1,720,982 research outputs found
Towards a complete theory of fermion masses and mixings with SO(3) family symmetry and 5d SO(10) unification
No full textWe construct a complete 4d model of fermion masses and mixings in the Pati-Salam SU(4)SU(2)LSU(2)R framework governed by an SO(3) gauged Family Symmetry. The relevant low energy effective Yukawa operators are constructed so that the SO(3) flavons enter at the simplest possible one-flavon level, with couplings enforced by an additional U(1) × Z2 symmetry. The simplicity of the flavon sector allows the messenger sector to be fully specified, allowing the ultraviolet completion of the model at the 4d renormalizable level. The model predicts approximate tri-bimaximal lepton mixing via the see-saw mechanism with sequential dominance, and vacuum alignment of flavons, with calculable deviations described by the neutrino sum rule. We perform a numerical analysis of the emerging charged fermion spectra and mixings. The 4d model is shown to result from a 5d orbifold GUT model based on SO(3) × SO(10), where small flavon vacuum expectation values (VEVs) originate from bulk volume suppression
Structure and prospects of the simplest SO(10) GUTs
No full textWe recapitulate the latest results on the class of the simplest SO(10) grand unified models in which the GUTscale symmetry breaking is triggered by an adjoint Higgs representation. We argue that the minimal survival approximation traditionally used in the GUT-and seesaw-scale estimates tends to be blind to very interesting parts of the parameter space in which some of the intermediate-scale states necessary for non-supersymmetric unification of the SM gauge couplings can be as light as to leave their imprints in the TeV domain. The stringent minimal-survival-based estimates of the B - L scale are shown to be relaxed by as much as four orders of magnitude, thus admitting for a consistent implementation of the standard seesaw mechanism even without excessive fine-tuning implied by the previous studies. The prospects of the minimal renormalizable SO(10) GUT as a potential candidate for a well-calculable theory of proton decay are discussed in brief. © 2013 AIP Publishing LLC
Towards a new minimal SO(10) unification
No full textWe argue that non-supersymmetric SO(10) models based on a renormalizable Higgs sector in which spontaneous symmetry breaking is triggered by the VEVs of a 45-dimensional adjoint and a 126-dimensional tensor representations can provide a potentially realistic yet relatively simple framework for a future robust estimate of the proton lifetime. Following closely the work [1] we comment on the gauge unification constraints on the B - L breaking scale and show that there are several regions in the parameter space of the minimal model where the seesaw scale in the phenomenologically favoured ballpark of around 1013÷14GeV is consistently supported. © 2012 American Institute of Physics
Minimal flipped SO(10)-U(1) supersymmetric Higgs model
No full textWe investigate the conditions on the Higgs sector that allow supersymmetric SO(10) grand unified theories to break spontaneously to the standard electroweak model at the renormalizable level. If one considers Higgs representations of dimension up to the adjoint, a supersymmetric standard model vacuum requires, in most cases, the presence of nonrenormalizable operators. The active role of Planck-induced nonrenormalizable operators in the breaking of the gauge symmetry introduces a hierarchy in the mass spectrum at the grand unified theory scale that may be an issue for gauge unification and proton decay. We show that the minimal Higgs scenario that allows for a renormalizable breaking to the standard model is obtained by considering flipped SO(10)-U(1) with one adjoint (45H) and two pairs of 16H16 ̄H Higgs representations. We consider a nonanomalous matter content and discuss the embedding of the model in an E6 grand unified scenario just above the flipped SO(10) scale. © 2011 American Physical Society
Light color octet scalars in the minimal SO(10) grand unification
No full textWe analyze the relation between the present (and foreseen) bounds on matter stability and the presence of TeV-scale color octet scalar states in nonsupersymmetric SO(10) grand unification with one adjoint Higgs representation triggering the symmetry breaking. This scenario, discarded long ago due to tree-level tachyonic instabilities appearing in all phenomenologically viable breaking patterns, has been recently revived at the quantum level. By including the relevant two-loop corrections we find a tight correlation between the octet mass and the unification scale which either requires a light color octet scalar within the reach of the LHC or, alternatively, a proton lifetime accessible to the forthcoming megaton-scale facilities. © 2013 American Physical Society
