Zhi-zhong Xing, Ye-Ling Zhou (2014) ‘Geometry of the effective Majorana neutrino mass in the neutrinoless double-beta decay‘, Arxiv .


“The neutrinoless double-beta (0νββ) decay is a unique process to identify the Majorana nature of massive neutrinos, and its rate depends on the size of the effective Majorana neutrino mass ⟨m⟩ee. We put forward a novel “coupling-rod” diagram to describe ⟨m⟩ee in the complex plane, by which the effects of the neutrino mass ordering and CP-violating phases on ⟨m⟩ee are intuitively understood. We show that this geometric language allows us to easily obtain the maximum and minimum of |⟨m⟩ee|. It remains usable even if there is a kind of new physics contributing to ⟨m⟩ee, and it can also be extended to describe the effective Majorana masses ⟨m⟩eμ, ⟨m⟩eτ, ⟨m⟩μμ, ⟨m⟩μτ and ⟨m⟩ττ which may appear in some other lepton-number-violating processes”.