Higgs-portal dark matter from non-supersymmetric strings

Large classes of non-supersymmetric string models equipped with standard-model features have been constructed, but very little of their phenomenology is known. Interestingly, their spectra exhibit scalar fields whose only couplings to observed particles is through a multi-Higgs sector. On the other hand, bottom-up models with Higgs portals offer still an acceptable framework for dark matter. We explore realizations of such Higgs portals in promising heterotic orbifold models without supersymmetry. We find that a sample model includes Higgs vacua that are stable at one-loop, in which the Higgs sector is compatible with particle-physics observations and a scalar can account for the measured dark matter abundance. In such vacua, interesting constraints on the masses of the dark matter candidate and the heavy Higgs sector are uncovered. These compelling results are not limited to string models, as they can be embedded in similarly motivated bottom-up schemes.