  We present a theoretical and numerical investigation of the effect of a
time-varying external driving force on interface growth. First, we derive a
relation between the roughening exponents which comes from a generalized
Galilean invariance, showing how the critical dimension of the model is tunable
with the external field. We further conjecture results for the exponents in two
dimensions, and find consistency with data obtained through simulations of two
models we expect to be in the same universality class. Finally, we discuss how
our results can be investigated experimentally.
