Inverse neutrinoless doubleβdecay reexamined

We critically reexamine the prospects for the observation of the $\Delta L=2\mathrm{}$ lepton-number-violating process $e^{-}{e}^{-}\to W^{-}{W}^{-}$ using the $e^{-}{e}^{-}$ option of a high-energy $e^{+}{e}^{-}$ collider (NLC). We find that, except in the most contrived scenarios, constraints from neutrinoless double $\beta$ decay render the process unobservable at an NLC of $\sqrt{s}<2\mathrm{}$ TeV. Other $\Delta L=2\mathrm{}$ processes such as $\gamma \gamma \to {\ell }^{+}{\ell }^{+}{W}^{-}{W}^{-}$, $e^{-}\gamma \to {\nu }_e{\ell }^{-}{\ell }^{-}{W}^{+}$, $e^{-}{e}^{-}\to {\nu }_e{\nu }_e{\ell }^{-}{\ell }^{-}(\ell =\mu , \tau )$, and $e^{-}\gamma \to e^{+}{W}^{-}{W}^{-}$, which use various options of the NLC, require a $\sqrt{s}$ of at least 4 TeV for observability.