Reflected multi-entropy in AdS/BCFT and island phases

Construct reflected multi-entropy in AdS/BCFT and extend it to island phases by determining the canonical-purification replica construction, the associated EOW-brane-ending multiway cuts, defect or extremal-web conditions, and the required gravitational extremization.

Background

Reflected multi-entropy uses the multi-entropy replica contraction on a canonical purification, so its bulk dual is expected to involve multiway cuts of an entanglement wedge rather than the absolute bulk webs studied in the paper. In AdS/BCFT, these cuts may meet the EOW brane and can produce boundary-ending channels and additional factorization transitions.

The authors leave the construction and its extension to island phases unresolved, including the simultaneous treatment of canonical purification, defect or extremal-web conditions, and gravitational extremization.

References

We likewise defer to forthcoming work the reflected-multi-entropy construction in AdS/BCFT and its extension to island phases, where canonical purification, defect/extremal-web conditions and gravitational extremization must be treated simultaneously.

— Multipartite Entanglement Geometry in AdS/BCFT  (2610.11921 - Basu et al., 8 Oct 2026) in Section 6, “Summary and outlook”