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Applying the method of light-cone sum rules with photon distributionamplitudes, we compute the subleading-power correction to the radiativeleptonic $B \to \gamma \ell \nu$ decay, at next-to-leading order in QCD for thetwist-two contribution and at leading order in $\alpha_s$ for the higher-twistcontributions, induced by the hadronic component of the collinear photon. Theleading-twist hadronic photon effect turns out to preserve the symmetryrelation between the two $B \to \gamma$ form factors due to the helicityconservation, however, the higher-twist hadronic photon corrections can yieldsymmetry-breaking effect already at tree level in QCD. Using the conformalexpansion of photon distribution amplitudes with the non-perturbativeparameters estimated from QCD sum rules, the twist-two hadronic photoncontribution can give rise to approximately 30\% correction to theleading-power "direct photon" effect computed from the perturbative QCDfactorization approach. In contrast, the subleading-power corrections from thehigher-twist two-particle and three-particle photon distribution amplitudes areestimated to be of ${\cal O} (3 \sim 5\%)$ with the light-cone sum ruleapproach. We further predict the partial branching fractions of $B \to \gamma\ell \nu $ with a photon-energy cut $E_{\gamma} \geq E_{\rm cut}$, which are ofinterest for determining the inverse moment of the leading-twist $B$-mesondistribution amplitude thanks to the forthcoming high-luminosity Belle IIexperiment at KEK.

Subleading-power corrections to the radiative leptonic $B \to \gamma \ell \nu$ decay in QCD