Monopoles, strings, and necklaces in SO(10) and E6.

We employ a variety of symmetry breaking patterns in SO(10) and E₆ Grand Unified Theories to demonstrate the appearance of topological defects including magnetic monopoles, strings, and necklaces. We show that independent of the symmetry breaking pattern, a topologically stable superheavy monopole carrying a single unit of Dirac charge as well as color magnetic charge is always present. Lighter intermediate mass topologically stable monopoles carrying two or three quanta of Dirac charge can appear in SO(10) and E₆ models respectively. These lighter monopoles as well as topologically stable intermediate scale strings can survive an inflationary epoch. We also show the ap- pearance of a novel necklace configuration in SO(10) broken to the Standard Model via SU(4)_c × SU(2)_L × SU(2)_R. It consists of SU(4)_c and SU(2)_R monopoles connected by flux tubes. Necklaces consisting of monopoles and antimonopoles joined together by flux tubes are also identified. Even in the absence of topologically stable strings, a monopole-string system can temporarily appear. This system decays by emitting gravity waves and we provide an example in which the spectrum of these waves is strongly peaked around 10⁻⁴ Hz with Ω_qwh² ≃10⁻¹². This spectrum should be within the detection capability of LISA. [ABSTRACT FROM AUTHOR]