Research

As an N3AS Fellow working at North Carolina State University and then UC San Diego, I have been studying other environments where flavor transformation of neutrinos play a potentially important role: dense astrophysical environments, such as core-collapse supernovae (CCSNe) and neutron star mergers (NSMs). More precisely, I have focused on “fast flavor oscillations”, which are instabilities occurring on timescales of nanoseconds and lengthscales of centimeters in a NSM. We have developed a framework to describe neutrino evolution in this context using only the first angular moments of neutrino distributions, a significant improvement to bridge the gap between local studies of neutrino flavor transformation and large-scale simulations.

My PhD at the Institut d'Astrophysique de Paris, under the supervision of Cyril Pitrou, was focused on the study of the evolution of neutrinos in the early Universe. During the very first minutes after the Big Bang, neutrinos and antineutrinos are part of a large array of events that shape the Universe evolution up until today. In the era of precision cosmology, producing accurate and reliable theoretical predictions of quantities which parametrize the neutrino “contributions” is thus necessary and within our reach.

I defended my thesis on June 10th, 2022 at the Institut d'Astrophysique de Paris in front of a jury composed of Marco Cirelli (chair), George Fuller (referee), Passquale Serpico (referee), Julien Lesgourgues (examiner), Mariam Tórtola (examiner) and Cyril Pitrou (supervisor). My PhD manuscript can be found on arXiv or theses.fr.

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List of publications

A complete and up-to-date list of publications can be found on Inspire-Hep.

  1. G. Barenboim, J. Froustey, C. Pitrou and H. Sanchis, Primordial neutrinos fade to gray: constraints from cosmological observables, [2504.07178].
  2. E. Grohs, S. Richers, J. Froustey, F. Foucart, J. Kneller and G. McLaughlin, Advection algorithms for quantum neutrino moment transport, Phys. Rev. D 111, 083018 (2025) [2501.07540].
  3. J. Kneller, J. Froustey, E. Grohs, F. Foucart, G. McLaughlin and S. Richers, Quantum Closures for Neutrino Moment Transport, Phys. Rev. D 111, 063046 (2025) [2410.00719].
  4. A. Suliga, P. Cheong, J. Froustey, G. Fuller, L. Gráf, K. Kehrer, O. Scholer and S. Shalgar, Non-conservation of Lepton Numbers in the Neutrino Sector Could Change the Prospects for Core Collapse Supernova Explosions, [2410.01080].
  5. J. Froustey, J. Kneller and G. McLaughlin, Quantum maximum entropy closure for small flavor coherence, Phys. Rev. D 111, 063022 (2025) [2409.05807].
  6. S. Richers, J. Froustey, S. Ghosh, F. Foucart and J. Gomez, Asymptotic-state prediction for fast flavor transformation in neutron star mergers, Phys. Rev. D 110, 103019 (2024) [2409.04405].
  7. Y. Liu, K. Yao, J. Hong, J. Froustey, Y. Shi, E. Rrapah, C. Iancu and G. Li, Ternary Tree Fermion-to-Qubit Mapping with Hamiltonian Aware Optimization, 2025 IEEE International Symposium on High Performance Computer Architecture (HPCA) [2409.02010].
  8. J. Froustey and C. Pitrou, Constraints on primordial lepton asymmetries with full neutrino transport, Phys. Rev. D 110, 103551 (2024) [2405.06509].
  9. J. Froustey et al., Neutrino flavor transformation with moments: application to fast flavor instabilities in neutron star mergers, PoS TAUP2023 341 (2024) 341, [2402.09274].
  10. J. Froustey, S. Richers, E. Grohs, S. Flynn, F. Foucart, J. Kneller and G. McLaughlin, Neutrino fast flavor oscillations with moments: linear stability analysis and application to neutron star mergers, Phys. Rev. D 109, 043046 (2024), [2311.11968].
  11. E. Grohs, S. Richers, S. Couch, F. Foucart, J. Froustey, J. Kneller and G. McLaughlin, Two-Moment Neutrino Flavor Transformation with applications to the Fast Flavor Instability in Neutron Star mergers, ApJ 963 11 (2024), [2309.00972].
  12. J. Froustey and C. Pitrou, Primordial neutrino asymmetry evolution with full mean-field effects and collisions, JCAP 03 (2022) 065, [2110.11889].
  13. J. Froustey, Precision calculation of neutrino evolution in the early Universe, J. Phys.: Conf. Ser. 2156 (2021) 3, 012013, [2110.11296].
  14. J. Froustey, C. Pitrou and M.C. Volpe, Neutrino decoupling including flavour oscillations and primordial nucleosynthesis, JCAP 12 (2020) 015, [2008.01074].
  15. J. Froustey and C. Pitrou, Incomplete neutrino decoupling effect on big bang nucleosynthesis, Phys. Rev. D 101, 043524 (2020), [1912.09378].

