## 17 Conclusions  
It may be concluded that the relation between the momentum and the wavelength of the droplet model is quantitatively in good agreement with [PERSON]'s relation in QM. The quantification of the droplet model was based on the assumption that the three equilibria of the charged droplet would correspond to the electron, muon and tau (i.e., the three charged leptons of the standard model). Since the quantification of the droplet model seems to be correct (in view of the fact that Em.QM is then able to reproduce the value of [PERSON]'s constant), it is plausible that the three charged leptons indeed correspond to the equilibria of a droplet of charge. This answers the first question \"why do three charged leptons exist?\"  
In reverse, starting from the given value of [PERSON]'s constant, the analysis by Em.QM gives one relation between the two mass ratios \(m_{muon}/m_{electron}\) and \(m_{tau}/m_{electron}\), Equation (34). If a second relation could be found, it would fix these ratios. A second relation has not been found (yet), although it is plausible that such a relation must exist because one expects that the mass ratios of the various guises of the electron are determined by the laws of nature and are not completely arbitrary. The second question, \"what determines the mass ratios?\", cannot yet be answered, although a first indication in which direction to look for an answer has been found.  
This research received no external funding.  
The authors declare no conflict of interest.  
Symbols recurring throughout the text are here listed. Non-recurring symbols are explained immediately underneath the expressions in which they are used.  
\begin{tabular}{l l} \(a\) & width of potential well (see Figure 2), radius of [PERSON]'s electron model \\ \(A,B,C\) & constants in surface-tension-like force, Equation (21) \\ \(c\) & velocity of light \\ \(E\) & field strength, energy \\ \(h\) & [PERSON]'s constant \\ \(k\) & constant factor defined in Equation (28) \\ \(K\) & constant in \"De Broglie-like\" relation of Em.QM, defined in Equation (34), \(K\cong h\) \\ \(m\) & effective mass \(\left.\frac{1}{2}m_{em}(s)\right|_{s=s_{e}}\) of droplet at static equilibrium (common electron) \\ \(m_{bare}\) & material mass \\ \(m_{cm}\) & electromagnetic mass, defined in Equation (5) \\ \(m_{em}{}^{*}\) & generalised electromagnetic mass \\ \(p\) & momentum \\ \(q\) & total charge of droplet, in Equation (34) equal to unit charge \\ \end{tabular}  
\begin{tabular}{l l} \(Q_{s}\) & generalised expansion force \\ \(s(t)\) & length of droplet, see Figure 2 \\ \(s_{equ}\) & static equilibrium length without external influences \\ \(U_{es}\) & electrostatic energy of droplet, defined in Equation (3) \\ \(U_{es}\)\({}^{*}\) & electrostatic energy of droplet with charge distribution \(\sigma\) modified into \(\sigma.(z-z_{m})/s\) \\ \(v_{m}\) & velocity of midpoint, as defined in Figure 2 \\ \(v_{av}\) & average translation velocity \\ \(\Delta v\) & amplitude of periodic velocity perturbation \\ \(\alpha\) & non-dimensional constant depending on distribution of charge within the droplet \\ \(\gamma\) & short for \(\frac{2}{3}\ \frac{q^{2}}{4\pi\epsilon_{0}}\ \frac{1}{c^{3}}\) \\ \(\epsilon_{0}\) & vacuum permittivity \\ \(\lambda_{beat}\) & wavelength of beats (Section 16) \\ \(\mu\) & mass ratio muon/common electron \\ \(\sigma\) & charge density \\ \(\tau\) & mass ratio tau particle/common electron \\ \(\Phi\) & potential field \\ \(\omega_{0}\) & \"zero-speed frequency\", defined in Equation (27) \\ Indices: \\ _av_ & time averaged \\ \(e\) & pertaining to electron \\ _equ_ & pertaining to static equilibrium without external forces \\ \(\mu\) & muon \\ \(\tau\) & tau particle \\ Superscripts: \\ \(*\) & pertaining to modified charge distribution \(\sigma.\ \left(\frac{z-z_{m}}{s}\right)\) \\ \end{tabular}