Primordial perturbations generated by Higgs field and $R^2$ operator
  If the very early Universe is dominated by the non-minimally coupled Higgs
field and Starobinsky's curvature-squared term together, the potential diagram
would mimic the landscape of a valley, serving as a cosmological attractor. The
inflationary dynamics along this valley is studied, model parameters are
constrained against observational data, and the isocurvature perturbation is
evaluated.
