Beijing Institute of Mathematical Sciences and Applications

Hamed Adami , Chi Ming Chang , Mohammad Yavartanoo

Yuji Tachikawa

Thursday, April 28, 2022 10:00 AM - 11:00 AM

1131

Zoom 849 963 1368 (YMSC)

Superstring theory as we know it started from the discovery by Green and Schwarz in 1984 that the perturbative anomalies of heterotic strings miraculously cancel. But the cancellation of global anomalies of heterotic strings remained an open problem for a long time. In this talk, I would like to report how this issue was finally resolved last year, by combining two developments outside of string theory. Namely, on one hand, the study of topological phases in condensed matter theory has led to our vastly improved understanding of the general form of global anomalies. On the other hand, the study of topological modular forms in algebraic topology allows us to constrain the data of heterotic worldsheet theories greatly, as far as their contributions to the anomalies are concerned. Putting them together, it is possible to show that global anomalies of heterotic strings are always absent.

Yūji Tachikawa (立川裕二) is a Japanese theoretical physicist who studies supersymmetric field theories. He is a professor at IPMU, University of Tokyo. Tachikawa received his master's degree (Seiberg-Witten theory and instanton counting) in 2004, his PhD with Tohru Eguchi at the University of Tokyo in 2006 and was a post-doctoral fellow with Nathan Seiberg at the Institute for Advanced Study until 2011. In 2012 he became an assistant professor at the Kavli Institute for the Physics and Mathematics of the Universe (IPMU) at the University of Tokyo and shortly thereafter an associate professor at the Elementary Particle Theory Group at the University of Tokyo. He deals with supersymmetric string theories and gauge theories in different dimensions and with different numbers of supersymmetric charges and found new connections between the theories (duality). In 2010 he found with Davide Gaiotto and Luis Alday that six-dimensional N=(2,0) superconformal field theories that are compactified on a surface result in a four-dimensional gauge theory that has an AGT correspondence named after the authors with a simple conformal field theory (Liouville field theory) on the surface. For 2016 he received the New Horizons in Physics Prize. He is an invited speaker at the ICM 2018 (On Categories of Quantum Field Theories).