My research interests lie at the interface of particle physics, cosmology, and astrophysics. The general scope of my research is on finding new theoretical models that explain some mysteries of the Universe, such as the identity of dark matter and the observed cosmological excess of ordinary matter over antimatter. I am particularly interested in how dark matter and matter-antimatter asymmetry arise in the early Universe. A key aspect is also bridging experimental searches and such new theories where new particles have very feeble interactions with the known particles in the Standard Model of particle physics.

Education

Ph.D., University of California, Berkeley, 2017

M.A., University of California, Berkeley, 2012

B.A., University of California, Berkeley, 2011

Honors and Awards

• University of Minnesota Postdoc Awards in Impactful Research, Honorable Mention, 2021
• Department of Energy Office of Science Graduate Student Research Award, 2016
• Outstanding Graduate Student Instructor Award, UC Berkeley, 2012
• Physics Departmental Citation, UC Berkeley, 2011
• Physics Commencement Speaker, UC Berkeley, 2011
• National Science Foundation Graduate Research Fellowship, 2011
• Barry M. Goldwater National Scholarship, Honorable Mention, 2010

Selected Publications

1. Gravitational Wave and CMB Probes of Axion Kination, R. T. Co, D. Dunsky, N. Fernandez, A. Ghalsasi, L. J. Hall, K. Harigaya, and J. Shelton [arXiv:2108.09299]
2. Lepto-Axiogenesis, R. T. Co, N. Fernandez, A. Ghalsasi, L. J. Hall, and K. Harigaya JHEP 03 (2021) 017 [arXiv:2006.05687]
3. Predictions for Axion Couplings from ALP Cogenesis, R. T. Co, L. J. Hall, and K. Harigaya JHEP 01 (2021) 172 [arXiv:2006.04809]
4. Axion Kinetic Misalignment and Parametric Resonance from Inflation, R. T. Co, L. J. Hall, K. Harigaya, K. A. Olive, S. Verner JCAP 08 (2020) 036 [arXiv:2004.00629]
5. Axion Kinetic Misalignment Mechanism, R. T. Co, L. J. Hall, and K. Harigaya Phys. Rev. Lett. 124, 251802 (2020) [arXiv:1910.14152]
6. Axiogenesis, R. T. Co and K. Harigaya Phys. Rev. Lett. 124, 111602 (2020) selected for Editors’ Suggestion and featured in Physics [arXiv:1910.02080]
7. Dark Photon Dark Matter Produced by Axion Oscillations, R. T. Co, A. Pierce, Z. Zhang, and Y. Zhao Phys. Rev. D 99, 075002 (2019) [arXiv:1810.07196]
8. QCD Axion Dark Matter with a Small Decay Constant, R. T. Co, L. J. Hall, and K. Harigaya Phys. Rev. Lett. 120, 211602 (2018) selected as Editors’ Suggestion [arXiv:1711.10486]
9. Gravitino or Axino Dark Matter with Reheat Temperature as high as 10^16 GeV, R. T. Co, F. D’Eramo, and L. J. Hall JHEP 1703, 005 (2017) [arXiv:1611.05028]
10. SaxiGUTs and their Predictions, R. T. Co, F. D’Eramo, and L. J. Hall Phys. Rev. D 94, no. 7, 075001 (2016) [arXiv:1603.04439]
11. Freeze-In Dark Matter with Displaced Signatures at Colliders, R. T. Co, L. J. Hall, F. D’Eramo, and D. Pappadopulo JCAP 1512, no. 12, 024 (2015) [arXiv:1506.07532]