  It was shown in PHYSICAL REVIEW B 92, 085409 (2015) that the dynamics of a
pair of electrons in graphene can be mapped onto that of a single particle with
negative effective mass, leading to bound states of positive energy despite the
formally repulsive interaction. However, this conclusion was based on the
analysis of the two--particle problem, neglecting the role of the Dirac sea and
the many--body effects. The two dominant such effects at zero temperature are
screening of the Coulomb interaction by the Dirac sea, and reduction of the
available phase space due to Pauli blocking of transitions into the states
below the Fermi level. We show that these effects result in strong
renormalization of the binding energy, but do not destroy the metastable
states. Thus the binding energies are strongly dependent on the chemical
potential owing to the combined effects of screening and Pauli blocking. Hence,
the quasibound resonances can be tuned by electrostatic doping.
