Nucleon and singly heavy baryons from the QCD instanton vacuum

Abstract

We construct an effective chiral theory for the nucleon, based on the low-energy effective QCD partition function from the QCD instanton vacuum. We fully consider the momentum-dependent dynamical quark mass whose value at the zero virtuality of the quark is determined by the gap equation from the instanton vacuum, $M_0=359$ MeV. The nucleon emerges as a state of $N_c$ valence quarks bound by the pion mean field, which was created self-consistently by the $N_c$ valence quarks. In the large Euclidean time, the classical nucleon mass is evaluated by minimizing the sum of the $N_c$ discrete-level energies and the Dirac-continuum energy: $M_{\text{cl}}=1.2680$ GeV. The pion mean-field solution turns out broader than the local chiral quark-soliton model. The zero-mode quantization furnishes the nucleon with proper quantum numbers such as the spin and isospin. We compute the moment of inertia $I=1.3853$ fm by using the self-consistent mean-field solution, which yields the $\Delta -N$ mass splitting $M_{\Delta-N} =213.67$ MeV. In the same manner, singly heavy baryons can be described as a bound state of the $N_c-1$ valence quarks with the corresponding pion mean field, with the heavy quark regarded as a static color source. The mass splitting of the singly heavy baryons is obtained to be $M_{\Sigma_Q-\Lambda_Q}=206.20$ MeV, which are in good agreement with the experimental data. The effective chiral theory developed in the present work will provide a solid theoretical framework to investigate gluonic observables of both the light and singly heavy baryons.