We discuss the tension between discrete flavour symmetries and extended
scalar sectors arising from lepton flavour violation experiments. The key point
is that extended scalar sectors will generically lead to flavour changing
neutral currents, which are strongly constrained by experiments. Due to the
large parameter space in the scalar sector such models will, however, usually
have no big problems with existing and future bounds (even though the models
might be constrained). This changes considerably once a flavour symmetry is
imposed in addition: Due to the symmetry, additional relations between the
different couplings arise and cancellations become impossible in certain cases.
The experimental bounds will then constrain the model severely and can easily
exclude it. We consider two examples which show how these considerations are
realized. The same logic should apply to a much wider class of models.Comment: 19 pages, 2 figures; Introduction extended, typos corrected, charged
lepton sector of model 2 corrected; matches journal versio
