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The fundamental process of neutrinoless double beta decay, nn ppe^-e^-, dominated by the exchange of light Majorana neutrinos, is studied in the framework of chiral effective field theory. Considering neutrinos as virtual states, we evaluate the contributions of finite nucleon size to the transition amplitude in a non-perturbative manner, as opposed to expanding these effects in powers of momentum. Based on the nucleon form factors expressed in terms of the dipole and Kelly parametrizations, we find that, at the leading order, the present scheme could renormalize the amplitude in the context of the standard mechanism and provide predictions consistent with the previous investigations. Consequently, we argue that the impact of the effects of finite nucleon size on the amplitude is comparable to that of the leading-order contact term introduced in Phys. Rev. Lett. 120, 202001 (2018) in a perturbative scheme. Our results provide not only a benchmark calculation for the transition amplitude between two schemes but also evidence for the reasonableness of non-perturbative treatment for the effects of finite nucleon size in conventional nuclear many-body methods.
Liu et al. (Thu,) studied this question.