Fourth sound of holographic superfluids

We compute fourth sound for superfluids dual to a charged scalar and a gauge field in an AdS4 background. For holographic superfluids with condensates that have a large scaling dimension (greater than approximately two), we find that fourth sound approaches first sound at low temperatures. For condensates that a have a small scaling dimension it exhibits non-conformal behavior at low temperatures which may be tied to the nonconformal behavior of the order parameter of the superfluid. We show that by introducing an appropriate scalar potential, conformal invariance can be enforced at low temperatures. May 8, 2009 ∗e-mail: [email protected]