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Tsung-Dao Lee Institute Reveals Chiral Oscillation and Its Connection with Parity Violation

December 07, 2020      Author: Ge Shaofeng

It has been clearly verified by a large number of experiments that neutrino oscillation is the first new physical phenomenon beyond the Standard Model of particle physics. In the Standard Model, neutrinos are left-chiral, without a reformable mass term, but the existence of neutrino oscillations indicates that neutrinos have mass, and the masses of three neutrinos are not degenerate.

Neutrino oscillation usually refers to the oscillation that occurs between three taste eigenstates of neutrino, but it is not the only possible oscillation mode. Associate Professor Ge Shaofeng and post-doctor Pedro Pasquini from Tsung-Dao Lee Institute, SJTU have investigated a new oscillation mode—Chiral Oscillation—in a recent paper (Physics Letters B 811 (2020) 135961 [arXiv: 2009.01684 [hep-ph]] ). This new neutrino oscillation mode is proved possible based on the Parity Violation Theory proposed by Professor Tsung-Dao Lee and Professor Chen Ning Yang in 1956.

Parity Violation has established the reputation for Tsung-Dao Lee, the honorary director of Tsung-Dao Lee Institute, SJTU. Chiral Oscillation is a further inheritance and development of this theory, which expands theories and phenomena in neutrino oscillation. Therefore, it is of great significance to conduct this research at the institute.


The conventional derivation of neutrino oscillation treats neutrino mass eigenstate as plane wave with an overall evolution phase. Nevertheless, due to the intrinsic parity-violating nature of weak interactions, only the left-chiral neutrino can be produced as initial condition. On the other hand, the neutrino mass term connects the left-chiral component to the right-chiral one and unavoidably leads to generation of the later through oscillation. This chiral oscillation has significant consequences on the detection of the cosmological relic neutrinos. The event rate is reduced by a factor of 2 than the conventional prediction.

Affiliation: Tsung-Dao Lee Institute, SJTU

Translated by Fu Jing