| Abstract: | The neutrinoless double-beta (0νββ) decay is a unique process used 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. |
