High-order harmonic emission is investigated by numerical solution of the weakly relativistic, two-dimensional Schr?dinger equation for the case of ultra-intense laser-driven tightly bound systems (for example, multiply charged ions such as O7+ exposed to laser fields of the order of 1018?W?cm-2 at 248?nm). In contrast to their usual substantial decrease, the low-order harmonics having an energy less than the ionization potential exhibit a high-efficiency (i.e.?intense) plateau with a well defined cutoff. The shape of this plateau is found to depend on the shape of the binding potential. A classical `surfing' mechanism for the generation of these harmonics is proposed that does not involve tunnelling and that nevertheless explains the observed cutoff. Thus we call them `nontunnelling harmonics'. The significance of relativistic effects for these harmonics is investigated and found to be small, despite the high laser intensity, because of the absence of tunnelling.

In models with Abelian flavor symmetry the small mixing angles and mass ratios of quarks and leptons are typically given by powers of small parameters characterizing the spontaneous breaking of flavor symmetry by ``flavon'' fields. If the scale of the breaking of flavor symmetry is near the weak scale, flavon exchange can lead to interesting flavor-violating and $\mathrm{CP}$ violating effects. These are studied. It is found that ${d}_{e},$ $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e+\ensuremath{\gamma},$ and $\ensuremath{\mu}\ensuremath{-}e$ conversion on nuclei can be near present limits. For a significant range of parameters $\ensuremath{\mu}\ensuremath{-}e$ conversion can be the most sensitive way to look for such effects.