A chiral U (3) × U (3) Lagrangian, containing besides the usual meson fields their first radial excitations, is considered. The Lagrangian is derived by bosonization of the Nambu-Jona-Lasinio (NJL) quark model with separable non-local interactions. The spontaneous breaking of chiral symmetry is governed by the NJL gap equation. The first radial excitations of the kaon, K * and ϕ are described with the help of two form factors. The values for the decay widths of the processes

The spectrum of meson and diquark excitations of dense color neutral cold quark matter is investigated in the framework of a 2-flavored Nambu-Jona-Lasinio type model, including a quark µ-and color µ8 chemical potential. It was found out that in the color superconducting (2SC) phase, i.e. at µ > µc = 342 MeV, µ8 aquires rather small values ∼ 10 MeV in order to ensure the color neutrality. In this phase the π-and σ meson masses are evaluated around ∼ 330 MeV. The spectrum of scalar diquarks in the color neutral 2SC phase consists of a heavy (SUc(2)-singlet) resonance with mass ∼ 1100 MeV, four light diquarks with mass 3|µ8|, and one Nambu -Goldstone boson which is in accordance with the Goldstone theorem. Moreover, in the 2SC phase there are five light stable particles as well as a heavy resonance in the spectrum of pseudo-scalar diquarks. In the color symmetric phase, i.e. for µ < µc, a mass splitting of scalar diquarks and antidiquarks is shown to arise if µ = 0, contrary to the case of µ = 0, where the masses of scalar antidiquarks and diquarks are degenerate at the value ∼ 700 MeV. If the coupling strength in the pseudo-scalar diquark channel is the same as in the scalar diquark one (as for QCD-inspired NJL models), then in the color symmetric phase pseudo-scalar diquarks are not allowed to exist as stable particles.

We study a spin-1 single flavor color superconducting phase which results from a color-spin locking (CSL) interaction in two-flavor quark matter. This phase is particularly interesting for compact star cooling applications since the CSL phase may survive under charge neutrality constraints implying a mismatch between up-and down-quark chemical potentials which can destroy the scalar diquark condensate. CSL gaps are evaluated within an NJL model and they are found to be consistent with cooling phenomenology if a density dependent coupling constant is used.

We consider an extended Nambu-Jona-Lasinio model including both (qq ) and ͑qq͒ interactions with two light-quark flavors in the presence of a single ͑quark density͒ chemical potential. In the color superconducting phase of the quark matter the color SU c (3) symmetry is spontaneously broken down to SU c (2). If the usual counting of Goldstone bosons would apply, five Nambu-Goldstone ͑NG͒ bosons corresponding to the five broken color generators should appear in the mass spectrum. Unlike that expectation, we find only three gapless diquark excitations of quark matter. One of them is an SU c (2) singlet; the remaining two form an SU c (2) ͑anti͒doublet and have a quadratic dispersion law in the small momentum limit. These results are in agreement with the Nielsen-Chadha theorem, according to which NG bosons in Lorentz-noninvariant systems, having a quadratic dispersion law, must be counted differently. The origin of the abnormal number of NG bosons is shown to be related to a nonvanishing expectation value of the color charge operator Q 8 reflecting the lack of color neutrality of the ground state. Finally, by requiring color neutrality, two massive diquarks are argued to become massless, resulting in a normal number of five NG bosons with the usual linear dispersion laws.

We calculate the mass spectra of the pseudoscalar and scalar meson nonets in the Nambu-Jona-Lasinio model with the 't Hooft interaction. We obtain satisfactory result for the pseudoscalar mesons. For the scalar mesons, the 't Hooft interaction somewhat increases the values of the masses. However, it is not sufficient to explain the whole scalar mass spectrum. The situation could be improved for the σ and f 0 mesons through mixing with the glueball state. For the description of the masses of a 0 and K * 0 mesons, it is necessary to involve the other models. The strong decay widths of the scalar mesons are described.