – MGK Menon, Bernard Peters etc., – also gave lectures to students. Rajaji was inspired to apply for the Atomic Energy Establishment Training School (which later became the BARC training school) .

The training school was Homi Bhabha’s great idea to develop the human resources needed for the Atomic Energy program. The one-year program started in 1957 with about 150 students. Rajaji topped the first batch by a wide margin in 1958. He received a gold medal, much later, from Prime Minister Manmohan Singh during the golden jubilee of the training school in 2007. This allowed him to choose between TIFR or AEET (later called BARC). He chose to join TIFR to pursue his research in Theoretical Physics. The first three years, 1958-1961, in TIFR were spent diving deep into quantum mechanics, physics of hyper nuclei, and the quantum theory of radiation. An event that had an impact on his learning was the Bangalore Summer School in 1961 where Murray Gellmann and Richard Dalitz were the lecturers. The former talked about the “Eight-fold way” where proton, neutron and other baryons span an octet representation of the group SU(3). Rajaji remembers the persistent question from Dalitz about the fundamental representation of SU(3) which should have only three states. There was no answer from Gellmann. Rajaji felt that if he had answered, then the idea of quarks would have originated in Bangalore. Furthermore, if he or other participants had pondered over the question, it would have been a major Indian discovery and hence he considered it a missed opportunity.

As was the custom in TIFR in those days, and on the suggestion of MGK Menon, Rajaji was packed off in 1961 to do his PhD in the University of Chicago. He did his thesis work with Richard Dalitz at the University of Chicago while also attending the lectures by many luminaries of the department which included Fermi, Telegdi and Chandrasekhar. He spent a year at Oxford University before returning to TIFR in 1964. In fact when he returned to Bombay, he had not yet got his Ph.D – his defense was conducted by post after which University of Chicago awarded him the degree! Immediately after his return he married Suthandra Devi in 1965. His daughters Poongodhai and Uma were born in 1966 and 1972 respectively.

Rajaji moved to the University of Madras in 1976, primarily to be in a place with a large number of students as well as to be closer home to his roots though the immediate provocation was the anti-Madrasi sentiment growing in Bombay at that time. The university made every effort to match his emoluments at TIFR. The Department of Theoretical Physics was already a well established department with active faculty headed by P M Mathews. With the addition of Rajaji, the Department of Theoretical Physics at Madras University became one of the best places to do theoretical physics in India. This despite the fact that there was no additional funding for faculty beyond the bare salary unlike in TIFR where every conceivable facility was available. The department, which was a pure research department, also started an MSc course around this time. Rajaji brought a project “Gauge Theory” funded by the University Grants Commission (UGC) using which he created an active research group including many post-docs and students along with other faculty.

In 1983 the founder director of the Institute of Mathematical Sciences (IMSc), Alladi Ramakrishnan, retired. The Institute was small at that time when the Department of Atomic Energy stepped in to expand the activities of IMSc. In 1984 Rajaji was appointed as the Joint Director of the Institute vested with the full powers of the director when the newly appointed director, E C G Sudarshan, was not in station. He was initially reluctant to accept the offer but was persuaded by Raja Ramanna who was then the minister for Science and Technology. In the first five years Rajaji went about building a strong physics group, hiring a young group of researchers from Institutions all around the world. In order to attract good faculty, he also needed to improve the infrastructure. Through his efforts, the institute was granted the land across the street where the hostel and guest house now stands. The salary structure was not competitive. Rajaji worked to bring this on par with other research institutes in India. However, the power structure was not ideal and led to serious misunderstandings and problems with the Director. The resulting turbulence left a permanant scar in Rajaji’s mind as he faced the brunt of the problems in the late 80’s. Things soon normalised after R Ramachandran took over as the Director in 1990. Rajaji continued his research work in peace until his formal retirement in 2001 and beyond. He remained Professor Emeritus till his last day at IMSc.

The turbulent period of the late 80’s at IMSc also saw many faculty leaving the Institute. The distinguished mathematician, C S Seshadri who had helped grow the Mathematics and Computer Science groups at IMSc along with Rajaji, also left along with some of his proteges to found the new institute for Mathematics which later became Chennai Mathematical Institute (CMI). In the first decade of the millenium Rajaji helped Seshadri in creating a physics school at CMI. Along with R Balasubramanian he encouraged many of the IMSc faculty to teach at CMI in the beginning. The synergy created by Rajaji and Seshadri and others between IMSc and CMI continues to this day.

