Twisted type IIB supergravity as BCOV theory

Let $X$ be a Calabi–Yau $5$-fold, with type IIB supergravity placed in the Calabi–Yau background and its bosonic ghost field set to the covariantly constant Killing spinor $(Q,0)$. Type IIB twist conjecture. This twist is equivalent to BCOV theory on $X$. This identifies the twisted type IIB supergravity theory with a holomorphic closed-string field theory; the source notes that the minimal version of BCOV theory is expected, while a full equivalence is not proved.