Beyond Calabrese-Cardy Scaling: Exceptional-Point Sensitivity and the de Sitter RT Surface

Abstract

Entanglement entropy at one-dimensional criticality typically follows the Calabrese--Cardy scaling. In the non-Hermitian critical free-fermion systems studied here, however, we find an additional interval-independent contribution $S_{\mathrm{res}}=\log (\Delta L)$, which allows the entropy to remain sensitive to energy gaps below the finite-size scale, $\Delta <1/L$. We refer to this term as the residual entropy. To understand its infrared origin, we examine finite-depth non-unitary continuous multiscale entanglement renormalization on a ring. Terminating the critical RG circuit before its singular final layer leaves a two-site infrared state. We calculate the entropy of this state directly from its correlation matrix and recover the same \(\log(ΔL)\) dependence. The emergent de Sitter geometry provides a complementary geometric interpretation: extremal curves associated with different boundary intervals extend to a common infrared endpoint, suggesting how the entanglement retained there can contribute equally to their entropies.

arXiv comment8 pages, 5 figures