So-Young Pi

So-Young Pi

Professor until 2020
Emeritus (Professor Emeritus )
Office: PRB, Room 569. 617-353-4780


Research Interests:

Realization of Weyl (local conformal) Symmetry

In my current research I am pursuing topics concerning realization of symmetries when they arise in unexpected ways; for example, in models of cosmic inflation. Particularly intriguing is the possibility that Weyl symmetry is present, but the expected Noether charge and current vanish identically. My goal is to understand and clarify this unexpected realization of symmetry.

Selected Publications:

“Fake Conformal Symmetry in Conformal Cosmological Models” R. Jackiw and S.-Y. Pi, Phys. Rev. D91, 067501 (2015)

“Chiral Gauge Theory for Graphene” R. Jackiw and S.-Y Pi, Phys. Rev. Lett. 98, 266402 (2007)

“Inflation Without Tears” Phys. Rev. Lett. 52; 1725 (1984)

“Magnetic Monopoles in Grand Unified Theories” P. Langacker and S.-Y Pi, Phys. Rev. Lett 45, 1 (1982)

“Fluctuations in the New Inflationary Universe” A. Guth and S.-Y Pi, Phys. Rev. Lett. 49, 1110 (1982)

For a full list of publications, please see the attached CV.


  • Ph.D. in Physics, State University of New York at Stony Bro ok
  • B.S. in Physics, Seoul National University


  • Outstanding Junior Investigator Award, US Department of Energy (1986)
  • Fellow of American Physical Society

Research Descriptions:

The Big Bang, Dark Matter, and Cosmology

Many of the questions of current theoretical interest are beyond the energy reach of existing accelerators. However, extremely high energies were once realized in the largest natural particle accelerator, the Big Bang. Shortly after the Big Bang, the universe was composed of a hot plasma of elementary particles. The nature of this plasma, which depends on the properties of the constituent elementary particles, determined the subsequent evolution of the universe. By observing the universe today, we can obtain information about its state shortly after the Big Bang and obtain information about the interactions of these particles at high energy. Several cosmological problems are presently being considered, among them: Is there a consistent inflationary model of the early universe? What is the nature of "dark matter" and what role does it play in the development of large-scale structure? What mechanism produced the baryon excess in the universe?

Topological Effects in Quantum Field Theories

Topology, the mathematical description of the robustness of form, appears in many branches of physics and provides strong constraints on physical systems. Topologically interesting field theories predict various hypothetical objects and mathematical constructs. Although many of the fascinating objects have not been seen in particle physics, they demonstrate possible phenomena that quantum field theory can support. A significant deformation of the Dirac equation is achieved when the constant mass term is replaced by topologically non-trivial profiles. Examples of interesting profiles are: kink in one dimension, vortex in two and magnetic monopole in three. Dirac equation in the presence of such topological entities possesses an isolated zero-energy solution. The existence of zero-energy solution does not require a specific form for the inhomogeneous mass profile; all that matters is that it belongs to a non-trivial topological class. It has been shown that they give rise to fermion fractionalization and isolated Majorana fermion bound states depending on the absence or presence of superconductivity in the system. The difference between the two situations results in the presence or absence of a conserved fermion number.