Tomas Andrade

A simple holographic model of momentum relaxation

A bstractWe consider a holographic model consisting of Einstein-Maxwell theory in d + 1 bulk spacetime dimensions with d − 1 massless scalar fields. Momentum relaxation is realised simply through spatially dependent sources for operators dual to the neutral scalars, which can be engineered so that the bulk stress tensor and resulting black brane geometry are homogeneous and isotropic. We analytically calculate the DC conductivity, which is finite. In the d = 3 case, both the black hole geometry and shear-mode currentcurrent correlators are those of a sector of massive gravity.

AdS/CFT beyond the unitarity bound

A bstractScalars in AdSd+1 with squared masses in the Breitenlohner-Freedman window

Boundary conditions for scalars in Lifshitz

- {d^{{2}}}/{4} \leqslant {m^{{2}}} < - {d^{{2}}}/{4} + {1}

Holographic isotropisation in Gauss-Bonnet gravity

(in units with the AdS scale ℓ set to 1) are known to enjoy a variety of boundary conditions. For larger masses

Boundary conditions for metric fluctuations in Lifshitz

{m^{{2}}} > - {d^{{2}}}/{4} + {1}

Beyond the unitarity bound in AdS/CFT(A)dS

, unitarity bounds in possible dual CFTs suggest that such general boundary conditions should lead to ghosts. We show that this is not always the case as, for conformally-invariant boundary conditions in Poincaré AdS that would naively violate unitarity bounds, the system is generically ghost-free. Conflicts with unitarity bounds are avoided due to the presence of unexpected pure gauge modes and an associated infrared divergence. The expected ghosts appear when the IR divergence is removed either by deforming these boundary conditions or considering global AdS.