My research connects observational data and theoretical models to understand the fundamental properties of the Universe.
I analyze high-quality CMB observational data with novel analysis methods optimal for maximally extracting cosmological information, test the $\Lambda$CDM model and look for alternative cosmological models that can explain the observational results and tensions.
I was born and raised up in Xi'an, Shaanxi Province, China. I acquired my Bachelor of Science in Physics (Honors Program) at Xi'an Jiaotong University in 2018. I spent a year at the National Astronomical Observatory of China working with Prof. Gongbo Zhao, before moving to Davis for graduate school in 2019.
Outside of school, I like cooking, hiking, playing tennis and weightlifting.
Ge,Qu,Wang,Schaan,Wu,Friedland, 2026
Cosmological observations provide constraints on the sum of neutrino masses. Recent CMB and BAO data show a preference of a smaller (or even "negative") value of neutrino mass sum, compared to the minimum value allowed by neutrino oscillation experiments.
In this work, we implemented a coherent split of the neutrino mass sum based on its physical effects on cosmic geometry and structure growth.
We find a similar constraining power and "negative" preference on both geometry and structure growth channels.
Such a split can be a useful diagnostic to possible causes to the observed "negative" preference in the neutrino mass sum.
In a companion paper, we also derived the late-universe-free constraint on the neutrino mass sum, finding the combination of unlensed primary CMB and 4-pt lensing insensitive to late-time expansion history.
Optimal CMB Lensing
Ge et al. (SPT-3G Collaboration)
The deflection of CMB photons by the intervening gravitational potential is called CMB lensing. This is an important tool to map the mass distribution of the Universe. The reconstructed CMB lensing potential can also be used to undo the deflections, thereby cleaning out the lensing-induced B-mode signal that otherwise contaminates the primordial B-mode polarization signal.
I am a junior member of South Pole Telescope (SPT) collaboration, working on applying MUSE to optimally reconstruct the CMB lensing potential and estimate unlensed bandpowers simultaneously.
This new optimal method will be crucial for the analysis of future low-noise CMB maps, where the traditional Quadratic Estimator is less optimal.
"Cool" Atomic Dark Matter
Hughes, Ge et al. 2023
The "Atomic" Dark Matter (ADM) model consists of two massive dark fermions (a "dark proton'' and a "dark electron'') interacting with a massless dark photon. The massive dark fermions can be part or all of the dark matter, and the dark photon contributes to radiation in the Universe.
In this work, we found that the current BAO and Planck CMB data are still consistent with an ADM model prediction with BBN-predicted primordial helium abundance, which contains about 10% of the total DM being ADM and has the dark photon at low temperature.
The main constraining power on ADM models is from CMB lensing. Future CMB surveys, like SPT, Simons Observatory (SO) and CMB-S4, will be able to test the ADM model, if it is the cause of the S8 tension.
Constraints on Amount of Light Relics from CMB Observations
Ge, Cyr-Racine, Knox, 2023
We analytically discuss constraints on light relics from cosmic microwave background maps, using a family of scaling transformations that scale key rates in the evolution equations.
Besides the previously noticed causes of changing the photon scattering rate and the free-streaming species fraction, we identify two novel causes of changing the fraction of matter with pressure support and the recombination rates.
We use the Mirror World Dark Sector model as a reference model that admits a scaling transformation that increases light relic energy density while avoiding all of these causes.
Constraints on light relics in a given model can then be understood as due to the differences between the given model and the reference model.
Symmetry of Cosmological Observables, and a High Hubble Constant as an Indicator of a Mirror World Dark Sector
Cyr-Racine, Ge, Knox, 2021
We find that a uniform scaling of the gravitational free-fall rates and photon-electron scattering rate leaves most dimensionless cosmological observables nearly invariant.
A "mirror world" dark sector can exploit this invariance and resolve the Hubble tension, although only with a primordial helium abundance inconsistent with the amount inferred from the observations.
Talks
SPT-3G: Cosmology from CMB Lensing and Delensed EE Power Spectra Using 2019-2020 Polarization Data
Advancing Field-level and Simulation-based Inference for Cosmology
June/2026
SPT-3G: Cosmology from CMB Lensing and Delensed EE Power Spectra Using 2019-2020 Polarization Data
mm Universe 2025
June/2025
SPT-3G: Cosmology from CMB Lensing and Delensed EE Power Spectra Using 2019-2020 Polarization Data
15th Conference on the Intersections of Particle and Nuclear Physics
June/2025
SPT-3G: Cosmology from CMB Lensing and Delensed EE Power Spectra with 2019 and 2020 Polarization Data
American Physical Society Global Physics Summit 2025
March/2025
Atomic Dark Matter and Concordance of Cosmological Probes
CMB-S4 Summer Collaboration Meeting
July/2023
A Symmetry of Cosmological Observables, a Mirror World Dark Sector and the Hubble Constant Tension
