Cristian Joana’s Homepage

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This is Cristian Joana’s website. Welcome.

I am a theoretical and computational physicist specializing in early Universe cosmology. My research interests include inflation, primordial black holes, and gravitational waves from cosmological sources. I combine numerical relativity and analytical approaches to explore fundamental questions about the origin and evolution of the Universe.

I am currently transitioning to an Associate Professor position at Hainan University.

Previously, I was a postdoctoral fellow at the Institute of Theoretical Physics, Chinese Academy of Sciences (ITP-CAS), and most recently at ICTP-AP in Beijing. I have also been a visiting researcher at Institute of Science Tokyo in Ookayama/Tokyo and at the Universite Libre de Bruxelles (ULB) in Brussels. I obtained my PhD at the Universite Catholique de Louvain (UCLouvain) and my thesis focused on numerical relativity approaches to the early Universe, where I tackled the initial conditions problem of inflation and the process of parametric reheating.

You can check out my blog pages where I write summaries of some of my publications. From time to time I make video animations of my simulations, which can be found in here.

 

✨ New information will be released soon! Stay tuned for updates on the group, openings, and research directions at Hainan University.

 

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Research directions

Early Universe Phenomenology

I study the dynamics of the very early Universe, including models of cosmic inflation and reheating/preheating. My work aims to connect theoretical models with observable imprints, such as scalar and tensor perturbations, through both analytical tools and numerical simulations.

Formation of Compact Objects

I am particularly interested in the nonlinear dynamics that lead to the formation of exotic compact objects in the early Universe. This includes:

• Primordial black holes (PBHs)
• Oscillons and Q-balls
• Other nonperturbative phenomena arising in scalar field theories

These objects offer possible explanations for dark matter and probes into physics beyond the Standard Model.

Gravitational Waves from Cosmological Sources

I study gravitational wave (GW) backgrounds arising from early Universe phenomena, including:

• Second-order GWs induced by scalar perturbations
• GWs from first-order phase transitions
• Signals from oscillons and other nonperturbative structures

I am particularly interested in the potential detectability of these signals by current and future observatories such as LISA, ET, PTA, and advanced ground-based detectors.

Machine learning in Physics

Applications of Artificial Intelligence and Machine Learning methods alongside numerical simulations to study cosmological phenomena such as gravitational collapse thresholds and peak profiles generated during (stochastic) inflation.

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Interdisciplinary Research

In addition to cosmology, I have worked on dynamical quantum systems, particularly exciton-polaritons in condensed matter settings. My contributions include theoretical modeling of coupled light-matter systems with nonlinear interactions. See our paper for more detailed information.

I have also worked in the field of systems neuroscience, focusing on how the brain processes visual information. My collaborators and I used advanced statistical and machine learning techniques to match visual stimuli with neural responses in macaques under free-viewing conditions. Our publications can be found here and here. This research aims to uncover how the brain constructs a coherent visual experience from dynamic environments. I am not currenlty engenge in this line of research, but I always find it extremely intersting.

I have been also involved in some projects on Climate and Sustainability, providing (minor) support with data analyses.

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Collaborations