Long-range S-wave DD* interaction in covariant chiral effective field theory

Motivated by the recent lattice QCD study of the DD* interaction at unphysical quark masses, we perform a theoretical study of the DD* interaction in covariant chiral effective field theory. In particular, we calculate the relevant leading-order two-pion exchange contributions. The results compare favorably with the lattice QCD results, supporting the conclusion that the intermediate-range DD* interaction is dominated by two-pion exchanges and the one-pion exchange contribution is absent. At a quantitative level, the covariant chiral perturbation theory results agree better with the lattice QCD results than their nonrelativistic counterparts, showing the relevance of relativistic corrections in the charm sector.