I work on theoretical high energy physics and cosmology — the connection between the tiniest elementary particles and the entire universe. My main research interest is cosmic inflation, which describes the origin of the universe. A focus of my research involves extracting information about fundamental particle physics from the properties of inflation.

The great fun of doing research also drives me to explore other areas: gravitational waves, cosmic strings, eternal inflation, dark matter, dark energy, modified gravity, AdS/CFT and computer algebra.

A list of my papers can be found at INSPIRE, or HKUST library. See also the research group of Center for Fundamental Physics for related research at HKUST.

Signals from the universe played significant role for the development of particle physics. For example, the elementary particle “muon” was discovered in 1936 from cosmic rays. Afterwards, rapid progress of ground based collider experiments quickly took the leading role of studying particle physics since then. However, roughly speaking, the energy scale of new physics is distributed in logarithm scales, but the cost of building ground based colliders scales as a powerlaw with energy. As a result, we cannot rely on the ground based colliders forever for major particle physics discoveries.

Can cosmology return and help particle physics out of this situation?

A 5-min talk of this content is available here.

The expansion of the Universe is the cornerstone of modern cosmology. The evolution history of the Universe has been well measured from the first 3 minutes to 14 billion years.

However, what is the evolution history of the primordial universe, towards a tiny fraction of a second after the Universe was born? The Universe is likely to be exponentially expanding. But alternative theories show that the Universe may be contracting or nearly static.

How to distinguish those scenarios in a model-independent way?

Cosmology is a special type of science. In typical scientific research, one prepares an initial condition and measure the final outcome after an experiment. However, in cosmology, we do not have control of the initial conditions – they are prepared by Nature.

Especially, the structures in our Universe originates from the quantum fluctuations during the cosmic inflation. It is usually argued that “Bunch-Davies” states are the natural initial conditions of those quantum fluctuations. However, no precise statement has been proposed on how fast the inflationary fluctuations approach to Bunch-Davies after inflation starts, or after the inflationary process is disturbed by features in the potential. Also, the Bunch-Davies approach is not precise enough for nonlinear fluctuations.

How to determine the physical initial condition of inflationary fluctuations?

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