Proton Lifetime and Neutrino Masses from a Fixed-Point String Scale in Type IIB

This paper investigates the low-energy phenomenological consequences of a Type IIB string compactification in which fluxes and nonperturbative effects dynamically stabilize the Kähler volume modulus at a specific fixed point. The resulting scalar potential naturally yields a vacuum energy compatible with the observed dark energy density, without requiring continuous parameter tuning. The stabilized modulus determines the string scale to be approximately 1.2 × 10¹⁶ GeV, which in turn sets the suppression scale for higher-dimensional operators in the Standard Model Effective Field Theory. Dimension-six baryon-number-violating operators suppressed by this scale predict a proton lifetime on the order of 10³⁴ to 10³⁵ years, within the projected sensitivity range of future experiments. Similarly, dimension-five lepton-number-violating operators generate a neutrino mass scale that is slightly below the value inferred from atmospheric neutrino oscillation data, but could be matched through modest ultraviolet enhancements. The analysis demonstrates that a single, dynamically selected modulus value links vacuum energy, proton decay, and neutrino masses in a testable string-theoretic framework.