Embedded defects and symmetry breaking in flipped SU(5)

We explicitly show the analogy between the symmetry-breaking scheme for the GUT flipped SU(5) with that of the Weinberg-Salam theory of electroweak interactions. This allows us to construct the embedded defect spectrum of the flipped SU(5) theory. We find that the spectrum consists of twelve gauge-equivalent unstable leptoquark strings, which are analogous to W strings in electroweak theory, and another string that is gauge inequivalent to the leptoquark strings, which we call the ''V string. The V string is analogous to the Z string of electroweak theory, correspondingly admitting a stable semilocal limit. Using data on the running coupling constants we indicate that in the nonsupersymmetric case V strings can be stable for part of the physically viable parameter space. Cosmological consequences are briefly discussed.