This thesis focuses on the theoretical foundation of the Standard Model valid up to the Planck
scale based on the current experimental facts from the Large Hadron Collider. The thesis
consists of two themes: (1) to open up a new window of the Higgs inflation scenario and (2) to
explore a new solution to the naturalness problem in particle physics. In the first area on
the Higgs inflation scenario the author successfully improves a large value problem on a
coupling constant relevant to the Higgs mass in the Standard Model in which the coupling value
of the order of 105 predicted in a conventional scenario is reduced to the order of 10. This
result makes the Higgs inflation more attractive because the small value of coupling is natural
in the context of ultraviolet completion such as string theory. In the second area the author
provides a new answer to the naturalness problem of why the cosmological constant and the
Higgs mass are extremely small compared with the Planck scale. Based on the baby universe
theory originally proposed by Coleman the smallness of those quantities is successfully
explained without introducing any additional new particles relevant at the TeV energy scale.