The closure of KGF underground laboratory was a set back for the pioneering cosmic ray experiments deep underground. Rajaji was one of those who strongly believed that this pioneering effort should be continued and revitalised. He strongly supported the proposal in 2000 to set up the India-based Neutrino Observatory (INO), which would house the world's most massive magnetised iron detector. Rajaji contributed to define the physics goals of such a detector, mainly through the study of naturally occurring atmospheric neutrinos. This would become his life’s mission in the last 25 years. In spite of his age and condition of health, Rajaji travelled widely, canvassing for the project with people from the scientific community, politicians, administrators and the general public. Rajaji was involved with the site selection, and worked vigorously for this very ambitious project, although unfortunately it has still not seen the light of day.

All through his life Rajaji has been an exemplary teacher who did not hesitate to teach at any level – from schools students to advanced researchers and teachers. His move from TIFR to the University of Madras reflected this attitude. The absence of graduate training programs in HEP was felt by all researchers and students in the 70s and 80s. To overcome this lacuna, the Department of Science and Technology started a two week long program of intense teaching of basics as well as recent advances in HEP beginning in the 80s. These schools came to be known as SERC schools.

N Mukunda took charge of these schools in the first five years followed by Rajaji in the next five years. He gave a course in almost all of these, highly successful, schools. These SERC-HEP schools continue to operate successfully to this day.

Rajaji lectured extensively about science, in particular about INO, in both English and Tamil. He started writing regularly in Tamil about science for a monthly magazine edited by Jeyapragasam from Madurai. Two volumes of his collected articles in Tamil has also been brought out. He was also the inspiration behind the “Sunday School”, started by S V M Satyanarayana, in which any student of physics could come and learn physics from stalwart teachers. Students came from all over Tamil Nadu, many of whom have become excellent researchers in their own right. This school celebrated twenty five years recently and still continues. Encouraged by the success of a similar effort in Mathematics, Rajaji encouraged the setting up of “Physics Training and Talent Search” (PTTS) to identify exceptionally talented physics students and train them towards research. Both these programs have achieved success in recent years.

Rajaji was active in research over six decades. He has significant contributions in a wide range of areas – hypernuclear physics, flavour physics, current algebra, neutral current weak interactions, integer quark model, string theory, new forms of quantum statistics, neutrino physics, dark matter, etc. He has published more than 200 research papers. He was always keen to enlarge his sphere of activity and influence over the development of High Energy Physics (HEP) in the country – a true scholar. We highlight some of his important contributions.

In the 60’s Rajaji and Dalitz showed that a multi-channel resonance pole is followed by retinue of poles on the complex Riemann sheets on the complex energy plane. This answered one of the serious objection of Oakes and Yang against SU(3) flavour symmetry, paving the way for the eventual success of SU(3) flavour symmetry. The core of his thesis was this discovery of what is now known as “Shadow Poles”. Following this, he worked on the structure of Lambda L(1405 MeV) which is an odd-parity excitation of the Lambda L(1115 MeV) baryon. The excitation energy is nearly 30% less than in the case of the nucleon odd-parity excitation and hence it was anomalous. Rajaji made the point that it could not be a 3-quark bound state and proposed that it should be a molecular bound state of hadrons – a nucleon and kaon. After nearly fifty years, this fact is getting confirmation from QCD lattice gauge theory calculations.

He was probably one of the first ones to see the tremendous potential of the Weinberg-Salam (W-S) model soon after it was proposed. The model, a precursor to the Standard Model (SM), described in a unified way the weak and electromagnetic interactions of particles. He gave a course of lectures on this electro-weak unified theory at many places. The lectures he gave at the Saha Institute of Nuclear Physics in 1971 were turned into lecture notes forming the basis for many an young researcher to learn the W-S model. This was the first such course in the country but probably also in the world. Many young physicists benefitted tremendously from these lectures. Though he was one of the first to get on to the Gauge Theory band-wagon, he could not make substantial contribution in the initial stages. One of Rajaji's regrets was that even though he had a "seat on the front row", he missed out on the “big stage”. But not for long!

