doi:10.1007/JHEP02(2026)020engAsorey, ManuelKrein, GastãoPardina, MiguelShapiro, Ilya L.Reflection positivity in a higher-derivative model with physical bound states of ghostsART-2026-148134The inclusion of higher derivatives is a necessary condition for a renormalizable or superrenormalizable local theory of quantum gravity. On the other hand, higher derivatives lead to classical instabilities and a loss of unitarity at the quantum level. A standard way to detect such issues is by examining the reflection positivity condition and the existence of a Källén-Lehmann spectral representation for the two-point function. We demonstrate that these requirements for a consistent quantum theory are satisfied in a theory we have recently proposed. This theory is based on a six-derivative scalar field action featuring a pair of complex-mass ghost fields that form a bound state. Our results support the interpretation that physical observables can emerge from ghost dynamics in a consistent and unitary framework.2026http://zaguan.unizar.es/record/16875810.1007/JHEP02(2026)020http://zaguan.unizar.es/record/168758oai:zaguan.unizar.es:168758info:eu-repo/grantAgreement/ES/DGA-FSE/E21-17Rinfo:eu-repo/grantAgreement/ES/MICINN/PGC2022-126078NB-C21Journal of High Energy Physics 2026, 20 (2026), [14 pp.]byhttps://creativecommons.org/licenses/by/4.0/deed.esinfo:eu-repo/semantics/openAccess