Modification to Special Relativity
  The speed of light is usually taken as one of the fundamental constants. String, and field, theories appear to require the altercation of this constant into a functional form $E(m,c)$ which is not $E=mc^2$. The analysis requires the re-interpretation of the renormalization group flow equations. There are quantum corrections to the mass-energy relation generically for particles of any sort. A breakdown of special relativity follows. Cosmological data might be one of the best testbeds to analyze the computable functional forms of the mass energy relations. 
Gordon Chalmers