Mesons and diquarks in neutral color superconducting quark matter with β equilibrium

The spectrum of meson and diquark excitations in cold color superconducting (2SC) quark matter is investigated under local color and electric neutrality constraints with {beta} equilibrium. A two-flavored Nambu-Jona-Lasinio-type model including baryon {mu}{sub B}, color {mu}{sub 8}, and electric {mu}{sub Q} chemical potentials is used. The contribution from free electrons to the free energy is added to take into account the {beta} equilibrium. The sensitivity of the model to the tuning of the interaction constants in the diquark (H) and quark-antiquark (G) channels is examined for two different parametrization schemes by choosing the ratio H/G to be 3/4 and 1, respectively. The gapless neutral color superconductivity is realized at H=3G/4, and the gapped neutral color superconductivity at H=G. It is shown that color and electrical neutrality together with {beta} equilibrium lead to a strong mass splitting within the pion isotriplet in the 2SC phase (both gapped and gapless), in contrast with non-neutral matter. The {pi}- and {sigma}-meson masses are evaluated to be {approx}300 MeV. It is also shown that the properties of the physical SU(2){sub c}-singlet diquark excitation in the 2SC ground state vary for different parametrization schemes. Thus, for H=3G/4 one finds a heavy resonance with mass {approx}1100 MeVmore » in the non-neutral (gapped) case, whereas, if neutrality is imposed, a stable diquark with mass {approx}|{mu}{sub Q}|{approx}200 MeV appears in the gapless 2SC environment. For a stronger attraction in the diquark channel (H=G), there is again a resonance (with the mass {approx}300 MeV) in the neutral gapped 2SC phase. Hence, the existence of the stable massive SU(2){sub c}-singlet diquark excitation is a new peculiarity of the gapless 2SC. In addition, the behavior of the diquark mass in vacuum, i.e., at {mu}{sub B}=0, as a function of H has been investigated.« less