Welcome to my research page! To briefly summarize, my research interests lie at the intersection of astroparticle physics, cosmology, and gravitational waves. In particular, I’m interested in the fascinating interplay between these topics as well as the implications they have on one another. You can find a list of my publications at the bottom of the page and also on my inspireHEP page.
Below are some of the research topics I’m interested in and some of the projects I’ve been working on throughout the course of my PhD and Master’s degrees. Please feel free to reach out if you had any questions/wanted to discuss more in detail.
The true nature of dark matter remains elusive. It’s not such a crazy idea to consider the possibility that what we call “dark matter” may not consist of only one particle, but rather made up of several particles in a complex dark sector. In some of these dark sectors, radiative processes allowed between dark particles can influence, and hence drastically modify, the formation and evolution of dark matter clusters on galactic and cosmological scales. I am particularly interested in studying these disspative dark sectors and their connection to cosmology and astrophysics.
With Melissa Diamond and Joe Bramante, I considered the effects of having mulitple cooling channels in our dark sector, which can lead to the formation of compact objects and sub-solar mass black holes – the latter of which would serve as smoking-gun signatures of novel physics beyond the standard picture of black hole formation. We found that the particle physics model is directly imprinted in the cooling rates, and that the landscape of compact objects varies significantly with the specific particle model we consider.
We (a group of researchers at Queen’s University – Melissa Diamond, Chris Cappiello, Qinrui Liu, Joe Bramante, Aaron Vincent, and myself) have shown how a simple dissipative dark sector at early times (before Big Bang Nucleosynthesis) could result in a population of dark compact objects (DarkCOs) and primordial black holes (PBHs), which could be forming as late as today! Along with the plethora of novel, exciting observable features, this dark sector could also be all of the dark matter, while having about 20% of the sector in DarkCOs or PBHs.
In this exciting era of multimessenger astronomy, gravitational waves (GWs) may be the key in answering some of the mysteries of our Universe. In particular, there seems to be a discrepancy between early Universe and late Universe measurements of the Hubble parameter $H_0$: the expansion rate of our Universe. Binary mergers of black holes/neutron stars, called standard sirens, can be used to infer values of cosmological parameters such as $H_0$. I am currently studying how one can use the fact that sirens and galaxies are both tracers of the underlying distribution of matter in our Universe to statistically infer cosmological parameters such as $H_0$ in a novel Poisson log-normal framework. In addition, I am also interested in how the distribution of sirens “trace out” the said matter distribution, as well as other astrophysical and cosmological properties.
While the inflationary paradigm is a hugely successful description of the very early Universe, for several reasons it is important to consider the possibility of other alternatives. One commonly considered alternative is a cosmological bounce, in which the Universe contracts from some initial state before expanding. However, these bounce models oftentimes are at risk of instabilities and other issues.
Together with Ghazal Geshnizjani, I investigated the first observable implications in the power spectrum for scalar and tensor modes for a cosmological bounce generated by Cuscuton gravity. In particular, we found that we can obtain power spectra that agree with observations in the Cosmic Microwave Background (CMB).
An updated list of publications can be found on my inspireHEP page. Note that all author listings are alphabetical, unless indicated with an asterisk (*) beside my name.
J. Bramante, M. Diamond, and J. L. Kim, The effect of multiple cooling channels on the formation of dark compact objects, JCAP 02 (2024) 002. [2309.13148].
J. L. Kim* and G. Geshnizjani, Spectrum of Cuscuton Bounce, JCAP 03 (2021) 104. [2010.06645].