On a lightlike limit of entanglement

Understand

We study certain classes of $g_{++}$ deformations of theories arising in gauge/string realizations of nonrelativistic holography, some of which pertain to $z=2$ Lifshitz theories while others (pertaining to hyperscaling violation) comprise certain classes of excited states.

• Building on previous work, we consider holographic entanglement entropy for spacelike strip subsystems in a highly boosted (lightlike) limit, where the strip is stretched along the null $x^+$-plane.
• The leading divergence in entanglement in this null limit for these excited states is milder than the usual area law for spacelike subsystems in ground states.
• For ground states, the entanglement vanishes, perhaps consistent with ultralocality.