1. D.T. Son, Low-energy quantum effective action for relativistic superfluids, hep-ph/0204199 [ INSPIRE ].
2. M. Greiter, F. Wilczek and E. Witten, Hydrodynamic Relations in Superconductivity, Mod. Phys. Lett. B 3 (1989) 903 [ INSPIRE ].
3. S. Dubovsky, T. Gregoire, A. Nicolis and R. Rattazzi, Null energy condition and superluminal propagation, JHEP 03 (2006) 025 [ hep-th/0512260 ] [ INSPIRE ].
4. A. Nicolis, R. Penco and R.A. Rosen, Relativistic Fluids, Superfluids, Solids and Supersolids from a Coset Construction, Phys. Rev. D 89 (2014) 045002 [ arXiv:1307.0517 ] [ INSPIRE ].
5. A. Nicolis, R. Rattazzi and E. Trincherini, The Galileon as a local modification of gravity, Phys. Rev. D 79 (2009) 064036 [ arXiv:0811.2197 ] [ INSPIRE ].