U(5) Nambu-Jona-Lasinio model with flavor dependent coupling constants: pseudoscalar and scalar mesons masses

TL;DR

This paper extends the flavor-U(5) NJL model by calculating one-loop polarization corrections to flavor-dependent coupling constants, improving predictions for meson masses and revealing the impact of flavor symmetry breaking and quantum mixing.

Contribution

It introduces flavor-dependent coupling constants derived from one-loop corrections in the NJL model, enhancing the accuracy of meson mass predictions and exploring flavor symmetry effects.

Findings

Accurate prediction of pseudoscalar meson masses within 5%

Most scalar meson masses predicted within 10%

Flavor-dependent couplings improve model predictions

Abstract

By considering the background field method we calculate one-loop polarization corrections to the coupling constant of the flavor-U(5) Nambu-Jona-Lasinio (NJL) model with degenerate up and down quarks. They break flavor and chiral symmetries, and they can be written as $G_{ij}^\Gamma (\bar{\psi} \lambda_i \Gamma \psi) ( \bar{\psi} \lambda_j \Gamma \psi)$, for the scalar and pseudoscalar channels ($\Gamma=I , i \gamma_5$) and $i,j = 0,1,...,N_f^2-1$. Therefore, these coupling constants do not introduce further free parameters in the model which amount to five, six or seven in total. Their contributions to different observables are computed. The non-covariant three-dimensional regularization scheme is employed. Besides that, flavor dependence of cutoffs is implemented in an unambiguous way. It turns out that only two UV cutoffs ($\Lambda_f$) are best suitable. Nevertheless, the best results are obtained for nearly flavor-independent cutoffs. A quantum mixing due to the representations of the flavor group leads to different interactions for the quarks and for the meson states, respectively denoted by $G_{ff}$ and $G_{ij}$. This quantum mixing effect is responsible for a lowering of quark effective masses and a slight improvement of predictions of observables. A quite surprisingly good description of almost all the pseudoscalar meson masses (within nearly $5\%$) and most of the scalar meson masses -is obtained within nearly 10$\%$. Some problems to describe light scalar mesons masses still remain. The NJL-gap equations seems to overestimate the heavy quark condensates at the usual mean field level usually adopted for model. In spite of the good description of the meson masses, the pseudoscalar meson weak decay constant cannot be described by the NJL model with relativistic heavy quark propagators without further interactions or effects.