Well known and widely beloved theoretical physicist, Sandip Pakvasa, Professor for 46 years at the University of Hawaii, passed away in Honolulu on 24 September, 2020 from complications due to a head injury resulting from a fall.

Born in Bhavnagar, India, on 24 December, 1935, Sandip grew up in Mumbai. After completing his Master’s degree, Sandip came to the USA for his doctoral studies which he completed at Purdue University under the supervision of S. Peter Rosen. After a post-doc at Syracuse University, Sandip arrived in Hawaii in 1967 for a “temporary appointment” in the recently formed particle theory group, and remained there until his retirement in 2013. Even after this, he remained intellectually active, continuing his research activity and participating in Department colloquia and seminars as well as discussions with colleagues until the covid pandemic put an end to most in-person activities at the university.

Sandip was internationally recognized for incisive contributions to neutrino physics and to the physics of flavour and CP violation. He was a phenomenologist in the true sense of the word, and always had an eye for connecting theoretical ideas to real-world experiments. With Raju Raghavan, he proposed the BOREX solar neutrino experiment: the on-going Borexino experiment in Gran Sasso is a direct result of their proposal. Sandip and Hirotaka Sugawara pioneered the phenomenological exploration of the bold (Nobel-prize winning) proposal by M. Kobayashi and T. Maskawa that the observed CP violation in the Standard Model might originate in the physical phase in quark mass matrix if there are three families, which we now know to be true. Together with Vernon Barger, Kerry Whisnant, and Roger Phillips, Sandip discovered that matter effects could resonantly change neutrino flavour, but missed the applicability of this idea to resonant conversion in the sun where the density indeed varies over a large range! With John Learned, Sandip pointed out the “double-bang” signature for very high energy tau neutrinos interacting with a nucleus via the charged current in a large neutrino detector such as IceCube: the first bang comes from the primary interaction, while the second one comes from the time-dilated decay of the tau. With various collaborators, Sandip stressed the importance of mixing in the charm meson sector for probing physics beyond the Standard Model. These examples illustrate the breadth and importance of Sandip’s research and at the same time show that Sandip always had his eye on testable consequences of theory.

Sandip was widely recognized for his deep and clear understanding of physics. He played an important role in selecting lecturers, many of whom went on to win the Nobel prize, for the very successful Hawai Topical Conferences. He was recognized with awards from the Japan Society of Promotion of Science and from the Humboldt Foundation. He lectured internationally, and regularly traveled to India where he was known to a several generations of sciences: the Indian physics community hosted a very fitting tribute to commemorate the role he had played in furthering high energy physics on the subcontinent. Sandip served as a mentor to younger colleagues in Hawaii and also in India. Many recall his wise, kind and generous friendship and counsel.

Sandip, who is survived by his wife Heide, loved literature, art, and music. He loved good food (Sandip’s publications — this one with his brother Nikhil — include Pakvasa curry and green chutney recipes in the Honolulu Star Bulletin!), good beer and talking story with his many friends. But physics was his life. In later years, he developed an interest in the history of physics: in particular on how new ideas came into being, and how these came to be accepted.

Sandip was very widely respected at the University of Hawaii, not only as a scientist but also as a teacher and as a person. We very much miss his presence, and know that he will be missed by friends and colleagues that he has influenced, here, in India, and indeed the world over.

John G. Learned
Xerxes Tata