The principle of naturalness is a powerful tool for investigating the Universe. This thesis constructs a nonlinear supergravity model, which is guided by the naturalness of small cosmological constant. The application of algebraic constraints makes the contributions from the Higgs sector and the supersymmetry breaking anti-D3-brane to the cosmological constant exactly cancel. This leaves the cosmological constant to be determined by the geometric sector. As a result, a naturally vanishing cosmological constant is obtained statistically, while the electroweak scale emerges naturally from the observed cosmological constant. The phenomenological extension of this model, which couples the Higgs field to ultra-light pseudo-scalars, named the axi-Higgs cosmology model, helps in resolving seve...[ Read more ]

The principle of naturalness is a powerful tool for investigating the Universe. This thesis constructs a nonlinear supergravity model, which is guided by the naturalness of small cosmological constant. The application of algebraic constraints makes the contributions from the Higgs sector and the supersymmetry breaking anti-D3-brane to the cosmological constant exactly cancel. This leaves the cosmological constant to be determined by the geometric sector. As a result, a naturally vanishing cosmological constant is obtained statistically, while the electroweak scale emerges naturally from the observed cosmological constant. The phenomenological extension of this model, which couples the Higgs field to ultra-light pseudo-scalars, named the axi-Higgs cosmology model, helps in resolving several cosmological puzzles by allowing the cosmic evolution of the Higgs VEV. The possibility of a temporary de Sitter universe is also explored under the misalignment mechanism of Kähler modulus.