arXiv subjects

S. F. King

Publications and source records attributed to S. F. King.

At least 91 records · Page 5Linked to original sources

arXiv2006

Spectrum of Higgs particles in the Exceptional Supersymmetric Standard Model

We discuss the spectrum of Higgs bosons in the framework of the exceptional supersymmetric standard model. The presence of a $Z'$ and exotic particles predicted by the exceptional SUSY model allows the lightest Higgs particle to be significantly heavier than in the MSSM and NMSSM. When the mass of the lightest Higgs boson is larger than $135-140 {GeV}$ the heaviest scalar, pseudoscalar and charged Higgs states lie beyond the ${TeV}$ range.

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arXiv2005

Tri-bimaximal neutrino mixing from discrete subgroups of SU(3) and SO(3) family symmetry

It has recently been shown how tri-bimaximal neutrino mixing can be achieved, using the see-saw mechanism with constrained sequential dominance, through the vacuum alignment of a broken non-Abelian gauged family symmetry such as SO(3) or SU(3). Generalising the approach of Altarelli and Feruglio developed for an $A_4$ model we show how the reduction of the underlying symmetry to a discrete subgroup of SO(3) or SU(3) renders this alignment a generic property of such models. This means near tri-bimaximal mixing can be quite naturally accommodated in a complete unified theory of quark and lepton masses.

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arXiv2005

Supersymmetry Parameter Analysis: SPA Convention and Project

High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e+e- linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.

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arXiv2005

Exceptional Supersymmetric Standard Model

We discuss some phenomenological aspects of an $E_6$ inspired supersymmetric standard model with an extra $U(1)_{N}$ gauge symmetry under which right-handed neutrinos have zero charge, allowing a conventional see-saw mechanism. The $μ$ problem is solved in a similar way to the NMSSM, but without the accompanying problems of singlet tadpoles or domain walls. The above exceptional supersymmetric standard model (ESSM) involves the low energy matter content of three 27 representations of $E_6$, which is broken at the GUT scale, and allows gauge coupling unification due to an additional pair of Higgs-like doublets. The ESSM predicts a $Z'$ boson and exotic quarks which, if light enough, will provide spectacular new physics signals at the LHC. We study the LHC phenomenology of the $Z'$ and extra quarks, including their production and decay signatures particular to the ESSM. We also discuss the two-loop upper bound on the mass of the lightest CP-even Higgs boson, and show that it can be significantly heavier than in either the MSSM or the NMSSM.

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arXiv2005

Theory and Phenomenology of an Exceptional Supersymmetric Standard Model

We make a comprehensive study of the theory and phenomenology of a low energy supersymmetric standard model originating from a string-inspired $E_6$ grand unified gauge group. The Exceptional Supersymmetric Standard Model (ESSM) considered here is based on the low energy SM gauge group together with an extra $Z'$ corresponding to an extra $U(1)_{N}$ gauge symmetry under which right--handed neutrinos have zero charge. The low energy matter content of the ESSM corresponds to three 27 representations of the $E_6$ symmetry group, to ensure anomaly cancellation, plus an additional pair of Higgs--like doublets as required for high energy gauge coupling unification. The ESSM is therefore a low energy alternative to the MSSM or NMSSM. The ESSM involves extra matter beyond the MSSM contained in three $5+5^*$ representations of SU(5), plus three SU(5) singlets which carry $U(1)_{N}$ charges, one of which develops a VEV, providing the effective $μ$ term for the Higgs doublets, as well as the necessary exotic fermion masses. We explore the RG flow of the ESSM and examine theoretical restrictions on the values of new Yukawa couplings caused by the validity of perturbation theory up to the Grand Unification scale. We then discuss electroweak symmetry breaking and Higgs phenomenology, and establish an upper limit on the mass of the lightest Higgs particle which can be significantly heavier than in the MSSM and NMSSM, in leading two--loop approximation. We also discuss the phenomenology of the $Z'$ and the extra matter, whose discovery will provide a smoking gun signal of the model.

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arXiv2005

Theory of Neutrinos: A White Paper

During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled ``The Neutrino Matrix'' accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.

