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

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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 SU(4) symmetry. Within a mean-field approximation, we therefrom examine a mass spectrum of the spin-1 hadrons at finite quark chemical potential (μq) 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 μq that corresponds to the onset of baryon superfluidity nor for μq 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 μq 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. Published by the American Physical Society 2024