Half-Skyrmions and the equation of state for compact-star matter

Abstract

The half-skyrmions that appear in dense baryonic matter when skyrmions are put on crystals modify drastically hadron properties in dense medium and affect strongly the nuclear tensor forces, thereby influencing the equation of state (EoS) of dense nuclear and asymmetric nuclear matter. The matter comprising half-skyrmions has vanishing quark condensate but nonvanishing pion decay constant and could be interpreted as a hadronic dual of strong-coupled quark matter. We infer from this observation combined with certain predictions of hidden local symmetry in low-energy hadronic interactions a set of new scaling laws-called "new-BR"-for the parameters in nuclear effective field theory controlled by renormalization-group flow. They are subjected to the EoS of symmetric and asymmetric nuclear matter, and are then applied to nuclear symmetry energies and properties of compact stars. The changeover from the skyrmion matter to a half-skyrmion matter that takes place after the crossover density n(1/2) provides a simple and natural field theoretic explanation for the change of the EoS from soft to stiff at a density above that of nuclear matter required for compact stars as massive as similar to 2.4M(circle dot). Crossover density in the range 1.5n(0) less than or similar to n(1/2) less than or similar to 2.0n(0) was employed, and the possible skyrmion half-skyrmion coexistence or crossover near n(1/2) is discussed. The novel structure of the tensor forces and the EoS obtained with the new-BR scaling is relevant for neutron-rich nuclei and compact-star matter and could be studied in RIB (rare isotope beam) machines.