Professor Yongzhong Qian

This group's research interests include: beyond-standard-model physics and their effects in astrophysical environments; supernova explosion and nucleosynthesis; transport properties of neutron star matter; and chemical evolution of galaxies. These topics are at the intersection among nuclear/particle physics, astrophysics, and cosmology, and studying them requires substantial computing resources.

The group is working on three main projects:

• Effects of beyond-standard-model physics on stellar evolution and supernova explosion: Due to their weak interaction, neutrinos are the predominant energy sink in late stages of evolution of a massive star. They also carry away the gravitational binding energy of the neutron star formed in a supernova and play important roles in the explosion mechanism. The astronomical evidence for dark matter strongly suggests beyond-standard-model physics, which would imply new particles with interactions even weaker than neutrinos. To study the effects of such beyond-standard-model particles, the researchers will include their production in stellar interior during the evolution and explosion of a massive star. This covers the entire life of the star from birth to death.
• Supernova necleosynthesis: The last decade has brought significant progress in supernova physics and self-consistent, 3D simulations are now available. Such simulations cannot afford to include a full nuclear reaction network that is necessary to give accurate predictions of the istopes produced by the supernova explosion and these calculations need to be done in a post-processing step. The researchers of this group prepare simulation data and process it with a nuclear reaction network to investigate the effect of multi-dimensional dynamics on the production of the elements and implications for chemical evolution and observations.
• Collective neutrino flavor oscillations: Theoretically and experimentally it is now well established that neutrinos undergo flavor transformations and these are affected by interactions with the medium in which the particles propagate. In a supernova environment, the medium contains a large fraction of neutrinos, such that neutrino-neutrino interactions lead to non-linear effects for the neutrino flavor evolution. To fully address this effect is necessary to solve a very large many-body quantum system. The researchers address the full solution of this problem and compare to commonly applied approximations. This type of neutrino oscillation also has implications for neutrino observations and nucleosynthesis, which are also addressed by the researchers.