Interactions of Particles, Fields, and Strings

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This award funds the research activities of Professor Cumrun Vafa at Harvard University. The gravitational force is a key cornerstone of physics. Yet, when combined with quantum mechanics (the theory that governs the physics of the subatomic world), gravitational interactions lead to many puzzles. These puzzles are ultimately resolved within string theory, as a result of which string theory is perhaps the leading candidate for unifying gravity with quantum physics. One consequence of this resolution is that many possible particles and forces that could have existed in principle (and thus be part of the string-theory "landscape" of self-consistent theories) actually turn out to be forbidden (and thus are considered to belong to the so-called "swampland"). As part of this research, Professor Vafa will attempt to demystify the reasons why some theories belong to the swampland and not the landscape. The results of this research will therefore lead to a deeper understanding of how gravity works. As such, research in this area advances the national interest by promoting progress in fundamental aspects of science. This research is also envisioned to have significant broader impacts. Professor Vafa plans to continue his freshman seminar course, "Physics, Math and Puzzles", by teaching it once a year. This course aims to showcase deep principles of physics through simple mathematical puzzles. Professor Vafa also plans to give public lectures on these topics (based on a book he has just published). Moreover, Professor Vafa plans to continue running the Simons Center for Geometry and Physics summer workshops at Stony Brook University. These workshops will therefore continue to have a deep impact in educating some of the best young minds interested in theoretical physics, especially in questions related to string theory and the nearby areas of condensed-matter physics and mathematics. Professor Vafa also plans to continue delivering and participating in public forums to inform the public of progress being made in string theory and how it impacts our understanding of our universe.More technically, Professor Vafa will focus on elaborating the principles of the swampland and their connection to basic principles of quantum gravity, such as black-hole physics and unitarity. He will focus on drawing lessons from the supersymmetric examples of string compactifications, such as Calabi-Yau manifolds, where the most analytic control exists. A central aim for this research will be to explain why there is an upper bound on the number of massless particles we can get in supergravity theories, as well as the types of gauge forces and matter content we can obtain in a consistent theory of quantum gravity. These lessons will shed light on the case which is most relevant to our universe, namely the non-supersymmetric theories.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.