Chris Choi (최민영)

Wean Hall 8402

Hamerschlag Dr

Pittsburgh, PA 15213

I am a 2nd Year Ph.D. student in Physics at Carnegie Mellon University, working in theoretical cosmology under the supervision of Prof. Tina Kahniashvili. My research focuses on how gravitational waves can probe extensions of general relativity, such as massive gravity theories, and the early universe. I use pulsar timing array data to explore aspects of the stochastic gravitational wave background and the implications for Lorentz and parity violation.

Background

I received my B.S. in Physics from Carnegie Mellon University in 2024, where I developed an early interest in theoretical cosmology and gravity. I am originally from Seoul, South Korea, and grew up in New York City.

Outside Academia

Outside of research, I enjoy reading hard science fiction, drawing, climbing, weightlifting, and competitive speedcubing. I also have a deep interest in linguistics, in particular, the study of language families.

news

Dec 4, 2025	I am one of three speakers at the Astronomy on Tap event at Lolev Beer. I give a 15 min talk about a particular scene in a hard sci-fi novel, Diaspora, and how it connects to various topics in astrophysics.
Oct 16, 2025	I gave a 15 minute talk about my paper “Do Pulsar Timing Datasets Favor Massive Gravity?” at the COSMO 2025 Conference, hosted by my university CMU.
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!

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)}, }