Abstract

The LHCb discovery of doubly charm tetraquark Tcc in 2021 sparked significant interest in theoretical investigations of doubly heavy tetraquarks. In our previous lattice QCD investigation (PRL 2021), we have demonstrated that at the unphysically heavy pion masses we work with, the Tcc pole in the DD* scattering amplitude corresponds to a virtual bound pole. It was later pointed out by Du et al., and others that the presence of nonanalyticities arising out of Mandelstam u-channel off-shell pion exchanges, invalidates some of the assumptions we have made in the subthreshold region. In our recent work, we perform a study of quark mass dependence of the amplitudes following two approaches. One based on the vanilla effective range expansion, and the next based on an effective field theory of interactions to describe the DD* scattering that incorporates the one-pion exchange process.