Chris Choi (최민영)

email: minyeonc@andrew.cmu.edu

Pittsburgh, Pennsylvania

I am a 1st-year PhD student studying Physics at Carnegie Mellon University, specifically the field of Theoretical Cosmology. I graduated from CMU with a Bachelors of Science in Physics and a minor in Math in 2024. I am currently advised by Prof. Tina Kahniashvili.

Background

I am originally from South Korea, and grew up mostly in Queens, NYC. My parents are from Jeollabuk-do, but I myself was born in Seoul. We moved to Los Angeles when I was about 7 months old, and then to NYC when I was around 5. Since 2020, I have been living in Pittsburgh, PA.

General Interests

I enjoy reading hard sci-fi novels and short stories, such as those by Greg Egan, Liu Cixin, and Peter Watts. You can check out my Goodreads account, where I update my catalogue and occasionally post reviews about sci-fi novels. I also love listening to music, especially the genre of prog rock and prog metal (about a 70%-30% split respectively). Specifically, I really enjoy retro prog rock from Sweden, with bands such as Moon Safari, A.C.T., Kaipa, Karmakanic, The Flower Kings, and Brighteye Brison. I also enjoy consuming anime in my free time, you can check out my MAL account. I am also competitive speedcuber, with a focus on the Face-Turning Octahedron. I also enjoy drawing in my spare time. My portfolio can be found on my art instagram. I also enjoy recreationally climbing, doing calisthenics, and weightlifting. Another passion of mine is the study of linguistics. I am endlessly fascinated learning about the various language families across the globe and how they are all related (or not related, in the case of language isolates).

Research Interests

My research explores how we can utilize the theory of gravitational waves to explore and constrain theoretical cosmology models, particularly massive gravity. I also utilize pulsar timing array data to gain information about the gravitational wave background, and potentially explain it with new theories of cosmology and gravity. In the recent past, my group used a time-dependent model of massive gravity, specifically one known as the minimal theory of massive gravity, to explain the stochastic gravitational wave background detected by NANOGrav in their 15-year dataset. There is a possibility that its source is of cosmological origin, because the astrophysical explanation falls short of being able to explain the background. I am also interested in the ways gravitational waves can be altered by free-streaming neutrinos, something I previously investigated. We explored the possibility of establishing a particular damping amplitude and comparing the results with previous work. Currently, I am working on analyzing the additional polarization modes from massive gravity and how it modifies the overlap reduction function.

news

Jul 2, 2025	My second paper, on comparing the pulsar correlations predicted by massive gravity with a few pulsar timing array datasets, has been submitted to arXiv [2507.02059].
May 20, 2025	I gave my first conference talk at the 2025 Phenomenology Symposium at the University of Pittsburgh.
Aug 13, 2024	My paper on the stochastic gravitational wave background in the view of massive gravity is finally accepted for publication in Phys. Rev. D!
Apr 15, 2024	I have accepted my offer to attend Carnegie Mellon University for a PhD in Physics! I will be continuing to work with Dr. Tina Kahniashvili.
Apr 11, 2024	I am awarded the ARCS Foundation Scholarship for my first 3 years of my PhD at CMU.

latest posts

Jul 14, 2025	Rebuttal to Tingman's Video
Jul 26, 2024	FTO Kinchranks
Apr 26, 2024	my favorite vegan restaurants

selected publications

arXiv
Do Pulsar Timing Datasets Favor Massive Gravity?

Chris Choi, and Tina Kahniashvili

Jul 2025

Abs arXiv PDF Bib Code Poster Slides

Several observational phenomena suggest that the standard model of cosmology and particle physics requires revision. To address this, we consider the extension of general relativity known as massive gravity (MG). In this Letter, we explore the imprints of MG on the propagation of gravitational waves (GWs): their modified dispersion relation and their additional (two vector and one scalar) polarization modes on the stochastic GW background (SGWB) detected by pulsar timing arrays (PTAs). We analyze the effects of massive GWs on the Hellings- Downs curve induced by modification of the overlap reduction function. Our study consists of analyzing observational data from the NANOGrav 15-year dataset and the Chinese PTA Data Release I, and is independent of the origin of the SGWB (astrophysical or cosmological). By considering the bound on the graviton mass imposed through the dispersion relation, we scrutinize the possibility of detecting traces of MG in the PTA observational data. We find that massive GWs predict better fits for the observed pulsar correlations. Future PTA missions with more precise data will hopefully be able to detect the GW additional polarization modes and might be effectively used to constrain the graviton mass.
@article{Choi:2025rfr, author = {Choi, Chris and Kahniashvili, Tina}, title = {{Do Pulsar Timing Datasets Favor Massive Gravity?}}, eprint = {2507.02059}, archiveprefix = {arXiv}, primaryclass = {astro-ph.CO}, month = jul, year = {2025}, keywords = {General relativity (GR) and modified gravity (MG), Gravitational waves (GWs) theory & observations}, url = {https://inspirehep.net/literature/2941986}, }
Phys. Rev. D
Stochastic gravitational wave background detection using NANOGrav 15-year data set in the context of massive gravity

Chris Choi, Jacob Magallanes, Murman Gurgenidze, and Tina Kahniashvili

Phys. Rev. D, Jul 2024

Abs arXiv PDF Bib Blog Code Poster

Convincing evidence of a stochastic gravitational wave (GW) background has been found by the NANOGrav Collaboration in the 15-year data set. From this signal, we can evaluate the possibility of its source being from the early Universe through the tensor perturbations induced by a massive spin-2 graviton field. We consider a time-dependent model of the minimal theory of massive gravity and find values of the graviton mass, mass cutoff time, and Hubble rate of inflation that amplify the energy spectra of primordial GWs sufficiently to reproduce the signal from the NANOGrav data within 1-3 standard deviation. However, a suppression mechanism for high-frequency modes must be introduced to conservatively obey the big bang nucleosynthesis (BBN) bound. While there are regions of the parameter space that reproduce the signal, it remains a challenge to simultaneously respect the BBN and cosmic microwave background bounds without making the graviton mass cutoff time too deep into the matter-dominated era.
@article{Choi:2023tun, author = {Choi, Chris and Magallanes, Jacob and Gurgenidze, Murman and Kahniashvili, Tina}, title = {{Stochastic gravitational wave background detection using NANOGrav 15-year data set in the context of massive gravity}}, eprint = {2312.03932}, archiveprefix = {arXiv}, primaryclass = {astro-ph.CO}, doi = {10.1103/PhysRevD.110.063525}, journal = {Phys. Rev. D}, volume = {110}, number = {6}, pages = {063525}, year = {2024}, keywords = {Big-bang-nucleosynthesis (BBN), Cosmic microwave background (CMB), Gravitational waves (GWs) theory & observations, Inflation, Perturbations,General relativity (GR) and modified gravity (MG)}, }