Equation of state and hybrid star properties with the weakly interacting
  light U-boson in relativistic models
  It has been a puzzle whether quarks may exist in the interior of massive
neutron stars, since the hadron-quark phase transition softens the equation of
state (EOS) and reduce the neutron star (NS) maximum mass very significantly.
In this work, we consider the light U-boson that increases the NS maximum mass
appreciably through its weak coupling to fermions. The inclusion of the U-boson
may thus allow the existence of the quark degrees of freedom in the interior of
large mass neutron stars. Unlike the consequence of the U-boson in hadronic
matter, the stiffening role of the U-boson in the hybrid EOS is not sensitive
to the choice of the hadron phase models. In addition, we have also
investigated the effect of the effective QCD correction on the hybrid EOS. This
correction may reduce the coupling strength of the U-boson that is needed to
satisfy NS maximum mass constraint. While the inclusion of the U-boson also
increases the NS radius significantly, we find that appropriate in-medium
effects of the U-boson may reduce the NS radii significantly, satisfying both
the NS radius and mass constraints well.
