be mediated by Majorana neutrino propagation, depending on the magnitude of the effective neutrino mass given by ${\langle m_{\nu}\rangle}=\sum_j U_{ej}^2 m_j$. This mechanism is hence forth referred to as the [*the mass mechanism*]{}. The mass mechanism has attracted most of the attention within the community. The reason for this “bias” is rather straightforward: Neutrinos exist and oscillation experiments [@Fukuda:1998mi; @Ahmad:2002jz; @Eguchi:2002dm; @Abe:2011sj; @Adamson:2011qu; @Abe:2011fz; @An:2012eh; @Ahn:2012nd] have shown that (at least two) neutrinos have non-zero masses. Thus, if neutrinos are indeed Majorana particles, the mass mechanism is guaranteed to give a contribution to the [$0\nu\beta\beta$ ]{}decay amplitude — in this sense the mass mechanism is the minimal possibility to generate [$0\nu\beta\beta$ ]{}decay. With the assumption of the mass mechanism being the dominant contribution, the current limits for the half-life of [$0\nu\beta\beta$ ]{}decay [@KlapdorKleingrothaus:2000sn; @Auger:2012ar] correspond to the limits ${\langle m_{\nu}\rangle}\lsim (0.2-0.35)$ eV \[${\langle m_{\nu}\rangle}\lsim
(0.17-0.30)$ eV\] for $^{76}$Ge \[$^{136}$Xe\] using the latest QRPA matrix elements of [@Faessler:2012ku] to ${\langle m_{\nu}\rangle}\lsim 0.53$ eV \[${\langle m_{\nu}\rangle}\lsim 0.34$ eV\] with the matrix elements calculated within the shell model [@Menendez:2008jp; @Menendez:2011zza]. Future limits of order $T^{0\nu\beta\beta}_{1/2} \sim 10^{27}$ yr will then probe ${\langle m_{\nu}\rangle}\lsim (0.02-0.06)$ eV that is of the order of the mass 