Outreach

  • Quelqes secondes après le Big Bang : sus aux neutrinos, Le Rayon (site des jeunes physicien.ne.s de la SFP), [Lien].

Presentations

Talks

  • APS Global Physics Summit, 18/03/2025. Quantum closures for neutrino moment transport.
  • SoCalDM #3 Workshop, UC Irvine, 28/02/2025. Fun with primordial neutrino asymmetries.
  • CERN Neutrino Platform Pheno Week, CERN, 17/02/2025. (No) constraints on primordial neutrino asymmetries.
  • GReCO seminar, IAP (Paris), 06/01/2025. Angular moments for neutrino transport: the quantum case.
  • HEP Seminar, UC San Diego, 10/12/2024. Closures for Quantum Neutrino Moment Transport.
  • COSMO'24 conference, Kyoto, 28/10/2024. Constraints on primordial lepton asymmetries with quantum neutrino transport.
  • Astrophysics and Cosmology Seminar, UC San Diego, 14/10/2024. Neutrino flavor transformation in dense environments: two case studies.
  • Neutrino Frontiers Workshop, 02/07/2024. Neutrino flavor transformation in dense environments.
  • N3AS Meeting, 02/06/2024. Neutrino flavor instabilities in neutron star mergers.
  • APS April Meeting, 05/04/2024. Neutrino fast flavor oscillations with moments: linear stability analysis and application to neutron star mergers.
  • Rising Researchers Seminar, 05/03/2024. New approaches to collective neutrino oscillations.
  • TAUP 2023, 28/08/2023. Moment neutrino evolution equations: application to fast-flavor instability in neutron star mergers.
  • INT Workshop, 25/07/2023. Moment neutrino evolution equations: application to fast-flavor instability in neutron star mergers.
  • Nuclear and Neutrino Astrophysics group (NC State University), 17/04/2023. Evolution of primordial neutrino asymmetries.
  • CNP seminar, Virginia Tech, 12/04/2023. Various approximations around the Quantum Kinetic Equations.
  • N3AS Meeting, 18/03/2023. Various approximations around the Quantum Kinetic Equations.
  • Nuclear and Neutrino Astrophysics group (NCSU), 17/10/2022. A precision calculation of neutrino decoupling.
  • IPhT seminar, 19/05/2022. Primordial neutrino asymmetry evolution in the early Universe.
  • NBIA seminar, 04/04/2022. Video Primordial neutrino asymmetry evolution in the early Universe.
  • Visit to TTK at Aachen, 02/2022. (i) Neutrino decoupling ; (ii) Evolution of primordial asymmetries.
  • LAPTh seminar, 03/02/2022. Primordial neutrino asymmetry evolution in the early Universe.
  • Café-club GECO, 08/12/2021. A precision calculation of neutrino decoupling.
  • Sydney-CPPC seminar, 28/10/2021. Video Primordial neutrino asymmetry evolution in the early Universe.
  • TAUP 2021, 31/08/2021. Video Precision calculation of neutrino evolution in the early Universe.
  • Workshop: Latest Advances in the Physics of BBN and Neutrino Decoupling, 13/04/2021. Flavour mixing effects on neutrino decoupling and BBN.
  • ICAP meeting, 17/12/2020. The effect of incomplete neutrino decoupling on Big Bang nucleosynthesis.
  • APC theory seminar, 08/12/2020. A precision calculation of neutrino decoupling (Link).
  • GDR Neutrino meeting, 24/11/2020, WG 3: Neutrinos in the Universe. A precision calculation of neutrino decoupling.
  • LUTH seminar, 05/11/2020. A precision calculation of neutrino decoupling (Link).
  • GReCO seminar, IAP (Paris), 19/10/2020. A precision calculation of neutrino decoupling (Link).

Posters

  • N3AS Meeting 2024, 06/2024. Neutrino flavor instabilities in a neutron star merger.
  • N3AS Meeting 2023, 03/2023. Approximation methods for neutrino evolution: from the early Universe to compact objects.
  • ISAPP 2021 summer school “Neutrino Physics, Astrophysics and Cosmology”, 21-30/07/2021. Precision calculation of neutrino evolution in the early Universe.
  • WIN 2021, 06/2021. Precision calculation of neutrino evolution in the early Universe.

Other academic service

Referee for the Journal of Cosmology and Astroparticle Physics (JCAP), Physics Letters B, Physical Review D and Physical Review Letters.

Endorser of Snowmass 2021 Letter of Intent - Cosmological neutrinos.

Endorser of Neutrino Theory in the Precision Era, input to the European Strategy for Particle Physics 2025 Update [2504.00014].