Metastable strings and dumbbells in supersymmetric hybrid inflation

Understand

We study symmetry breaking and topological defects in a supersymmetric model with gauge group $\text{U}(2)$, which can be identified with the right-handed part $\text{SU}(2)_R \times \text{U}(1)_{B-L}$ of an extended electroweak symmetry of the Standard Model.

• The model has two phases of hybrid inflation terminated by tachyonic preheating where either monopoles and strings or, alternatively, dumbbells are formed.
• In the first case a stochastic gravitational wave background is predicted in the LIGO-Virgo band, possibly extending to the LISA frequency band and to nanohertz frequencies, which is generated by a metastable cosmic string network.
• In the second case no topological defects survive inflation and no stochastic gravitational wave background is produced.