Speaker
Description
Neutron stars are high-density stellar objects that remain after a supernova explosion. Their central density exceeds the nuclear density, and various states are thought to appear in their interiors that do not appear in ordinary nuclei, such as superfluid states of neutrons and protons, quark deconfinement and hyperon mixing. These states have a strong influence on the neutrino emission process, which is the main cooling process in neutron stars, and on the thermal history of neutron stars. Comparison of neutron star temperature observations with cooling calculations can constrain the internal state of neutron stars.
We have calculated the cooling of neutron stars by constructing a model in which quark matter in a colour superconducting state in the core. The colour superconducting state may have several pairings depending on the quark colour and flavour degrees of freedom, and we assume that the CFL (Colour Flavour Locked) or 2SC (Two-Flavour Colour Superconducting) phases appear. We also introduced quark-hadron continuity, where the ${}^3P_2$ superfluidity of neutrons in the hadron phase is taken over by unpaired $d$ quarks in the 2SC phase, and included that state (2SC+<$dd$> phase) in the cooling calculations. The results show that the cooling curves of neutron stars with the 2SC+<$dd$> phase are located in a higher temperature range than those with the 2SC phase and are similar to the CFL phase. According to these results, it can be concluded that the 2SC+<$dd$> phase can be realised in low-temperature neutron stars.
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