Breakdown of the initial value formulation of scalar-tensor gravity and   its physical meaning
  We revisit singularities of two distinct kinds in the Cauchy problem of general scalar-tensor theories of gravity (previously discussed in the literature), and of metric and Palatini f(R) gravity, in both their Jordan and Einstein frame representations. Examples and toy models are used to shed light onto the problem and it is shown that, contrary to common lore, the two conformal frames are equivalent with respect to the initial value problem. 
Valerio Faraoni and Nicolas Lanahan-Tremblay (Bishop's University)