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The Chern-Simons (CS) theory -- a topological quantum field theory developed by Shiing-Shen Chern and James Simons -- is not only a breakthrough in the mathematical subject of differential geometry but also a major step in the characterization of physical systems like the quantum Hall. It provides a simple yet powerful description for the phenomena of charge-flux-attachment, fractional excitation and statistics in integer quantum Hall, fractional quantum Hall and various 2+1D topologically ordered quantum systems. In this talk, we present a generalization of the Chern-Simons theory to 3+1D by including an infinite number of components of the gauge field and find that they represent interesting new types of order in 3+1D. When the system is gapped, such infinite-CS theories fall into the category of 'fracton order', a phenomena discovered recently in exactly solvable lattice models where point-excitations either cannot move or are only allowed to move in a lower dimensional sub-manifold. The infinite-CS theories provide examples beyond what is possible in lattice models and greatly expand our understanding of the fracton phenomena. When the theory is gapless, it can represent a new type of stable gapless order in 3+1D with robust topological feature in the gapped sector. Bio: Xie Chen is a Professor of Theoretical Physics at the California Institute of Technology. Dr. Chen obtained her Ph.D. degree from MIT in 2012 and was a Miller research fellow at the University of California, Berkeley before joining Caltech in 2014. Dr. Chen is a condensed matter theorist studying emergent phenomena in strongly interacting quantum many-body systems. She received the New Horizons in Physics Prize from the Breakthrough Foundation in 2020. |
