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

Abstract

We employ a variety of symmetry breaking patterns in SO(10) and E 6 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 E 6 models respectively. These lighter monopoles as well as topologically stable intermediate scale strings can survive an inflationary epoch. We also show the appearance 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 gw h 2 ≃ 10 −12. This spectrum should be within the detection capability of LISA.

Threshold effects in SO(10) models with one intermediate breaking scale

“…Note that there also exist bounds on M I , such as righthanded neutrino masses in the type I seesaw mechanism or leptogenesis [100][101][102][103][104][105]. Other possible experimental constraints on GUTs may come from neutron-antineutron oscillations [106][107][108][109][110] induced by the breaking of B − L or topological defects [39,78,86,[111][112][113][114][115][116][117][118] from the breaking of some of the symmetries considered. The stability of these topological defects varies between different models, making some more problematic than others.…”

Particles and the Universe

“…Alternatively, a more moderate inflation such as thermal inflation [34], associated with a phase transition occurring at a temperature of the order of the electroweak scale, can dilute them to an acceptable, but possibly measurable level. Cosmic strings from GUTs [35], on the other hand, can generate gravity waves [36], which will be possibly measurable [24,37,38] by future experiments. Finally, domain walls are [33] catastrophic and GUTs should be constructed so that they avoid them (see e.g.…”

$$^3$$He Universe 2020

“…The other composite objects can be constructed and pinned by nafen strands, including nexus (monopole or hedgehog, which connects two or more strings [74]), necklaces [75] and lattices of composite objects [68,69]. But at the moment these analogs of Nambu monopoles [76] and their further extensions are still not resolved in NMR experiments.…”