Research

Epoch of Reionization

The epoch of reionization (EoR) is usually associated with the formation of first stars and galaxies. The UV light from the first stars ionizes the intergalactic medium and the resulting free electrons leave signatures on quasar spectra, cosmic microwave background anisotropies, neutral hydrogen maps from 21 cm experiments, etc. Studies of reionization has not only implications for our astrophysical understanding of stellar and galaxy formation, but also impacts our interpretation of important cosmological parameters such as neutrino mass (for determining neutrino hierarchy) and dark energy.

Chen Heinrich’s work on reionization has focused on signatures of reionization in the CMB power spectra, by means of a principal component (PC) analysis. The PC analysis has advantages over conventional approaches by completely extracting all reionization signatures in the polarization data. See Chen Heinrich’s works on reionization.

Reionization

 

Inflation with Features

Inflation Potential

Inflation is a period of near-exponential expansion of space that stretched quantum fluctuations to macroscopic scales, seeding fluctuations in the energy density that we observe today in the cosmic microwave background (CMB) and the large scale structures (LSS).

Prof. Wayne Hu, Dr. Miranda, Dr. Motohashi and I have developed theoretical and numerical techniques for improving the accuracy of power spectrum predictions for the class of inflationary models with features in the inflaton potential. We found a universal template leading to much more accurate theory predictions and capturing all non-linear excitations in the inflaton field with a simple form. This non-linear template corrects bias of lower-order templates used in past searches of axion monodromy and will enable searches of potential features with higher amplitude and frequency. Learn more here.

 

Curvaton Model and Origin of Matter

Lensing Bias to CIP

A major part of my research has focused on doing simulations and forecasting works to design the best data analysis techniques for probing the curvaton model, a type of inflation model with an extra scalar field. In particular, with Prof. Daniel Grin and Wayne Hu, I developed and tested new techniques to improve the signal-to-noise of the curvaton signatures in the CMB and to remove bias effects from gravitational lensing. Measuring those signatures with CMB-Stage 4 will confirm or eliminate certain scenarios of the curvaton model in which baryon number or dark matter originates from the curvaton. See Chen He Heinrich’s work on the curvaton.