Nature of Higgs Boson: Little Hierarchy, Vacuum Stability and Electroweak Phase Transition

I will talk about theoretical issues in the Higgs potential of certain new physics models. It is well-known that the Higgs mass term has hierarchy problem. Twin Higgs scenario addresses the little hierarchy problem via global Z2 symmetry. But the origin of the Z2 breaking was unknown. I will discuss radiative Z2 breaking mechanism in twin Higgs, which determines the 125 GeV Higgs mass via fully radiative symmetry breaking. Then regarding to the Higgs quartic term, I will talk about the possible Higgs vacuum instability problem in a class of new physics models: vectorlike fermion model, and discuss its possible solution. Finally, electroweak phase transition strongly depends on the shape of the Higgs potential. I will discuss shape of Higgs potential and electroweak baryogenesis mechanism in a scalar-assisted vectorlike fermion model.