Linking light scalar modes with a small positive cosmological constant in string theory

Based on the studies in Type IIB string theory phenomenology, we conjecture that a good fraction of the meta-stable de Sitter vacua in the cosmic stringy landscape tend to have a very small cosmological constant Λ when compared to either the string scale M_S or the Planck scale M_P , i.e., Λ ≪ M_S⁴ ≪ M_P⁴. These low lying de Sitter vacua tend to be accompanied by very light scalar bosons/axions. Here we illustrate this phenomenon with the bosonic mass spectra in a set of Type IIB string theory flux compactification models. We conjecture that small Λ with light bosons is generic among de Sitter solutions in string theory; that is, the smallness of Λ and the existence of very light bosons (may be even the Higgs boson) are results of the statistical preference for such vacua in the landscape. We also discuss a scalar field ϕ³/ϕ⁴ model to illustrate how this statistical preference for a small Λ remains when quantum loop corrections are included, thus bypassing the radiative instability problem. © The Authors.