Gauge Issues in Extended Gravity and f(R) Cosmology
  We consider issues related to the conformal mapping between the Einstein and
Jordan frames in f(R) cosmology. We consider the impact of the conformal
transformation on the gauge of a perturbed system and show that unless the
system is written in a restricted set of gauges the mapping could produce an
inconsistent result in the target frame. Newtonian gauge lies within the
restricted group but synchronous gauge does not. If this is not treated
carefully it could in principle contaminate numerical calculations.
