DSR as an explanation of cosmological structure

Deformed special relativity (DSR) is one of the possible realizations of a varying speed of light (VSL). It deforms the usual quadratic dispersion relations so that the speed of light becomes energy dependent, with preferred frames avoided by postulating a nonlinear representation of the Lorentz group. The theory may be used to induce a varying speed of sound capable of generating ( near) scale-invariant density fluctuations, as discussed in a recent letter. We identify the nonlinear representation of the Lorentz group that leads to scale invariance, finding a universal result. We also examine the higher order field theory that could be set up to represent it.