  We study Renyi and von-Neumann entanglement entropy of excited states created
by local operators in large N (or large central charge) CFTs. First we point
that a naive large N expansion can break down for the von-Neumann entanglement
entropy, while it does not for the Renyi entanglement entropy. This happens
even for the excited states in free Yang-Mills theories. Next, we analyze
strongly coupled large N CFTs from both field theoretic and holographic
viewpoints. We find that the Renyi entanglement entropy of the excited state
produced by a local operator, grows logarithmically under its time evolution
and its coefficient is proportional to the conformal dimension of the local
operator.
