Transversity distribution does not contribute to hard exclusive electroproduction of mesons

We show that in hard exclusive electroproduction, (Formula presented) the leading-twist hard-scattering coefficient for the production of a transversely polarized vector meson (Formula presented) vanishes to all orders of perturbation theory. This implies that this process cannot be used to measure the skewed transversity distribution of quarks in a hadron. In contrast, a recent calculation obtained a non-zero value at NLO. We show that this calculation is incorrect because it failed to include the necessary collinear subtractions. Our method of proof also applies to other processes whose hard-scattering coefficients are constrained by chirality and helicity conservation, and thus validates helicity selection rules based on these symmetries.