134 Chapter 5: pQCD vs. AdS/CFT Figure 5.5: R c $_{AA}$( p$_{T}$ ) and R b $_{AA}$( p$_{T}$ ) for $_{Rhic}$using AdS/CFT drag and the pQCD- based WHDG model. Note how the rapid increase in n$_{Q}$ for Rhic as seen in Fig. 5.4 overcomes the decrease in the fractional energy loss for the pQCD predictions for charm and bottom R$_{AA}$ ( p$_{T}$ ) so that both AdS/CFT drag and pQCD results decrease as a function of momentum at $_{Rhic}$. be masked by taking extreme energy loss extrapolations to $_{Lhc}$. However the double ratio R cb revealed very generic behavior, insensitive to the input parameters and radically different for the two coupling limits. Of crucial im- portance is the momentum range over which pQCD and AdS/CFT drag are self-consistent. Certainly pQCD must apply for p$_{T}$ → ∞ , but the scale below which nonperturbative effects become important is not yet well understood. Supposing that the AdS/CFT correspondence is relevant for heavy ion col- lisions, drag calculation momentum validity is limited from above. Since γ$_{c}$ depends on M$_{Q}$ but the hard pQCD scale does not there is likely a large re-