Krishna Rajagopal is the William A. M. Burden Professor of Physics at MIT. His research goals include probing the microstructure and phase diagram of hot QCD matter, the primordial liquid.
Professor Rajagopal enjoys thinking about QCD at high temperature and/or density, where various phases of matter in which the quarks and gluons do not coalesce into hadrons or nuclei are found, because understanding these liquids requires linking usually disparate strands of theoretical physics including particle and nuclear physics, cosmology, astrophysics, condensed matter physics and string theory. Heavy ion collision experiments at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) recreate droplets of the hot quark-gluon soup that filled the microseconds-old universe; these collisions are little bangs that recapitulate the big bang. They show that quark-gluon soup is a strongly coupled liquid, making it the earliest, and in a sense the simplest, complex form of matter. Understanding the properties of this phase of matter and how it emerges from QCD is a central challenge for the coming decade. Professor Rajagopal is incorporating insights obtained via gauge/string duality, perturbative QCD calculations, and hydrodynamics in modeling how jets produced in heavy ion collisions are modified via their passage through liquid quark-gluon plasma and how the wakes they leave behind in the droplet of liquid relax and evolve, discerning the most effective ways to use measurements of jets to probe the microscopic structure of this primordial liquid and understand how it forms and hydrodynamizes as remarkably quickly as it does. The longer term challenge is to use the data to learn how a strongly coupled liquid which shows no signs of the individual particles of which it is made can emerge from QCD, a quest which resonates with challenges that are central to contemporary condensed matter physics which asks how a complex world emerges from simple underlying laws.
Professor Rajagopal has also analyzed the critical point in the QCD phase diagram and the interplay of hydrodynamics and fluctuations near it. He has proposed signatures for its experimental detection, showing how to use data anticipated from the recently completed collision-energy scan at RHIC to search for the critical point in a large region of the QCD phase diagram. He also described the properties of the superfluid, color superconducting, quark matter that may lie at the centers of neutron stars, providing a clear understanding of the properties of matter at extraordinarily high densities. His work showed that cold quark matter at the highest densities is the QCD analogue of a superconductor but that if you could look at it using ordinary light it would look like a transparent insulator.
After growing up in Toronto, Professor Rajagopal did his undergraduate work at Queen’s University in Kingston, Canada. He obtained his doctorate at Princeton University in 1993 and spent three years at Harvard as a Junior Fellow. He then spent one year at Caltech before coming to MIT in 1997. At MIT, he served as the associate head of the Department of Physics from 2009 to 2015, stewarding the department’s undergraduate and graduate educational programs and helping to launch its early digital learning activities that improved the on-campus teaching of freshman physics and junior lab as well as its first MOOCs on quantum mechanics and quantum field theory. He served as the Chair of the MIT Faculty from 2015 to 2017 and as MIT's Dean for Digital Learning from 2017 to 2021. In that role, he led efforts to empower and catalyze MIT faculty as they use digital technologies to augment and transform how they teach students at MIT and, via open online courses and MIT's OpenCourseWare, to share the best of MIT knowledge and perspectives with learners around the globe. He is a Margaret MacVicar Faculty Fellow, and has won the Everett Moore Baker Award for Excellence in Undergraduate Teaching, the Buechner Prize for Excellence in Teaching, the Outstanding UROP Faculty Mentor Award, and the Buechner Award for Undergraduate Advising.