As soon as the neutral current weak interaction, a prediction of W-S model, was discovered at CERN, Rajaji and K V L Sarma presented in 1975 the first model-independent analysis of the data analysing all the constraints. The “Master Equations” as Sakurai called them were central to the determination of neutral current coupling constants when combined with the work of Sakurai and L M Sehgal.

Around the same time, Rajaji and Probir Roy constructed a colour gauge theory with integrally charged quarks. They showed that quarks, even if integrally charged, can manifest as fractionally charged particles (which is what we now know them to be) in deep inelastic scattering experiments, a result that was also obtained by Jogesh Pati and Abdus Salam. He continued working on the integrally charged quark model well into the 80’s with his students T Jayaraman and Lakshmi Bala and collegue Saurabh Rindani. At that time the data seem to indicate that it could be a possibility but over time it became clear that was not the correct theory. While at the university, he also attempted an ambitious program of proving the quark confinement with his colleague V Srinivasan.

The decade of 80’s was somewhat dull by Rajaji’s standards since he was fully immersed in rebuilding IMSc. But he encouraged and directed some of us by pointing out important directions in high energy physics (HEP), especially neutrino physics where extraordinary results were being found and neutrino mixing and oscillations were discovered. This became a big program in the 90’s, when Rajaji along with Uma Sankar, Mohan Narayan and one of us (MVN) embarked on a complete analysis of all data on neutrino oscillations in a realistic three neutrino-flavour framework. Along with Uma Sankar and Mohan Narayan, he was the first to analyse the null result on neutrino oscillation for the CHOOZ reactor neutrino experiment using the three-flavour framework. The analysis gave an upper bound on one of the neutrino mixing angles. In the first preprint put out by CHOOZ, they had concluded wrongly that their result contradicts the atmospheric neutrino data since they had used only a two-flavour toy model. This was communicated to the experimenters who subsequently corrected their preprint – but without any acknowledgement or reference to the IMSc work! The three-flavour analysis of all phenomena continued into the new millenium including the day-night effect with solar neutrinos in collaboration with Rahul Sinha. The neutrino production from supernove and its possible signatures were analysed in collaboration with Indumathi and Murthy. As soon as the idea of INO came up, the sensitivity of the ICAL detector for its physics goals was analysed in collaboration with Indumathi, Murthy and Nita Sinha. With Earnest Ma of the University of California, he constructed the A4 model of neutrino masses and mixing which became quite popular due to its simplicity. In collaboration with M K Parida and R Mohapatra he worked on understanding the differences between neutrino mixing angles and quark mixing angles using the renormalisation group evolution.

While the neutrino work was going on in full steam, Rajaji was also involved in a completely different field – new forms of quantum statistics – with A K Misra, when there was a renewed interest in these digressions due to fractional statistics playing a role in understanding the Quantum Hall Effect. More recently he got involved in the discussions on Laser Plasma Acceleration (LPA) as he believed that the future of high energy accelerators lies with LPA.

Rajaji was also quite daring and did not hesitate to speculate or take risks on some important issues when required. Since he had already worked on the so-called anomalous Kolar events, when one of us (MVN) asked him if it could be due to dark matter decay, he immediately jumped at the possibility. He knew about these anomalous events since the late 80s and had even tried to explain it unsuccessfully. Within a few hours the details were worked out and the paper was written in a matter of couple of days. Even though it was later realised that the idea could cause problems elsewhere or may even be wrong, it still remains a tantalising possibility. But it highlights his ability and keenness to work on unconventional ideas.

Rajaji did his research, public outreach, institute building in a refreshingly lively, honest way. He was a generous, loving and kind-hearted person who would never say no when help was needed. In the passing away of Rajaji we have lost a colossus who touched the lives of a huge number of people – students, collaborators, friends and family. We will miss him, his boundless enthusiasm and his infinite optimism.

“Yathum Ooray, Yavarum Kelir” (All places are mine and all are my relatives)

– Kaniyan Poongunranar, around 6 BCE Sangam poetry.

Notes: 1. G Rajasekaran, My Inward Bound Journey, https://play.google.com/store/books/details?id=9h-CEAAAQBAJ (The tamil quotation at the end is taken from this autobiography) 2. This article is based on the tribute to Rajaji that appeared in the journal Current Science: https://www.currentscience.ac.in/Volumes/125/01/0087.pdf