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In this note, I revisit the problem of computing the entanglement entropy ofa single interval in the ground state of a 2d CFT. I write the leading-orderresult in three different ways: once by doing the replica trick with the$n$-replicated cylinder partition function computed in the ``closed stringchannel"; once by computing the $n$-replicated cylinder partition function inthe ``open string channel", where the entanglement entropy can be related tothe density of states in a boundary CFT defined on the interval; and forholographic CFTs, once as the log of a Plancherel measure for a certainnoncompact quantum group. I comment on the implications for what theRyu-Takayanagi area term might be counting in holographic CFTs.

A new look at the entanglement entropy of a single interval in a 2d CFT