You can read what the Princeton University public finance expert says at this link. Here is the bottom line:
I analyze the Romney proposal taking into account the additional income that might be generated by economic growth. The main conclusion is that under plausible assumptions, a proposal along the lines suggested by Governor Romney can both be revenue neutral and keep the net tax burden on high-income individuals about the same. That is, an increase in the tax burden on lower and middle income individuals is not required in order to make the overall plan revenue neutral.