Jeroen S.W. Lamb:

Resonant driving and k-symmetry

abstract:

A particular type of `resonant' periodic driving of a symmetric dynamical 
system may cause the time-one map of the driven system to have a nontrivial 
root that possesses less symmetry than the time-one map itself. The latter 
phenomenon is called $k$-symmetry. Some examples and consequences to the 
dynamical behaviour are pointed out briefly.