Deeply bound dibaryon $d^*(2380)$ from meson-exchange saturation $\Delta\Delta$ effective field theory

Abstract

We propose an RG-improved effective-field-theory framework for the deeply bound dibaryon $d^*(2380)$, a $\Delta\Delta$ bound state in the $(J,I)=(3,0)$ ${}^7S_3$ channel. Its binding momentum $\gamma\simeq 320$ MeV gives $\gamma/m_\pi\simeq 2.3$, indicating the need to re-organize the short-range dynamics beyond a formal pionless EFT. We match the large-$N_c$-constrained pionless contact potential to a meson-exchange-saturated contact interaction in which the $\sigma,\rho,\omega$ dynamics are integrated out at the hadronic scale $m_V$, yielding the controlled expansion parameter $\gamma/m_V\simeq 0.42$. Normalizing the contact coupling to the deuteron and substituting the phenomenological CD-Bonn couplings gives $B_{\Delta\Delta}\simeq 96$ MeV. The $\simeq 14\%$ discrepancy from $B_{\rm exp}=84$ MeV is of the natural size of $\mathcal{O}(1/N_c^2)\simeq 11\%$ corrections to the $NN$ potential, confirming compatibility with a controlled EFT expansion organized around the finite-range hadronic scale. As a result, the observed $d^*(2380)$ pole emerges from the virtual state to bound state by using the EFT re-organization in this work.