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  • Open Access

Investigating the two-pion exchange of the double charm DD* chiral interactions and Tcc

Hao Xu* and Li-Xiang Ren†

  • *Contact author: xuh2020@nwnu.edu.cn
  • †Contact author: 2023212235@nwnu.edu.cn
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Phys. Rev. D 112, 114003 – Published 4 December, 2025

DOI: https://doi.org/10.1103/gryg-xtt4

Abstract

Under chiral effective field theory, we study the S-wave DD* interactions up to second chiral order at one-loop level, which contain full contact, one-pion-exchange (OPE) and two-pion-exchange (TPE) contributions. Here, we adopt a new subtraction scheme of the two-particle-reducible contributions and attempt different regularization schemes uniquely for the TPE contributions since they are highly divergent on the momentum transfer. Under these schemes, we conclude that, in the I=0 channel, the TPE contribution is repulsive, then the competition between this powerful repulsing TPE and the other two (contact and OPE) results in a quite weak attraction. This explains why Tcc has an extremely small binding energy if treated as the I=0 DD* bound state. This feature resembles that of hidden charm DD¯* as we investigated in previous work [Phys. Rev. D 105, 034013 (2022)], which also interpreted the extremely near-threshold phenomenon of X(3872). In addition, we also solve the Bethe-Salpeter equation with the chiral interactions for a consistency check.

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Phys. Rev. D 112, 114003– Published 4 December, 2025
  • Received 26 September 2025
  • Accepted 12 November 2025
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