In the region of hard photon energies, radiative leptonic decays represent important probes of the internal structure of hadrons.
Moreover, radiative decays can provide independent determinations of Cabibbo-Kobayashi-Maskawa matrix elements with respect to purely leptonic or semileptonic channels.
Prospects for a precise determination of leptonic decay rates with emission of a hard photon are particularly interesting, especially for the decays of heavy mesons for which currently only model-dependent predictions, based on QCD factorization and sum rules, are available to compare with existing experimental data.
We present a non-perturbative lattice calculation of the structure-dependent form factors which contribute to the amplitudes for the radiative decays $H \to \ell \nu_\ell \gamma$, where $H$ is a charged pseudoscalar meson, using the Domain Wall formulation of lattice fermions.
With moderate statistics, thanks to the use of a sine-cardinal-reconstruction technique and improved estimators, we are able to provide rather precise, first-principles results for the form factors in the full kinematical (photon-energy) range for both light and heavy mesons.