Gapless and gapped holographic phonons

Understand

We study a holographic model where translations are both spontaneously and explicitly broken, leading to the presence of (pseudo)-phonons in the spectrum.

• The weak explicit breaking is due to two independent mechanisms: a small source for the condensate itself and additional linearly space-dependent marginal operators.
• The low energy dynamics of the model is described by Wigner crystal hydrodynamics.
• In absence of a source for the condensate, the phonons remain gapless, but momentum is relaxed.