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arXiv2005

Lepton flavour violation in realistic non-minimal supergravity models

Realistic effective supergravity models have a variety of sources of lepton flavour violation (LFV) which can drastically affect the predictions relative to the scenarios usually considered in the literature based on minimal supergravity and the supersymmetric see-saw mechanism. We catalogue the additional sources of LFV which occur in realistic supergravity models including the effect of D-terms arising from an Abelian U(1) family symmetry, non-aligned trilinear contributions from scalar F-terms, as well as non-minimal supergravity contributions and the effect of different Yukawa textures. In order to quantify these effects, we investigate a string inspired effective supergravity model arising from intersecting D-branes supplemented by an additional U(1) family symmetry. In such theories the magnitude of the D-terms is predicted, and we calculate the branching ratios for $μ\to eγ$ and $τ\to μγ$ for different benchmark points designed to isolate the different non-minimal contributions. We find that the D-term contributions are generally dangerously large, but in certain cases such contributions can lead to a dramatic suppression of LFV rates, for example by cancelling the effect of the see-saw induced LFV in $τ\to μγ$ models with lop-sided textures. In the class of string models considered here we find the surprising result that the D-terms can sometimes serve to restore universality in the effective non-minimal supergravity theory.

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arXiv2005

Predicting neutrino parameters from SO(3) family symmetry and quark-lepton unification

We show how the neutrino mixing angles and oscillation phase can be predicted from tri-bimaximal neutrino mixing, corrected by charged lepton mixing angles which are related to quark mixing angles via quark-lepton unification. The tri-bimaximal neutrino mixing can naturally originate from the see-saw mechanism via constrained sequential dominance (CSD), where CSD can result from the vacuum alignment of a non-Abelian family symmetry such as SO(3). We construct a realistic model of quark and lepton masses and mixings based on SO(3) family symmetry with quark-lepton unification based on the Pati-Salam gauge group. The atmospheric angle is predicted to be approximately maximal $θ_{23}= 45^\circ$, corrected by the quark mixing angle $θ_{23}^{\mathrm{CKM}}\approx 2.4^\circ$, with the correction controlled by an undetermined phase in the quark sector. The solar angle is predicted by the tri-bimaximal complementarity relation: $θ_{12}+ \frac{1}{\sqrt{2}}\frac{θ_{\mathrm{C}}}{3} \cos (δ- π) \approx 35.26^\circ $, where $θ_{\mathrm{C}}$ is the Cabibbo angle and $δ$ is the neutrino oscillation phase. The reactor angle is predicted to be $θ_{13} \approx \frac{1}{\sqrt{2}}\frac{θ_{\mathrm{C}}}{3}\approx 3.06^\circ$. The MNS neutrino oscillation phase $δ$ is predicted in terms of the solar angle to be $\cos (δ- π) \approx (35.26^\circ - θ_{12}^\circ)/3.06^\circ $. These predictions can all be tested by future high precision neutrino oscillation experiments, thereby probing the nature of high energy quark-lepton unification.

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arXiv2005

Study of theory and phenomenology of some classes of family symmetry and unification models

We review and compare theoretically and phenomenologically a number of possible family symmetries, which when combined with unification, could be important in explaining quark, lepton and neutrino masses and mixings, providing new results in several cases. Theoretical possibilities include Abelian or non-Abelian, symmetric or non symmetric Yukawa matrices, Grand Unification or not. Our main focus is on anomaly-free U(1) family symmetry combined with SU(5) unification, although we also discuss other possibilities. We provide a detailed phenomenological fit of the fermion masses and mixings for several examples, and discuss the supersymmetric flavour issues in such theories, including a detailed analysis of lepton flavour violation. We show that it is not possible to quantitatively and decisively discriminate between these different theoretical possibilities at the present time.

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arXiv2005

Small Yukawa Couplings from Type I String Theory and the Inflationary Solution to the Strong CP and $μ$ Problems

We investigate the origin of phenomenologically interesting small Yukawa couplings in Type I string theory. Utilising the framework of intersecting sets of D9 and orthogonal D5 branes we demonstrate the connection between extra dimensional volumes and Yukawa couplings. For example, we show that extra dimensions with inverse lengths of $10^8$ GeV can lead to $10^{-10}$ Yukawa couplings. String selection rules, arising from the D-Brane setup, impose non-trivial constraints on the set of allowed superpotentials. As a phenomenological application of these results we construct a type I string model of inflationary particle physics which involves small Yukawa couplings of order $10^{-10}$, and simultaneously solves the strong CP and $μ$ problem of the MSSM, via the vacuum expectation value of the inflaton field.

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arXiv2005

Inflationary Solution to the Strong CP and $μ$ Problems

We show that the vacuum expectation value of the inflaton at the Peccei-Quinn axion scale can generate the supersymmetric Higgs mass $μ$ term. This provides an inflationary simultaneous solution to the strong CP problem and the $μ$ problem of the Minimal Supersymmetric Standard Model, and gives a testable prediction for the $μ$ parameter: $μ^2 \approx (0.25-0.5)m_0^2$, where $m_0$ is the soft Higgs scalar mass. Our model involves a very small Yukawa coupling of order $10^{-10}$, which could originate from an extra-dimensional scenario or type I string theory.

