Born and raised in Hong Kong, I obtained my BSc in Physics with first-class honours in 2014 from The Hong Kong University of Science and Technology. I then earned my PhD in Physics in 2021 from New York University, specialised in the theoretical aspects of lower-dimensional physics. My doctoral thesis, supervised by Professor Massimo Porrati, was titled 'Chern-Simons Theory beyond Topology— Partition Functions on Manifolds with Boundary'. After getting my PhD, I briefly performed postdoctoral research at the University of Kentucky on topics such as quantum chaos and three-dimensional quantum gravity. I also gave invited talks to both international experts, as well as diverse general audience.
It has been conjectured that pure gravity without matter content, in three-dimensional spacetime with a negative cosmological constant, could be a complete quantum theory. One check is to compute its thermodynamic partition function as a Feynman path integral, which contains information such as the energy spectrum. The theory is also known, at least classically and perturbatively, to admit an equivalent description by a topological field theory called Chern-Simons theory.
In the work arXiv:1903.05100 [hep-th] done with my thesis adviser Professor Massimo Porrati, we performed the first direct computation of Chern-Simons path integrals on a class (the solid torus) of physical three-dimensional spacetimes. Among other things, we discovered subtleties in analytical continuations in the computations, and gave a prescription that produces the gravity partition function. Our work also found applications to subsequent works by other authors on certain other gravity theories that are conjectured to correspond to ensemble averages of conformal field theories.
Computing partition functions of candidate gravity theories defined on three-dimensional spaces that are handlebodies of arbitrary genus (think of bagels and pretzels) can tell us a lot about their quantum nature, or lack thereof.
In the work arXiv:2104.12799 [hep-th] done with my thesis adviser Professor Massimo Porrati, we computed Chern-Simons partition functions using radial quantisation on such spaces. We sliced the space along into constant-radius two dimensional surfaces, the same way we slice an onion. In this picture, the partition functions are transition amplitudes between states defined on the singular initial surface and the final surface. We found that a Wilson loop, which is the spacetime trajectory of a charged particle, shifts the holonomy of the initial state. Together with an appropriate choice of normalization, this procedure selects a unique quantum mechanical state on the constant-radius surface. Radial quantization allowed us to find the partition functions of Abelian Chern-Simons theories for handlebodies of arbitrary genus. For non-Abelian compact gauge groups, we showed that our method reproduces the known partition function on the solid torus.
It is a well-known fact that electric field can decay quantum mechanically by spontaneously producing a pair of charged particles, e.g. electron+positron.
In arXiv:2107.04561 [hep-th], in collaboration with Professor Matt Kleban and his student Hu, Xu-Yao, we studied quantum electrodynamics with massive fermions on a circle, in two spacetime dimensions. We discovered novel, previously unknown ways in which electric field decays without producing a charged pair. We performed a thorough investigation using both analytical approaches— bosonisation and the worldline formalism of field theory— and numerical lattice simulations. We made quantitative predictions of observables, in particular the decay rates and splitting of energy levels, from these different approaches, and found that they were in good agreement. Our work also settled some disputes in some parts of the literature.
A full list of my publications is available at InspireHEP, or Google Scholar.
*Note: authorships are sorted in alphabetical order of last names, as is conventional in high-energy physics.Electric Field Decay Without Pair Production: Lattice, Bosonization and Novel Worldline Instantons
Xu-Yao Hu, Matthew Kleban and Cedric Yu
JHEP 03 (2022) 197, arXiv:2107.04561 [hep-th]
Chern-Simons Theory beyond Topology: Partition Functions on Manifolds with Boundary
Cedric Yu
Partition Functions of Chern-Simons Theory on Handlebodies by Radial Quantization
Massimo Porrati and Cedric Yu
JHEP 07 (2021) 194, arXiv:2104.12799 [hep-th]
Kac-Moody and Virasoro Characters from the Perturbative Chern-Simons Path Integral
Massimo Porrati and Cedric Yu
JHEP 05 (2019) 083, arXiv:1903.05100 [hep-th]
Notes on Relevant, Irrelevant, Marginal and Extremal Double Trace Perturbations.
Massimo Porrati and Cedric Yu
JHEP 11 (2016) 040, arXiv:1609.00353 [hep-th]
I received the Outstanding Graduate Student Instructor Award in 2020 from the Physics Department of New York University.
As a teaching assistant for four years at New York University, I received positive acclaim from students and colleagues, for my clear, effective communication, as well as my commitment to high teaching quality.
Moreover, I:
substantially contributed to students’ developing a deep understanding in advanced graduate course materials (Quantum Field Theory and electromagnetism),
fostered intellectual growth in freshmen by guiding them in the use of the scientific method, formulating well-defined questions, building intuition on abstract notions, and the use of analytical thinking,
raised class performance by accommodating teaching to students of diverse educational backgrounds,
resolved students’ crises by providing pastoral support and being a keen listener of their opinions and needs.
Pedagogical notes are available upon request.