Dark matter theory and phenomenology

Ordinary matter constitutes a mere 16% of total matter in our universe, with the remaining 84% designated as dark matter. I seek to unveil the nature of dark matter by using the tools of cosmology, astrophysics and particle physics. Some key questions I would like to address include:

  • How does dark matter form, evolve and finally lead to our present-day universe?
  • How does dark matter interact with itself, ordinary matter and gravity?
  • How to detect it?

To help answer these questions, I developed effective field theory and studied the interaction of dark matter via nontopological solitons, neutron stars, structure formation, gravitational waves, etc. Some of the techniques developed during my research can also be used for other areas such as axions and modified gravity.

You can find my most recent publications at my INSPIRE profile.

Physics of solitons

The existence of solitons—stable, long-lived, and localized field configurations—is a generic prediction in many important physical scenarios, such as cosmic inflation and ultralight dark matter. They are also excellent targets for exploring the mathematical aspects of nonlinear dynamics. My research aims to understand:

  • The nonlinear properties of a single soliton, including stability, decay rates, polarization/macroscopic spin, quantum effects, general relativity effects, etc.
  • The interactions between solitons and their surrounding environments.
  • Applications of solitons in physics.

I develop the Mathematica package “DMSolitonFinder” that solves dark matter solitons in an automated way. It will dynamically change the boundary conditions of fields and the spatial range of the solutions until localized solutions are found under the requested precision and accuracy.

Here are some “photos” of vector solitons from 3+1-dimensional simulations [arXiv:2111.08700]:

Picture Picture Picture

Extremely polarized (left two) and hedgehog (right) vector solitons. Arrows stand for the magnitude and direction of the spatial part of a Lorentz 4-vector field, and the background color represents its energy density. In the nonrelativistic limit, the average particle spin in linearly polarized (left) and hedgehog (right) solitons is 0 while it is 1 in circularly polarized configurations (middle).

Probing new physics with compact objects

Terrestrial experiments have been very successful in establishing modern physics, but uncovering new physics at high energy scales poses a significant challenge. Complementing these efforts, astrophysical compact objects, such as white dwarfs, neutron stars and black holes, serve as powerful natural labs for probing new physics. These objects are dense and ubiquitous in the universe, often accompanied by extreme conditions like very high temperatures and intense magnetic fields. My research explores how these extreme conditions affect matter and fundamental forces, aiming to discover potential signals that can reveal new physics.

Here are a few of my research notes: