A heterotic standard model

Within the context of the E8×E8 heterotic superstring compactified on a smooth Calabi-Yau threefold with an SU(4) gauge instanton, we show the existence of simple, realistic N=1 supersymmetric vacua that are compatible with low-energy particle physics. The observable sector of these vacua has gauge group SU(3)C×SU(2)L×U(1)Y×U(1)B-L, three families of quarks and leptons, each with an additional right-handed neutrino, two Higgs-Higgs conjugate pairs, a small number of uncharged moduli and no exotic matter. The hidden sector contains non-Abelian gauge fields and moduli. In the strong coupling case there is no exotic matter, whereas for weak coupling there are a small number of additional matter multiplets in the hidden sector. The construction exploits a mechanism for “splitting” multiplets. The minimal nature and rarity of these vacua suggest the possible theoretical and experimental relevance of spontaneously broken U(1)B-L gauge symmetry and two Higgs-Higgs conjugate pairs. The U(1)B-L symmetry helps to naturally suppress the rate of nucleon decay.