Proton decay and new contribution to 0ν2β decay in SO(10) with low-mass Z′ boson, observable n − n ¯ $$ n-\overline{n} $$ oscillation, lepton flavor violation, and rare kaon decay

Abstract

Proton decay and new contribution to 0ν2β decay in SO(10) with low-mass Z ′ boson, observable n −n oscillation, lepton flavor violation, and rare kaon decay Abstract:In the conventional approach to observable n −n oscillation through PatiSalam intermediate gauge symmetry in SO(10), the canonical seesaw mechanism is also constrained by the symmetry breaking scale M R ∼ M C ≤ 10 6 GeV which yields light neutrino masses several orders larger than the neutrino oscillation data. A method to evade this difficulty is through TeV scale gauged inverse seesaw mechanism which has been recently exploited while predicting experimentally verifiable W ± R , Z R bosons with a new dominant contribution to neutrinoless double beta decay in the W L −W L channel and other observable phenomena, but with proton lifetime far beyond the accessible limits. In the present work, adopting the view that W ± R may be heavy and currently inaccessible to accelerator tests, we show how a class of non-supersymmetric SO(10) models allows a TeV scale Z ′ boson, experimentally testable proton decay along with observable n −n oscillation, and leptoquark gauge boson mediated rare kaon decays without resorting to additional fine-tuning of parameters. The occurrence of Pati-Salam gauge symmetry with unbroken D-parity and two gauge couplings at the highest intermediate scale guarantees precision unification with vanishing GUT-threshold or gravitational corrections on sin 2 θ W (M Z ) prediction in this model. Predictions for neutrinoless double beta decay in the W L − W L channel is analysed in detail including light and heavy sterile neutrino exchange contributions by means of normal and band plots and also by scattered plots while a new formula for half-life is derived. Comparison with available data from various groups by normal and scattered plots reveals how the existing experimental bounds are satisfied irrespective of the mass JHEP01 (2015)045 hierarchy in the light neutrino sector leading to the lower bound on the lightest sterile neutrino mass,M S 1 ≥ 18 ± 2.9 GeV. The model also predicts branching ratios for charged lepton flavor violation verifiable by ongoing search experiments. We also derive new renormalisation group equations constraining the lepto-quark gauge boson mass in the presence of SU(2) L × U(1) R × U(1) B−L × SU(3) C symmetry, specific to the occurrence of extra Z ′ boson, leading to a new lower bound on the lepto-quark gauge boson mass mediating rare kaon decay, M LQ ≥ (1.54±0.06) × 10 6 GeV. We also discuss the symmetry breaking of non-SUSY SO(10) through the well known flipped SU(5) ×Ũ(1) path and show, for the first time, how TeV scale Z ′ is predicted with gauged inverse seesaw ansatz for neutrino masses and substantial lepton flavor and lepton number violations. As a significant new result along this path, we report a successful unification of the two gauge couplings of SU(5) ×Ũ(1) into the single GUT coupling of SO(10).

Standard coupling unification in SO(10), hybrid seesaw neutrino mass and leptogenesis, dark matter, and proton lifetime predictions

“…Extensive investigations in such models have been reported with high intermediate scales [69,[129][130][131][132][133][134][135][136][137][138][139][140][141] and also with TeV scale W R , Z R bosons and verifiable seesaw mechanisms [142][143][144][145][146][147][148][149][150][151][152][153]. Out of a large number of possible models that are predicted from non-SUSY SO(10) [132] fermion mass fit has been investigated only in one class of models with Pati-Salam intermediate symmetry [69,137,139,140] and also including additional vector-like fermions [138].…”

“…The issue of DM has been also addressed with different types of high scale intermediate symmetries and by introducing additional fermions or scalars beyond those needed by extended survival hypothesis [154][155][156][157][158] but without addressing fermion mass fits. The problem of TeV scale W R boson prediction along with DM have been also addressed in non-SUSY SO(10) by invoking external Z 2 symmetry [148] without fitting charged fermion masses as also in a number of other models [132,133,135,136,[141][142][143][144][145][146][147][159][160][161][162]. As there has been no experimental evidence of…”

“…Renormalizable correction. Through renormalizable interaction, the improvement of fermion mass parametrization is also suggested by the introduction of a second 126 H representation [144,146,147]. We denote this and its corresponding components under G 224 as 126 H ⊃ ∆ L (3, 1, 10), ∆ R (1, 3,10), ξ (2, 2, 15), .…”

Vacuum alignment and radiatively induced Fermi scale

“…Instead, the spin-one leptoquarks mediate K L → µ ± e ∓ . Strong experimental limits on these decays lead to a lower bound M > 1.5 · 10 6 GeV on the leptoquark masses [11] translating into the lower bound on the Pati-Salam-unification scale Λ PS 1.9 · 10 6 GeV.…”

High Scale Type-II Seesaw, Dominant Double Beta Decay within Cosmological Bound and LFV Decays in SU(‎5)

“…Despite inverse seesaw, observable double beta decay in the W L − W L channel and the non-QD type neutrino masses remained mutually exclusive until both the RH neutrinos and singlet fermions (S i ) were brought into the arena of LFV and LNV conundrum through the much needed extension of the Higgs sector. The King-Kang [122] mechanism cancelled out the ruling supremacy of canonical seesaw which was profoundly exploited in SO(10) models with the introduction of both the SO(10) Higgs representations 16 H and 126 † H [13,84,[123][124][125][126][127][128] with successful prediction of observable double beta decay in the W L − W L channel [20,87]. Very interestingly, even though high scale type-II seesaw can govern light neutrino masses of any hierarchy, possibility of observable LFV and double beta decay prediction in the W L − W L channel irrespective of light neutrino mass hierarchies has been realized at least theoretically [13,128].…”