1. CERN Courier

2. Symmetry Magazine

1. New fundamental interactions

2. Dark matter

3. Dark energy

4. Neutrino oscillations

5. Light new particles (such as dark photon, axion)

6. Reformulating Quantum Field Theory using modern mathematics

My major research interests are in the fundamental interactions in Nature. Before I came to KAIST, I studied mostly new gauge interactions as the physics beyond the Standard Model. (See 5 mysteries the SM cannot explain.) Now, I am expanding my research topics to the strong interaction of the Standard Model and the gravitational interaction as well.

New Interactions:

Interaction is what governs the motion of things, and understanding the fundamental interactions in Nature is of utmost importance. A new gauge interaction might be crucial in understanding the dark matter sector of the Universe. Since we do not know where this new fundamental force is hidden or what it couples to, a proper investigation requires studying broad areas of the particle physics.

The Standard Model can explain only about 5% of the total Universe energy, and the bigger parts need something called dark matter and dark energy. In general, it is the interaction that distinguishes one particle from the other. (An electron has an electromagnetic interaction; a quark has a strong interaction; a neutrino has a weak interaction). It is quite possible that the dark matter might have its own interaction (dark force), and most of my research has been in this field. Recently, the focus of the dark matter research is moving to the possibility of significantly lighter candidates (compared to the traditionally popular TeV-scale ones), and I have been involved in this effort. (See the Light Dark World International Forum page.)

The dark energy is the biggest mystery in the Universe. Its nature could be a dark energy field that can evolve during the history of the Universe.  It is interesting to investigate if the dark energy field is under a new gauge symmetry. (See our model, which introduced the gauge symmetry in the dark energy sector. )

The neutrino is the least studied matter in the Standard Model due to its rather weak interaction (mediated by W and Z bosons). As the high-energy collider (such as LHC) experiments pass their peak time, the flagship particle physics experiments are moving (or at least expanding) to the long baseline neutrino oscillation experiments (such as DUNE and T2HK). There are certain kinds of new interactions that can be most sensitive to the neutrino oscillation physics, and this is one of my important research topics.

Strong Interaction:

I am also interested in the formal aspects of the strong interaction (Quantum Chromodynamics) in the Standard Model, which is well-known but still mysterious because of its non-perturbative nature. Because the strong interaction is too strong, the perturbative method (which played an important role in the great success of Quantum Electrodynamics) may not work best. I am trying to apply modern mathematics (developed after the Standard Model was devised) to describe the QCD in a more efficient way providing a significantly better calculation power.

Gravity:

Recently, I also got interested in the effort of finding the renormalizable quantum gravity. The quantum gravity is something all physicists have been dreaming of since the birth of the modern physics (that is the quantum mechanics and general relativity), yet there has been no true success. The main reason is because the interaction mediated by the graviton (of spin 2) is not calculable in the quantum field theory due to the nonrenormalizability of gravity. (See also this article.) The conformal symmetry approach may have a potential to make a breakthrough in this aspect, and I plan to launch a serious study in this direction. See 'tHooft's recent talk.