Seesaw scale in the minimal renormalizable SO(10) grand unification
No full textSimple SO(10) Higgs models with the adjoint representation triggering the grand unified symmetry breaking, discarded long ago due to inherent tree-level tachyonic instabilities in the physically interesting scenarios, have been recently brought back to life by quantum effects. In this work we focus on the variant with 45 H⊗126 H in the Higgs sector and show that there are several regions in the parameter space of this model that can support stable unifying configurations with the B-L-breaking scale as high as 1014GeV, well above the previous generic estimates based on the minimal survival hypothesis. This admits for a renormalizable implementation of the canonical seesaw and makes the simplest potentially realistic scenario of this kind a good candidate for a minimal SO(10) grand unification. Last, but not least, this setting is likely to be extensively testable at future large-volume facilities such as Hyper-Kamiokande. © 2012 American Physical Society
The vacuum of the minimal nonsupersymmetric SO(10) unification
No full textWe study a class of nonsupersymmetric SO(10) grand-unified scenarios where the first stage of the symmetry breaking is driven by the vacuum expectation values of the 45-dimensional adjoint representation. Three-decade-old results claim that such a Higgs setting may lead exclusively to the flipped SU(5) - U(1) intermediate stage. We show that this conclusion is actually an artifact of the tree-level potential. The study of the accidental global symmetries emerging in various limits of the scalar potential offers a simple understanding of the tree-level result and a rationale for the drastic impact of quantum corrections. We scrutinize in detail the simplest and paradigmatic case of the 45H 16H Higgs sector triggering the breaking of SO(10) to the standard electroweak model. We show that the minimization of the one-loop effective potential allows for intermediate SU(4)C - SU(2)L - U(1)R and SU(3)c - SU(2)L - SU(2)R - U(1)B-L symmetric stages as well. These are the options favored by gauge unification. Our results, that apply whenever the SO(10) breaking is triggered by 45H, open the path for hunting the simplest realistic scenario of nonsupersymmetric SO(10) grand unification. © 2010 The American Physical Society
Intermediate mass scales in the nonsupersymmetric SO(10) grand unification: A reappraisal
No full textThe constraints of gauge unification on intermediate mass scales in nonsupersymmetric SO(10) scenarios are systematically discussed. With respect to the existing reference studies we include the U(1) gauge mixing renormalization at the one- and two-loop level, and reassess the two-loop beta coefficients. We evaluate the effects of additional Higgs multiplets required at intermediate stages by a realistic mass spectrum and update the discussion to the present day data. On the basis of the obtained results, SO(10) breaking patterns with up to two intermediate mass scales are discussed for potential relevance and model predictivity. © 2009 The American Physical Society
The quantum vacuum of the minimal SO(10) GUT
No full textWe reexamine the longstanding no-go excluding all potentially viable SO(10) →SU(3)c⊗ SU(2)L ⊗ U(1)Y symmetry breaking patterns within the minimal renormalizable non-supersymmetric SO(10) GUT framework featuring the 45-dimensional adjoint representation in the Higgs sector. A simple symmetry argument indicates that quantum effects do change the vacuum structure of the model dramatically. A thorough analysis of the one-loop effective potential reveals that the phenomenologically favoured symmetry breaking chains passing through the SU(4)C ⊗ SU(2)L ⊗ U(1)R or SU(3)c ⊗ SU(2)L ⊗ SU(2)R ⊗ U(1)B-L intermediate stages are, indeed, supported at the quantum level. This brings the class of minimal non-supersymmetric SO(10) GUTs back from oblivion, providing a new ground for a potentially realistic model building. © 2010 IOP Publishing Ltd
A(4) family symmetry and quark-lepton unification
No full textWe present a model of quark and lepton masses and mixings based on A4 family symmetry, a discrete subgroup of an SO(3) flavour symmetry, together with Pati–Salam unification. It accommodates tri-bimaximal neutrino mixing via constrained sequential dominance with a particularly simple vacuum alignment mechanism emerging through the effective D-term contributions to the scalar potential.<br/
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