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

Motivated by the recent lattice QCD study of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>D</a:mi><a:msup><a:mi>D</a:mi><a:mo>*</a:mo></a:msup></a:math> interaction at unphysical quark masses, we perform a theoretical study of the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mi>D</c:mi><c:msup><c:mrow><c:mi>D</c:mi></c:mrow><c:mrow><c:mo>*</c:mo></c:mrow></c:msup></c:mrow></c:math> 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 <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>D</e:mi><e:msup><e:mi>D</e:mi><e:mo>*</e:mo></e:msup></e:math> 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. Published by the American Physical Society 2024