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Abstract |
Weakly Interacting Massive Particles (WIMPs) in the Universe accumulate in
neutron stars (NSs) through their interactions with ordinary matter, and their
annihilation inside the NS core causes late-time heating. It has been argued
that this heating effect maintains the surface temperature of old NSs to be
a few thousand K, which can be regarded as a smoking gun signature of
dark matter (DM) heating in NSs. This conclusion is, however, drawn based on
the assumption that the beta equilibrium is sustained in NSs throughout
their life, which turns out to be invalid for real pulsars. If a NS is out of beta
equilibrium, then there is another heating effect due to the dissipation of the
excessive energy stored in the imbalance in the chemical potentials, which
may conceal the DM heating effect. In fact, such an “out-of-equilibrium heating”
effect is favored by recent observations. In this talk, we show that the signature
of DM heating can still be detected in old ordinary pulsars even in the presence
of the out-of-beta-equilibrium effect, whereas it is hidden in millisecond pulsars.
We also discuss that an observation of a NS with the surface temperature
lower than a thousand K imposes a stringent limit on a variety of WIMP DM
candidates, such as the electroweak multiplet DM particles. |