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arXiv2004

Theory of Neutrinos

After a brief overview of the present knowledge of neutrino masses and mixing, we summarize what can be learned about physics beyond the standard model from the various proposed neutrino experiments. We also comment on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe as well as what can be learned from some experiments outside the domain of neutrinos.

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arXiv2004

Testing the see-saw mechanism at collider energies

We propose a low energy extension of the Standard Model consisting of an additional gauged $U(1)_{B-L}$ plus three right-handed neutrinos. The lightest right-handed neutrinos have TeV scale masses and may be produced at colliders via their couplings to the $Z_{B-L}$ gauge boson whose mass and gauge coupling is constrained by the out-of-equilibrium condition leading to upper bounds on the right-handed neutrino and $Z_{B-L}$ production cross-sections at colliders. We propose a brane-world scenario which motivates such TeV mass right-handed neutrinos. Our analysis opens up the possibility that the mechanism responsible for neutrino mass is testable at colliders such as the LHC or VLHC.

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arXiv2004

Neutrino Mass Models and Leptogenesis

In this talk we show how a natural neutrino mass hierarchy can follow from the type I see-saw mechanism, and a natural neutrino mass degeneracy from the type II see-saw mechanism, where the bi-large mixing angles can arise from either the neutrino or charged lepton sector. We summarize the phenomenological implications of such natural models, and discuss the model building applications of the approach, focussing on the $SU(3)\times SO(10)$ model. We also show that in such type II models the leptogenesis asymmetry parameter becomes proportional to the neutrino mass scale, in sharp contrast to the type I case, which leads to an upper bound on the neutrino mass scale, allowing lighter right-handed neutrinos and hence making leptogenesis more consistent with the gravitino constraints in supersymmetric models.

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arXiv2004

Electrophobic Lorentz invariance violation for neutrinos and the see-saw mechanism

In this talk we show how Lorentz invariance violation (LIV) can occur for Majorana neutrinos, without inducing LIV in the charged leptons via radiative corrections. Such ``electrophobic'' LIV is due to the Majorana nature of the LIV operator together with electric charge conservation. Being free from the strong constraints coming from the charged lepton sector, electrophobic LIV can in principle be as large as current neutrino experiments permit. On the other hand electrophobic LIV could be naturally small if it originates from LIV in some singlet ``right-handed neutrino'' sector, and is felt in the physical left-handed neutrinos via a see-saw mechanism.

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arXiv2004

A model of cosmology and particle physics at an intermediate scale

We propose a model of cosmology and particle physics in which all relevant scales arise in a natural way from an intermediate string scale. We are led to assign the string scale to the intermediate scale M_* \sim 10^{13} GeV by four independent pieces of physics: electroweak symmetry breaking; the μparameter; the axion scale; and the neutrino mass scale. The model involves hybrid inflation with the waterfall field N being responsible for generating the μterm, the right-handed neutrino mass scale, and the Peccei-Quinn symmetry breaking scale. The large scale structure of the Universe is generated by the lightest right-handed sneutrino playing the role of a coupled curvaton. We show that the correct curvature perturbations may be successfully generated providing the lightest right-handed neutrino is weakly coupled in the see-saw mechanism, consistent with sequential dominance.

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arXiv2004

Electron to Muon Conversion in Electron-Nucleus Scattering as a Probe of Supersymmetry

We suggest that $e\to μ$ conversion in low-energy electron-nucleus scattering is a new and potentially observable indirect signal of supersymmetry and should be searched for in experiment. We estimate the rate for this process in a straightforward calculation taking into account the existing constraint from non-observation of the $μ\to eγ$ decay and find the cross-section to be $σ< 10^{-8} $fb.

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arXiv2004

Sequential Dominance

We review the mechanism of sequential right-handed neutrino dominance proposed in the framework of the type I see-saw mechanism to account for bi-large neutrino mixing and a neutrino mass hierarchy in a natural way. We discuss how sequential dominance may also be applied to the right-handed charged leptons, which alternatively allows bi-large lepton mixing from the charged lepton sector. We review how such sequential dominance models may be upgraded to include type II see-saw contributions, resulting in a partially degenerate neutrino mass spectrum with bi-large lepton mixing arising from sequential dominance. We also summarise the model building applications and the phenomenological implications of sequential dominance.

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