Magnetic moments of the spin- 1/2 doubly charmed baryons in covariant baryon chiral perturbation theory

Inspired by the recent discovery of the Ξcc++ by the LHCb Collaboration, we study the magnetic moments of the spin-1/2 doubly charmed baryons up to the next-to-leading order in covariant baryon chiral perturbation theory with the extended-on-mass-shell renormalization scheme. There are three low energy constants at this order: a1, a2, and ga. The latest lattice QCD simulations allow us to fix a combination of a1 and a2, while the axial-vector coupling ga can be determined in three different ways: by fitting to the lattice QCD data, by the quark model, or by the heavy antiquark diquark symmetry. The magnetic moments of the spin-1/2 doubly charmed baryons, Ξccd and Ξccs, can then be predicted. We compare our results with those obtained in the heavy baryon chiral perturbation theory and other approaches, and point out some inconsistencies between the lattice QCD simulations and the quark model.