We consider magnetic monopoles and strings that appear in non-supersymmetric $SO(10)$ and $E_6$ grand unified models paying attention to gauge coupling unification and proton decay in a variety of symmetry breaking schemes. The dimensionless string tension parameter $G\mu$ spans the range $10^{ -6}-10^{ -30}$, where $G$ is Newton's constant and $\mu$ is the string tension. We show how intermediate scale monopoles with mass $\sim 10^{ 13}-10^{ 14}$ GeV and flux $\lesssim 2.8\times 10^{ -16}$ ${ \mathrm{ cm}^{ -2}\mathrm{ s}^{ -1}\mathrm{ sr}^{ -1}}$, and cosmic strings with $G\mu \sim 10^{ -11}-10^{ -10}$ survive inflation and are present in the universe at an observable level. We estimate the gravity wave spectrum emitted from cosmic strings taking into account inflation driven by a Coleman-Weinberg potential. The tensor-to-scalar ratio $r$ lies between $0.06$ and $0.003$ depending on the details of the inflationary scenario.
Categories: hep-ph hep-th