Jaiyul Yoo


Cosmology and early universe

I am primarily interested in theoretical astrophysics and cosmology, focusing on large-scale structure, cosmic microwave background, and inflationary models. My research aims at exploring the dark sector of the Universe and understanding the physical mechanism of perturbation generation in the early Universe. To explore the nature of dark energy, numerous large-scale galaxy surveys are ongoing or planned to be operational in a near future. These surveys will measure the positions and the shapes of millions of galaxies in the Universe with tremendous statistical power. However, precision measurements in these future surveys simultaneously bring in new challenges, demanding substantial advances in theoretical modeling and observational methods. 

In light of this recent development, I developed, for the first time, the fully relativistic version of galaxy clustering.
This work put the study of galaxy clustering on a sound theoretical footing for precision cosmology and opened a new area of research. The relativistic effect in galaxy clustering becomes substantial on very large scales, close to the horizon scales, in which dark energy models or alternative theories of modified gravity deviate from general relativity, and in which the fingerprint of the inflationary epoch remains in its pristine form. I investigate the subtle relativistic effect in galaxy clustering and develop theoretical models to test general relativity on large scales and probe signatures of the early Universe.

On small scales, where the measurement precision is highest, there exist different challenges in theoretical interpretation of the measurements --- nonlinear evolution and galaxy bias. I showed that the current power spectrum analysis will be biased by systematic errors in analyzing the redshift-space power spectrum measurements in future surveys. I apply newly developed methods to determine cosmological parameters from galaxy-galaxy lensing and galaxy clustering measurements of the SDSS data set. Furthermore, I refine the observational methods and tools designed for future galaxy surveys and perform a pilot study of its applications to SDSS measurements with ultimate goal of applying it to future surveys.



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