  Thermal evolution of neutron stars (NSs) is studied as a probe of physics
beyond the standard model. We first review the standard cooling theory of NSs
in detail, with an emphasis on the roles of nucleon superfluidity. Then we
discuss non-standard evolution with axion and dark matter (DM); axion
production enhances the cooling while DM accretion leads to heating of NSs. To
evaluate the effect of DM heating, we need to compare it to the rotochemical
heating, which is caused by the out-of-equilibrium beta processes in a NS. In
the dissertation, we also investigate the rotochemical heating in the presence
of both neutron and proton superfluidity.
