Solution to the B -> pi K Puzzle in a Flavor-Changing Z' Model
  Recent experiments suggest that certain B -> pi K branching ratios are inconsistent with the standard model expectations. We show that a flavor-changing Z' provides a solution to the problem. Electroweak penguin amplitudes are enhanced by the Z' boson for select parameters. We discuss implications for the Z' mass and its couplings to the standard model fermions. We also show that the solution is consistent with constraints from the CP asymmetries of the B -> phi K_S decay. 
Vernon Barger, Cheng-Wei Chiang, Paul Langacker, and Hye-Sung Lee