Universal Bounds on Transport in Holographic Systems with Broken Translations

Understand

We study the presence of universal bounds on transport in homogeneous holographic models with broken translations.

• We verify numerically that, in holographic systems with momentum dissipation, the viscosity to entropy bound might be violated but the shear diffusion constant remains bounded by below.
• This confirms the idea that $\eta/s$ loses its privileged role in non-relativistic systems and that, in order to find more universal bounds, one should rather look at diffusion constants.
• We strengthen this idea by showing that, in presence of spontaneously broken translations, the Goldstone diffusion constant satisfies a universal lower bound in terms of the Planckian relaxation time and the butterfly velocity.