Emergent chirality and superfluidity of parity-doubled baryons in neutron stars

We propose novel superfluids induced by the parity-doubled baryons. The parity-doubled baryons, i.e., a nucleon N(940) with mass 940 MeV and spin-parity JP=1/2+ and an excited nucleon N∗(1535) with mass 1535 MeV and spin-parity JP=1/2- in vacuum, become degenerate at sufficiently high density where the chiral symmetry is restored. In this study, we extend the conventional U(1) chiral symmetry to the higher dimensional symmetries, dubbed emergent chiral symmetries, including the naive and mirror assignments as their subgroups. Starting with the Lagrangian up to four-point interactions among the neutron n and its chiral partner n∗, neutral components in N and N∗, in pure neutron matter, we investigate the properties of the ground state with a pairing gap generated by the n and n∗ in the mean-field approximation. We find vector-type condensates that induce the dynamical breaking of a new class of internal symmetries, emergent chiral symmetries, as well as the baryon number and the rotational symmetries of the real space, indicating the appearance of massless Nambu-Goldstone bosons consisting of six quarks: emergent pions, superfluid phonons, and magnons, respectively. We also study the fermionic excitation modes at low-energy scales and show that they exhibit a spatial anisotropy of the propagation at the Dirac cone in momentum space. Some phenomenological implications are advocated, shedding new light on the properties of neutron stars.