Yun Wang


Associate Professor
B.S. 1985 Tsinghua Univ., P.R. China
M.S. 1987 Carnegie-Mellon
Ph.D. 1991 Carnegie-Mellon
Past Positions:
Postdoctoral Positions at
Univ. of Florida,
Fermilab Astrophysics Center,
Princeton University;
Visiting Assistant Professor at
Univ. of Notre Dame.

Hubble Deep Field South

RESEARCH DESCRIPTION

My research has focused on extracting fundamental physics from cosmological data, in particular, probing dark energy and early universe physics using supernovae (SNe), cosmic microwave background anisotropy (CMB), and cosmic large scale structure data.

I. Probing Dark Energy.
Dark energy, a mysterious energy component of the universe with negative pressure, has caused the observed acceleration of the expansion rate of the universe. Solving the mystery of the nature of dark energy is the most important problem in cosmology today. Dark energy can be probed using various techniques, most notably, using Type Ia supernovae (SNe Ia) as cosmological standard candles. I have done fundamental work in the use of supernovae to probe dark energy. My work has ranged from survey strategy, optimal data analysis, to the modeling of weak lensing effects.

Here is some of the work that I have done:

Survey Strategy: I did the feasibility study of a deep supernova survey on a dedicated telescope in 1998; the number of supernovae expected from such a survey surprised and encouraged many observers. In 2001, I studied the relative merits of a very deep survey of supernovae as compared to shallower wide-field surveys in placing constraints on dark energy. Based on this, I have developed a mission concept for the NASA-DOE Joint Dark Energy Mission (JDEM), Joint Efficient Dark-energy Investigation (JEDI), in collaboration with Arlin Crotts (Columbia) and Peter Garnavich (Notre Dame).

Extracting Dark Energy Constraints from Data: In a series of papers starting in 2001, I have shown the value in analyzing the dark energy density instead of (or in addition to) its equation of state. This is because the dark energy density is more closely related to observables (hence better constrained), and can also probe a greater range of dark energy models than the dark energy equation of state. I have also demonstrated the importance of making model-independent parametrizations of dark energy, and improving the robustness of the analysis by imposing priors from complementary observational data (such as cosmic microwave background and galaxy clustering) in a consistent manner (2001-2004). I have also worked on using weak lensing (2003), Lyman-alpha forest (2003), and galaxy clustering (2004) as complementary probes of dark energy. Wang & Tegmark (2004) gives the most up to date and accurate dark energy constraints from data. Wang & Tegmark (2005) presents a new robust data analysis technique and shows the potential of JEDI in measuring dark energy density.

Weak Lensing Systematic of Supernova Cosmology: I have shown how the weak lensing effect of supernovae can be analytically modeled by a universal probability density function derived from the matter power spectrum (2002). I set up a framework for removing or minimizing the effect of weak lensing of supernovae on cosmological constraints by flux-averaging (I have made my flux-averaging code available to the public on my website) (2000,2004). Most recently, I showed that weak lensing effects may have already begun to set in and must be dealt with in deriving robust constraints on dark energy (2005).