Entanglement, Soft Modes, and Celestial CFT

Understand

We revisit the calculation of vacuum entanglement entropy in free Maxwell theory in four-dimensional Minkowski spacetime.

• Weyl invariance allows for this theory to be embedded as a patch inside the Einstein static universe.
• We use conformal inversions to extend the conformal primary solutions of the equations of motion labelled by a boost-weight $\Delta = 1 + i\lambda$ to an inverted Minkowski patch centered at spacelike infinity of the original patch.
• For $\lambda \neq 0$ these solutions admit an expansion in terms of wavefunctions supported in the (future) Milne wedges of the original and inverted Minkowski patches, that diagonalize the respective Milne times.