Flavour Structure and Proton Decay in 6D Orbifold GUTs

The breakdown of E 6 gauge symmetry at high energies may lead to supersymmetric (SUSY) models based on the Standard Model (SM) gauge group together with extra U (1) ψ and U (1) χ gauge symmetries. To ensure anomaly cancellation the particle content of these E 6 inspired models involves extra exotic states that generically give rise to non-diagonal flavour transitions and rapid proton decay. We argue that a single discreteZ H 2 symmetry can be used to forbid tree-level flavor-changing transitions, as well as the most dangerous baryon and lepton number violating operators.We present 5D and 6D orbifold GUT constructions that lead to the E 6 inspired SUSY models of this type. The breakdown of U (1) ψ and U (1) χ gauge symmetries that preserves E 6 matter parity assignment guarantees that ordinary quarks and leptons and their superpartners, as well as the exotic states which originate from 27 representations of E 6 survive to low energies. These E 6 inspired models contain two dark-matter candidates and must also include additional TeV scale vectorlike lepton or vectorlike down type quark states to render the lightest exotic quark unstable. We examine gauge coupling unification in these models and discuss their implications for collider phenomenology and cosmology.

Section: D and 6d Orbifold Gut Modelsmentioning

confidence: 99%

E6inspired supersymmetric models with exact custodial symmetry

Nevzorov

2013

“…There are various viable GUTs (see, e.g., [6][7][8][9][10][11][12]), such as models incorporating supersymmetry (SUSY), models with a symmetry group like SO(10), flipped SU(5) models, and models in extra dimensions. Predictions for the lifetime of the nucleon strongly depend on the models and also have large uncertainties.…”

mentioning

confidence: 99%

Search for nucleon decay into charged antilepton plus meson in Super-Kamiokande I and II

Nishino¹,

Abe²,

Hayato³

et al. 2012

101

Searches for a nucleon decay into a charged anti-lepton (e + or µ + ) plus a light meson (π 0 , π − , η, ρ 0 , ρ − , ω) were performed using the Super-Kamiokande I and II data. Twelve nucleon decay modes were searched for. The total exposure is 140.9 kiloton·years, which includes a 91.7 kiloton·year exposure (1489.2 live days) of Super-Kamiokande-I and a 49.2 kiloton·year exposure (798.6 live days) of Super-Kamiokande-II. The number of candidate events in the data was consistent with the atmospheric neutrino background expectation. No significant evidence for a nucleon decay was observed in the data. Thus, lower limits on the nucleon partial lifetime at 90% confidence level were obtained. The limits range from 3.6 × 10 31 to 8.2 × 10 33 years, depending on the decay modes.

“…For larger GUT groups such as SO (10), however, the 5D case turns out not to be a minimal setup, because a usual Higgs mechanism is required for a further breaking to the SM gauge group or unwanted massless modes of extra components of gauge fields must get massive [11]. In contrast, the 6D case has drawn more attention because it is more economic to obtain the SM gauge group directly from a large GUT group [12,13] and there is more freedom to locate the SM fields for satisfying the experimental requirements such as the flavor structure [14] and the proton longevity [15]. We may even regard the 6D orbifold GUTs as an effective theory of describing (heterotic) string compactifications as an intermediate GUT [16] with the hope to identify the remnants of string theory within the 6D orbifold field theory.…”

Section: Introductionmentioning

confidence: 99%

Gauge coupling unification in six dimensions

Lee

2007

We compute the one-loop gauge couplings in six-dimensional non-Abelian gauge theories on the T 2 /Z 2 orbifold with general GUT breaking boundary conditions. For concreteness, we apply the obtained general formulae to the gauge coupling running in a 6D SO(10) orbifold GUT where the GUT group is broken down to the standard model gauge group up to an extra U (1). We find that the one-loop corrections depend on the parity matrices encoding the orbifold boundary conditions as well as the volume and shape moduli of extra dimensions. When the U (1) is broken by the VEV of bulk singlets, the accompanying extra color triplets also affect the unification of the gauge couplings. In this case, the B − L breaking scale is closely linked to the compactification scales for maintaining a success of the gauge coupling unification.