Mass spectrum of spin-one hadrons in dense two-color QCD: Novel predictions by extended linear sigma model

We construct an extended version of the linear sigma model in such a way as to describe spin-1 hadrons as well as spin-0 hadrons in two-color QCD (QC₂D ) by respecting the Pauli-Gürsey S U (4 ) symmetry. Within a mean-field approximation, we therefrom examine a mass spectrum of the spin-1 hadrons at finite quark chemical potential (μ_q) and zero temperature. Not only mean fields of scalar mesons and scalar-diquark baryons but also of vector mesons and vector-diquark baryons are incorporated. As a result, we find that, unless all of those four types of mean fields are taken into account, neither lattice result for the critical μ_q that corresponds to the onset of baryon superfluidity nor for μ_q dependence of the pion mass can be reproduced. We also find that a slight suppression of the ρ meson mass in the superfluid phase, which was suggested by the lattice simulation, is reproduced by subtle mixing effects between spin-0 and spin-1 hadrons. Moreover, we demonstrate the emergence of an axial-vector condensed phase and possibly of a vector condensed phase by identifying the values of μ_q at which the corresponding hadron masses vanish. The possible presence of isotriplet 1^- diquarks that may be denoted by a tensor-type quark bilinear field is also discussed.