Quantum tunneling in the early universe: stable magnetic monopoles from metastable cosmic strings

Abstract We present a novel mechanism for producing topologically stable monopoles (TSMs) from the quantum mechanical decay of metastable cosmic strings in the early universe. In an SO(10) model this mechanism yields TSMs that carry two units (4 π / e ) of Dirac magnetic charge as well as some color magnetic charge which is screened. For a dimensionless string tension parameter Gμ ≈ 10 -9 -10 -5 , the monopoles are superheavy with masses of order 10 15 -10 17 GeV. Monopoles with masses of order 10 8 -10 14 GeV arise from metastable strings for Gμ values from ∼ 10 -22 to 10 -10 . We identify the parameter space for producing these monopoles at an observable level with detectors such as IceCube and KM3NeT. For lower Gμ values the ultra-relativistic monopoles should be detectable at Pierre Auger and ANITA. The stochastic gravitational wave emission arise from metastable strings with Gμ ∼ 10 -9 -10 -5 and should be accessible at HLVK and future detectors including the Einstein Telescope and Cosmic Explorer. An E 6 extension based on this framework would yield TSMs from the quantum mechanical decay of metastable strings that carry three units (6 π / e ) of Dirac magnetic charge.