How generic is cosmic string formation in SUSY GUTs

TL;DR

Jeannerot, Rocher, and Sakellariadou perform a comprehensive survey of SUSY GUTs with rank up to 8 to determine whether cosmic strings are generically produced after breaking to the Standard Model, assuming standard hybrid inflation and successful leptogenesis. Using maximal regular subgroups and homotopy criteria, they classify all SSB patterns and count those compatible with monopole/domain-wall avoidance, R-parity, and proton lifetime, finding that all cosmologically allowed patterns yield cosmic strings (topological or embedded) at the end of inflation, with possible secondary string networks at lower scales. The results show that for lower-rank groups (rank ≤ 5) strings are unavoidable in the viable patterns, while higher-rank groups frequently predict multiple inflationary eras, each ending in string formation; E6 in particular yields large numbers of defect-allowed patterns that all produce strings. The findings imply that cosmic strings are an intrinsic prediction of realistic SUSY GUTs under these constraints, making their possible CMB signatures and synergy with inflation a critical probe for high-energy physics and cosmology.

Abstract

We study cosmic string formation within supersymmetric grand unified theories. We consider gauge groups having a rank between 4 and 8. We examine all possible spontaneous symmetry breaking patterns from the GUT down to the standard model gauge group. Assuming standard hybrid inflation, we select all the models which can solve the GUT monopole problem, lead to baryogenesis after inflation and are consistent with proton lifetime measurements. We conclude that in all acceptable spontaneous symmetry breaking schemes, cosmic string formation is unavoidable. The strings which form at the end of inflation have a mass which is proportional to the inflationary scale. Sometimes, a second network of strings form at a lower scale. Models based on gauge groups which have rank greater than 6 can lead to more than one inflationary era; they all end by cosmic string formation.