HET Journal club: Surbhi Khetrapal

Speaker: Surbhi Khetrapal

Title: Local quenches: universal corrections to entanglement entropy and quantum chaos.

Abstract: We study the time evolution of single interval Rényi and entanglement entropies following local quantum quenches in two dimensional conformal field theories at finite temperature for which the locally excited states have a finite temporal width. We show that, for local quenches produced by the action of a conformal primary field, the time dependence of Rényi and entanglement entropies at second order in width is universal. It is determined by the expectation value of the stress tensor in the replica geometry.
We also study local quenches in 2d CFTs at large-c by operators carrying higher spin charge. Viewing such states as solutions in Chern-Simons theory, representing infalling massive particles with spin-three charge in the BTZ background, we use the Wilson line prescription to compute the single-interval entanglement entropy and scrambling time following the quench. We find that the change in entanglement entropy is finite (and real) only if the spin-three charge q is bounded by the energy of the perturbation E, as |q|/c < E^2/c^2. We further find that the scrambling time for the two-sided mutual information between two intervals in the thermofield double state increases with increasing spin-three charge, diverging when the bound is saturated. For larger values of the charge, the scrambling time is shorter than for pure gravity and controlled by the spin-three Lyapunov exponent 4\pi/\beta.