The entanglement and relative entropy of a chiral fermion on the torus. (arXiv:1906.02207v2 [hep-th] UPDATED)

We derive the entanglement entropy of chiral fermions on the circle at
arbitrary temperature. The spin-sector contribution depends only on the total
length of the entangling region, regardless of the configuration of the
intervals. Thus three-partite information provides a global indicator for the
spin boundary conditions. Together with the modular Hamiltonian, our results
provide a systematic way of obtaining relative entropy on the torus.

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