Speaker
Description
The hot neutron star cools down due to the loss of neutrinos produced by the scattering of particles mainly inside the core, which enables us to probe the state of high-density matter through temperature observations. Recent X-ray observations have confirmed the existence of too cold isolated neutron stars beyond the standard cooling scenario without rapid cooling (i.e., minimal cooling scenario). This may imply the existence of exotic particles such as mesons, hyperons, and quarks. Among them, hyperons are considered a powerful candidate for the rapid cooling process known as the hyperon direct Urca process, along with another candidate, the nucleon direct Urca process. However, because of the large uncertainties of baryon superfluidity/superconductivity, whether such rapid cooling can work efficiently as a rapid cooling mechanism is controversial. For instance, if proton superconductivity is strong, both of the direct Urca processes are too suppressed to explain the cold neutron-star observations. We utilize the latest equation of state with the phase of mixed hyperons and Kaon condensation (i.e., Y+K phase), and discuss the impact of Y+K phase on cooling curves, focusing on the role of Kaon Urca process and proton superconductivity.
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