Hidden sector monopole, vector dark matter and dark radiation with Higgs
  portal
  We show that the 't Hooft-Polyakov monopole model in the hidden sector with
Higgs portal interaction makes a viable dark matter model, where monopole and
massive vector dark matter (VDM) are stable due to topological conservation and
the unbroken subgroup $U(1)_X$. We show that, even though observed CMB data
requires the dark gauge coupling to be quite small, a right amount of VDM
thermal relic can be obtained via $s$-channel resonant annihilation for the
mass of VDM close to or smaller than the half of SM higgs mass, thanks to Higgs
portal interaction. Monopole relic density turns out to be several orders of
magnitude smaller than observed dark matter relic density. Direct detection
experiments, particularly, the projected XENON1T experiment, may probe the
parameter space where the dark Higgs is lighter than $\lesssim 60 {\rm GeV}$.
In addition, the dark photon associated with unbroken $U(1)_X$ contributes to
the radiation energy density at present, giving $\Delta N_{\rm eff}^\nu \sim
0.1$ as the extra relativistic neutrino species.
