Kalyana T. Mahanthappa

Kalyana T. Mahanthappa of Lincoln, Massachusetts, formerly of Boulder, Colorado, died peacefully on 2 November 2022. K. T., as he was known to friends and colleagues, was a theoretical particle physicist who worked on the standard model and physics beyond the standard model.

Born in Tumkur, Karnataka, India, on 1 May 1934, K. T. grew up in several towns as his family moved within the state to follow his father, a high-ranking civil servant. Showing an early aptitude for math and science, he completed a BSc with honors in physics from Mysore University (Bangalore) in 1954, followed by graduate studies at Delhi University. While working toward his MSc, somewhat on a whim, he thought to apply to graduate schools in the US. He completed one application, took it to the post office, and, stunned by the cost to mail it, decided to apply to only that one university. A few months later, he told his father he had been accepted to Harvard and insisted on going. K. T. was fortunate to have Julian Schwinger as his mentor and thesis advisor, and he was awarded a PhD in theoretical physics by Harvard in 1961.

His professional career spanned fellowships and faculty positions at UCLA, the University of Pennsylvania, the Institute for Advanced Study, and, from 1966 onward, the University of Colorado at Boulder, where he became full professor in 1970 until retirement in 2014. In addition, he had sabbatical fellowships at the Abdus Salam International Centre for Theoretical Physics, Cambridge University, and Imperial College London. He was elected a fellow of the American Physical Society in 1969.

K. T.'s enduring legacy is the Theoretical Advanced Study Institute (TASI) summer program, one of the outstanding summer intensive programs in the world for advanced graduate students doing particle theory. TASI was started in 1984 and originally moved from place to place. In 1986 the Scientific Advisory Board of TASI approached K. T. about hosting it permanently in Boulder. He agreed subject to the proviso that the scientific program would be solely the responsibility of a new set of organizers each year, while the local organization remained separate from the scientific organization and was handled by Boulder faculty. This division of labor is what keeps TASI fresh, and that is K. T.'s real educational legacy. TASI came to Boulder in 1989 and continues to be held there to this day. K. T. was the local organizer for 25 TASIs, from 1989 through 2013. He taught hundreds of undergraduates, trained and mentored more than 20 graduate students and postdoctoral fellows, and published more than 140 research papers in respected journals, conference proceedings, and book chapters.

His scientific career included many different aspects of theoretical physics. His earliest and most cited work developed the closed-time-path formalism, which describes the quantum mechanical evolution of systems in nonequilibrium states subject to time varying external fields. He then turned to studies of flavor symmetries in strong interaction physics. With the development of the standard model, K. T. looked at dynamical symmetry breaking, radiative symmetry breaking, and then grand unified models and supersymmetry. His work also extended to the interface between particle physics and cosmology, including work in 1980 on supercooling in SU(5) models of grand unification, contemporaneous with Alan Guth’s seminal paper on cosmic inflation, and widely cited work on implementing models for “natural” inflation using Coleman–Weinberg potentials generated by explicitly broken symmetries. These models demonstrated successful potentials that were stable under radiative corrections and showed the relationship between the underlying symmetry and cosmological observables such as fluctuations in the cosmic microwave background radiation.

In the later period of his career, K. T. investigated possible origins of neutrino masses, fermion mass hierarchy, flavor mixing, and CP violation. Among his many contributions was his work in 2009 where it was pointed out, for the first time, that CP violation can be entirely group theoretical in origin, due to complex Clebsch Gordon coefficients in certain non-Abelian finite groups. In his seminal paper in 2014, a classification of finite groups was found and the deep connection between physical CP violation and class-inverting outer automorphisms was elucidated. The symmetries of these models also give rise to interesting correlations between CP violation in neutrino oscillation and leptogenesis.

K. T. is survived by his wife of 61 years, Prameela, his three sons, and four grandchildren.

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