RUI: Quantum Kinetics of Neutrinos: Leveraging the Universe at the Interface of Neutrino and Nuclear Astrophysics

Neutrinos are the ghostly, shape-shifting enigmas of the Standard Model of particle physics. Trillions of neutrinos from the Sun pass through our bodies every second of the day. They don’t affect us, and most of them changed their identity -- their “flavor” -- while streaming from the core of the Sun.

These interesting properties owe to their fundamental quantum mechanical nature; although all particles in the universe evolve quantum mechanically, the quantum effects are especially acute in the evolution of neutrinos. For decades, terrestrial experiments unveiled the properties of neutrinos. However, their ghost-like nature presents a significant barrier to fully elucidate the neutrino properties.

By contrast, moments after the Big Bang the universe consisted of a primordial soup of fundamental particles so hot and dense that ghostly neutrinos nevertheless played an important role in the dynamics of the universe. This provides an opportunity to use the early universe as a complementary probe to explore neutrino physics. This project leverages upcoming cosmological observations and terrestrial neutrino experiments by performing high-fidelity simulations of neutrino evolution in the early universe.

These investigations form an intriguing backdrop for the PI to train undergraduate student researchers, building skills that are valuable across a range of 21st century careers.

Upcoming high-precision cosmological observations and neutrino laboratory experiments provide an opportune environment to explore questions in fundamental neutrino physics. Leveraging these advances requires high fidelity theoretical calculations to connect observation, experiment, and theory. This project explores the quantum kinetic evolution of neutrinos through the hot and dense plasma of the early universe.

This evolution is affected by coherent, unitary quantum mechanical behavior as well as decoherent inelastic scattering. In the early universe, large fluxes of neutrinos nonlinearly affect both the coherent quantum evolution and decoherent scattering through neutrino-neutrino interactions. Connecting cosmological observations to fundamental neutrino physics requires a self-consistent examination of the nonlinear quantum kinetic neutrino evolution because this evolution plays an important role in the dynamics of the expanding universe as well as the interconversion between protons and neutrons.

The goal of this project is to solve the quantum kinetic equations for neutrinos in many theoretical scenarios in the early universe. In doing so, we look to build a broader understanding of this nonlinear evolution, to explore the astrophysical feedback and consequences of this evolution, and to aim toward leveraging the universe as a laboratory to study fundamental physics.

This project advances the objectives of "Windows on the Universe: the Era of Multi-Messenger Astrophysics", one of the 10 Big Ideas for Future NSF Investments.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.