We show that fixed-$j$ holographic double deeply virtual Compton scattering (DDVCS) and its DVCS limit give a fixed-scale structural match to the singlet conformal-operator product expansion Wilson-kernel family of QCD in the leading-twist unpolarized singlet vector channel. The open-string $C_1(\delta ,\vartheta )$ hypergeometric kernel was derived by Nishio-Watari; the new closed-string result is that the Brower-Polchinski-Strassler-Tan (BPST) upper Witten vertex gives the same family with a different near-boundary power count, because ${\mathrm{\Delta }}_c(j)$ is fixed by the BPST trajectory rather than by open-Regge data. The Mellin exponent is therefore derived as ${\delta }_c(j)=j+{\mathrm{\Delta }}_c(j)-2=2j+{\gamma }_c(j)$ rather than inserted by hand. The even open branch gives the parallel unprotected counterpart in the projected singlet vector amplitude. At $Q=\mu ={\mu }_0={\mu }_{*}$, the point is not merely that equal-endpoint evolution is trivial; it is that the ultraviolet Witten vertex has already produced the fixed-$j$ conformal kernel before the lower conformal moment is matched. In the conformal partial-wave/conformal subtraction representation, beta-proportional conformal-anomaly terms and scheme transformations are coefficient/evolution bookkeeping away from the matching point, not replacements for the projected fixed-scale hypergeometric $\eta /\xi$ Wilson-kernel family. The protected/unprotected $j=2$ split identifies the protected closed branch with the ($-$) conformal partial wave and the even open branch with the unprotected ($+$) counterpart; these are mixed singlet eigenchannels, not literal unmixed quark/gluon operators at finite $N_c$. The comparison therefore gives a direct conformal-basis interpretation of the fixed-$j$ holographic $t$-channel Witten diagram: the ultraviolet vertex generates the universal Wilson-kernel family, while the lower vertex supplies the channel-dependent nonperturbative conformal moment.

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• Gauge-gravity dualities
• Quantum chromodynamics
• Field & string theory models & techniques