Research Interests

My research can be divided into two components. Currently, I am working on constraining elementary particle physics beyond the Standard Model (BSM) with astrophysical data, in light of new probes (gravitational wave, neutrino, 21cm signal, etc.). On the theoretical side, I also have strong interest in fundamental problems, such as the role of naturalness, history of the universe, quantum process, and in particular, the origin of the Standard Model (SM). I have done some work on noncommutative geometry and super connection, in order to constrain the left-right symmetric extensions of SM.

 

Constraining new physics with astrophysical probes (hep-ph)

With the detection of binary mergers, gravitational wave becomes a real physical probe that was not accessible before, a probe of the past of the universe, a probe of the far away ambient space, and more importantly, a probe of the dark sector. The first two points were studied extensively in the past few decades, while the third point is not immediately obvious for the following reasons. Because the recently detected gravitational wave signals are from binary mergers, it is nontrivial to map BSM, which is on the microscopic scale, to the macroscopic astrophysical objects. A natural question one should ask is therefore how the underlying BSM - if there is any -  affects the binary merger events. This is my main motivation of studying exotic gravitational wave sources. In this direction, I have studied the effects of hidden gauge sector on neutron star (NS) binary mergers (1711.02096), boson star on stochastic gravitational wave background (1802.08259), and boson star mass profile (in preparation). In short, gravitational wave signals provide us a probe that for the first time does not rely on the so called dark portal, an interaction term that links the dark sector to the visible sector purely for the sake of detectability.

In addition to gravitational wave signals, I am also looking into other astrophysical channels, such as the recent 21cm absorption signal, which can be easily washed out by BSM that changes the cosmic thermal history. As a more mature probe, astrophysical neutrinos can deliver phenomenal amount of information with the help of modern detectors, such as Borexino, SNO, Super-K/ Hyper-K, DUNE, JUNO, etc., just to name a few. With tons of data accumulated over the years, it is important to study whether there is a better channel to make use of it. In 1803.02835, I demonstrated that there is a cleaner neutrino channel for GUT monopoles, for it is mono-energetic and at higher energy compared to the pion decay channel used by Super-K. This leads to a better detection capability, if any fluctuation is seen, or tighter constraint otherwise.

 

Looking for BSM from alternative angle of perspective (hep-th)

The Standard Model has been tested for fifty years with undebatable evidence. However, it is not without puzzles, such as the role of naturalness for Higgs mass – although one can argue the same or it is even worse for cosmological constant, the origin of U(1) charge, the `accidental’ anomaly cancellation in SM, and the seeming arbitrariness of fermion masses. It is important for us to seek for new principles, or at least new perspectives, that might shed light on these fundamental puzzles.

As a practice (1804.0584), I have studied an alternative approach, non-commutative geometry, which generalizes K-theory to the non-commutative space. It provides a mathematically rigorous way to geometrize SM, in the similar fashion of treating gravity. My strategy for such exotic theories has two main characteristics: a) if it works, it is likely to provide a very different viewpoint toward things that we are very familiar with, such the construction of SM through gauge invariance. On the other hand, if it fails, it might reveal fundamental obstructions, such as reasons that prevent treating SM on the same footing as gravity. That would be equally important, if not more. b) When making assumptions, it is important to make small jumps so that the approach converges as it does in numerical integration. The second point was also valued by a lot of fellow scientists, such as the similar point made by t’Hooft at SM@50.  

In short, SM's validity in regards to various precision measurements of different processes and its robustness against any deformations remain unexplained. Attempts to reproduce and to justify the SM have been made in the past few decades. So far no concrete experimental evidence to prefer any models that extend the SM. Therefore, it is worth trying at both the phenomenological and theoretical end to reveal possible hints of new physics. We live in an exciting era of physics.