Research

Galaxy formation and evolution

I use the Galacticus, a semi-analytical model (SAM) for galaxy formation and evolution to perform a series of simulation for the galaxy redshift survey of the Nancy Grace Roman Space Telescope. It predicts the number densities of emission line galaxies that Roman can observe, and the clustering signal which can be used to forecast the cosmological measurements from baryon accoustic oscillation and redshift space distortion. Zhai+2019a, Zhai+2020a

Galaxy clustering and large scale structure

I measure the clustering of luminous red galaxies (LRGs) at z~0.7 from the eBOSS survey and perform a halo occupation distributioin interpretation. The paper marks the first scientifc result from eBOSS program. Zhai+2017a

Due to the non-linearity of the evolution of dark matter, the clustering of galaxies at small scale is difficult to model. I construct an emulator for the correlation function for the BOSS-CMASS galaxies, as a part of the Aemulus Project. The simulation product of the project is open to public, including the N-body simulation result, the emulator for the halo mass function, halo bias function. The data and code for the emulator of galaxy correlation function are also open to public. Our modeling demonstrates the power of small scale galaxy clustering in measuring the linear growth of the structure Zhai+2019b. Currently we are applying this approach to the data from BOSS LOWZ and CMASS, the analysis will be done in the near future.

Dark energy and related

We propose and apply a new statistics in the evaluation for the models of dark energy and modified gravities, which are assumed to explain the current accelerated expansion of the universe Zhai+2017b. This p-value metric measures the probability of observing the current universe if the assumed model is the true cosmology. The meaning of this metric is straightforward: if the assumed model deviates significantly from the true cosmology, then there will be a low probability to observe a universe like the one we live in.

I also play around with different data sets to constrain the cosmological models and properties of dark energy, aiming at the examinations of potential systematics of different observations, as well as tests on the underlying theories of cosmology. One of the latest attemps is to use the state-of-the-art observational data to constrain the evolution of dark energy density in a model-independent way Zhai+2019c.

Others

I develop a new probe based on the weak lensing effect of Type Ia supernovae to constrain the cosmological parameters. Compared with the luminosity-redshift relation of SNe, the weak lensing effect is subdominant. However, our simulation for the Roman SNe program shows that this signal is potentially significant at high redshift. This makes the SNe a more powerful cosmological probe in both measuring the expansion of the universe, and measuring the clumpiness of the matter distribution. Zhai+2019d, Zhai+2020b

My other research activities can be found from my publication list.