Gravitational Waves and Proton Decay: Complementary Windows into Grand Unified Theories

Abstract

Proton decay is a smoking gun signature of Grand Unified Theories (GUTs). Searches by Super-Kamiokande have resulted in stringent limits on the GUT symmetry breaking scale. The largescale multipurpose neutrino experiments DUNE, Hyper-Kamiokande and JUNO will either discover proton decay or further push the symmetry breaking scale above 10 16 GeV. Another possible observational consequence of GUTs is the formation of a cosmic string network produced during the breaking of the GUT to the Standard Model gauge group. The evolution of such a string network in the expanding Universe produces a stochastic background of gravitational waves which will be tested by a number of gravitational wave detectors over a wide frequency range. We demonstrate the non-trivial complementary between the observation of proton decay and gravitational waves produced from cosmic strings in determining SO(10) GUT breaking chains. We show that such observations could exclude SO(10) breaking via flipped SU (5) × U (1) or standard SU (5), while breaking via a Pati-Salam intermediate symmetry, or standard SU (5) × U (1), may be favoured if a large separation of energy scales associated with proton decay and cosmic strings is indicated.

Metastable strings and dumbbells in supersymmetric hybrid inflation

“…Different string models have been compared in [35]. The possible connection of the NANOGrav results with GUT models and high-scale leptogenesis has also been studied in [36][37][38][39], and effects of low-scale leptogenesis on the SGWB were considered in [40]. Note that, independent of grand unification, a SGWB form a cosmic string network is a very interesting and well motivated signature of physics beyond the Standard Model [41][42][43][44].…”

Gravitational wave complementarity and impact of NANOGrav data on gravitational leptogenesis

“…Most distinguishable feature of GW emission from cosmic string is prediction of a strong signal across a wide range of frequency which has triggered a growing interest in this JHEP05(2021)211 field [76][77][78][79][80][81][82][83][84][85][86]. This also includes recent studies to probe GUT [87,88], high scale leptogenesis [89], low scale leptogenesis [90]. Unequivocally, GW probe of BSM models has become more interesting after the new NANOGrav analysis of 12.5 yrs pulsar timing data [91] which reports a strong evidence for a stochastic common-spectrum process and may be interpreted as a GW signal at frequency f ∼ 1/yr.…”

Confronting SO(10) GUTs with proton decay and gravitational waves

“…All breaking chains from SO (10) to G SM are listed in table 1 and 2. In our previous paper [24], we classified these chains into four categories: The formation of topological defects is ubiquitous in Grand Unified Theories. These defects are formed during the breaking of a larger gauge symmetry G I to a smaller one, G I−1 ⊂ G I .…”

“…In our recent paper [24], we demonstrated the non-trivial complementarity between the observation of proton decay and gravitational waves in assessing the viability of SO (10) GUT breaking chains. We showed that future non-observations could exclude SO (10) breaking via flipped SU(5) × U(1) or standard SU (5), while breaking via a Pati-Salam intermediate symmetry [25], or standard SU(5) × U(1), may be favoured.…”

“…In this paper, we expand on the methodology outlined in our previous work [24] and present a detailed and systematic study of the proton decay and gravitational wave predictions of all non-supersymmetric SO (10) breaking chains. We highlight the importance of gauge coupling unification in constraining the GUT and intermediate breaking scales, and consequently, the scale of cosmic string generation and the proton decay rate.…”