A New Theoretical Method to determine the Unknown Neutrino Mass-Hierarchy
-- Selected as A Highlight Topical Review of 2013 in Journal of Physics G --
Three flavors of active (electron-, mu- and tau-type) neutrinos are known to have finite masses and show the oscillation phenomena during their passage through space or matter inside the sun and supernovae (SNe). It is one of the ultimate purposes in modern physics and cosmology to determine their masses and oscillation properties to construct a unified theory of elementary particles and fields beyond the standard model because neutrino mass is the unique experimental evidence which indicates the breakdown of the standard model. There are still two unknown parameters, i.e. the mass hierarchy (normal or inverted) and the CP violation phase. Toshio Suzuki (Nihon University/NAOJ) and Toshitaka Kajino (NAOJ) have proposed an astronomical method to determine the mass hierarchy in terms of SN nucleosynthesis of specific elements that were produced by the energetic neutrinos interacting with abundant nuclei inside the SNe under the MSW effects of neutrino oscillation. They also prove theoretically that the proposed method is robust almost independent of the Hamiltonians assumed in the theoretical calculations of quantum neutrino-nucleus interaction cross-sections. This paper was selected as a highlight topical review of 2013 in Journal of Physics G.
In the figure it is shown that the inverted mass hierarchy is statistically more preferred from the comparison of the Li7/B11 abundance ratio between theoretical prediction and observation from presolar grains which originate from SNe ejecta.
T. Suzuki and T. Kajino, J. Phys. G40 (2013), 083101.