******** CTCD/NTHU HEP Seminar ********

Speaker ：Mr. Heng-Hao Chen (AS IoP).

Title ：Fast and Slow Collective Neutrino Flavor Conversions in
Core-Collapse Supernovae.

Time ：12:30-13:30, Thursday, 2025/3/13

Place ：R521, 5F, General Building II, Nat'l Tsing Hua Univ.

Host ： Prof. Po-Yen Tseng (NTHU)

Abstract:
Neutrino flavor conversions are crucial for shaping the dynamics of
core-collapse supernovae and other astrophysical environments dense in
neutrinos. In this talk, I will present insights from two complementary
investigations that focus on the two scenarios of collective neutrino
flavor oscillations—fast conversions and slow conversions. The first
study explores fast flavor conversions, revealing that nearly complete
flavor depolarization in a certain neutrino phase space is reached when
averaged over a length scale much longer than the oscillation length,
dictated by net neutrino e−x lepton number conservation. In the second
study, we turn to slow flavor conversions and demonstrate that a dense
neutrino gas rapidly evolves toward a state of approximate flavor
equipartition, again subject to overall lepton number conservation.
Notably, this equilibrium emerges within just a few factors of the
inverse vacuum oscillation timescale, implying that flavor
transformations can operate efficiently across large spatial regions.
These results highlight the importance of integrating both fast and slow
flavor mechanisms into astrophysical simulations to more accurately
probe supernova dynamics.