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S. F. King

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

At least 163 records · Page 9Linked to original sources
arXiv1999

F-term Hybrid Inflation in Effective Supergravity Theories

We show that a particular class of effective low energy supergravity theories motivated by string theory can provide a promising framework for models of hybrid inflation in which the potential energy which drives inflation originates from the F-term of the effective supergravity theory. In the class of models considered the inflaton is protected from receiving mass during inflation by a generalisation of the Heisenberg symmetry present in no-scale supergravity models. The potential during inflation takes the positive definite form $V\sim |F_S|^2 + |F_T|^2 -3$, which allows the possibility that $V\ll m_{3/2}^2 M_P^2$ through the cancellation of the positive dilaton and moduli contribution against the negative term. We discuss a toy example where this is realised, then describe the application of this result to realistic models focusing on a particular example in which the $μ$ problem and the strong CP-problem are addressed.

hep-ph↗
arXiv1999

A Next-to-Minimal model of Hybrid Inflation in Effective Supergravity Theories

We propose a model of inflation based on a simple variant of the NMSSM, called $ϕ$NMSSM where the additional singlet $ϕ$ plays the role of the inflaton in hybrid (or inverted hybrid) type models. The $ϕ$NMSSM solves the $μ$ problem of the MSSM via the vacuum expectation value of the gauge singlet N, but also solves the strong CP problem through an approximate Peccei-Quinn symmetry. The potential energy which drives inflation originates from the F-term of the effective supergravity theory which result from a generic string theory. In the class of models considered the inflaton is protected from receiving mass during inflation by a Heisenberg symmetry, avoiding the $η$ problem.

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arXiv1999

Naturalness Implications of LEP Results

We analyse the fine-tuning constraints arising from absence of superpartners at LEP, without strong universality assumptions. We show that such constraints do not imply that charginos or neutralinos should have been seen at LEP, contrary to the usual arguments. They do however imply relatively light gluinos $(m_{\tilde g} \lsim 350 GeV)$ and/or a relation between the soft-breaking SU(3) gaugino mass and Higgs soft mass $m_{H_U}$. The LEP limit on the Higgs mass is significant, especially at low $\tan β$, and we investigate to what extent this provides evidence for both a lighter gluino and correlations between soft masses.

hep-ph↗
arXiv1998

Bi-Maximal Neutrino Mixing in the MSSM with a Single Right-Handed Neutrino

We discuss neutrino masses in the framework of a minimal extension of the minimal supersymmetric standard model (MSSM) consisting of an additional single right-handed neutrino superfield $N$ with a heavy Majorana mass $M$, which induces a single light see-saw mass $m_{ν_3}$ leaving two neutrinos massless at tree-level. This trivial extension to the MSSM may account for the atomospheric neutrino data via $ν_μ\to ν_τ$ oscillations by assuming a near maximal mixing angle $θ_{23}\sim π/4$ and taking $Δm_{23}^2 \sim m_{ν_3}^2 \sim 2.5\times 10^{-3} eV^2$. In order to account for the solar neutrino data we appeal to one-loop radiative corrections involving internal loops of SUSY particles, which we show can naturally generate an additional light neutrino mass $m_{ν_{2}}\sim 10^{-5} eV$ again with near maximal mixing angle $θ_{12}\sim π/4$. The resulting scheme corresponds to so-called ``bi-maximal'' neutrino mixing involving ``just-so'' solar oscillations.

hep-ph↗
arXiv1998

Atmospheric and Solar Neutrinos with a Heavy Singlet

We follow a minimalistic approach to neutrino masses, by introducing a single heavy singlet $N$ into the standard model (or supersymmetric standard model) with a heavy Majorana mass $M$, which couples as a single right-handed neutrino in a Dirac fashion to leptons, and induces a single light see-saw mass $m_ν\sim 5\times 10^{-2} eV$, leaving two neutrinos massless. This trivial extension to the standard model may account for the atomospheric neutrino data via $ν_μ\to ν_τ$ oscillations with near maximal mixing angle $θ_{23}\sim π/4$ and $Δm_{μτ}^2 \sim 2.5\times 10^{-3} eV^2$. In order to account for the solar neutrino data the model is extended to SUSY GUT/ string-inspired type models which can naturally yield an additional light tau neutrino mass $m_{ν_τ}\sim few \times 10^{-3} eV$ leading to $ν_{e L}\to (\cos θ_{23}ν_{μL} -\sin θ_{23}ν_{τL})$ oscillations with $Δm_{e1}^2\sim 10^{-5} eV^2$ and a mixing angle $\sin^2 2 θ_1 \approx 10^{-2}$ in the correct range for the small angle MSW solution to the solar neutrino problem. The model predicts $ν_{e L}\to (\sin θ_{23}ν_{μL} +\cos θ_{23}ν_{τL})$ oscillations with a similar angle but a larger splitting $Δm_{e2}^2 \sim 2.5\times 10^{-3} eV^2 $.

hep-ph↗
arXiv1998

Dilaton Stabilisation in $D$-term Inflation

Dilaton stabilisation is usually considered to pose a serious obstacle to successful $D$-term inflation in superstring theories. We argue that the physics of gaugino condensation is likely to be modified during the inflationary phase in such a way as to enhance the gaugino condensation scale. This enables dilaton stabilisation during inflation with the $D$-term still dominating the vacuum energy at the stable minimum.

hep-ph↗
arXiv1998

Lepton Flavour Violation in String-Inspired Models

Lepton flavour violation has been proposed as a significant test of supersymmetric unification. Here we show that such signals are also a generic feature of supersymmetric string unified models in which there is no simple unified gauge group. In realistic models of this kind which involve third family Yukawa unification and large values of $\tan β$, there are generally heavy right-handed (singlet) neutrinos of intermediate mass $M_ν$, whose couplings violate lepton flavour. To illustrate these effects we calculate the rates for $μ\to e γ$ and $τ\to μgamma$ in the minimal supersymmetric $SU(4)\times SU(2)\times SU(2)$ model. Including only the minimum irreducible contributions, we find that both rates are enhanced relative to similar models with low $\tan β$, with $τ\to μgamma$ providing a decisive test of such models in the near future.

hep-ph↗
arXiv1998

Soft Masses in Strong Unification

We examine the infra-red structure of soft supersymmetry breaking masses of the squarks and sleptons in supersymmetric (SUSY) strong unification schemes where $α_{GUT}\sim 0.2-1$. We show that combinations of soft masses approach fixed points which leads to very simple predictions for soft masses at the intermediate scale. The assumption that the high energy gaugino mass $M_{1/2}$ dominates over the soft scalar masses leads to a strong suppression of flavour changing neutral currents, and a low energy SUSY spectrum which is simply predicted in terms of two parameters, namely $α_{GUT}$ and $M_{1/2}$. Due to the quickly falling gauge couplings beneath the high energy scale, the low energy spectrum has a characteristic ``scalar dominated'' signature quite unlike the standard gaugino dominated MSSM where the right-handed sleptons are predicted to be rather light. We also examine the new sources of flavour changing expected in such models, and in particular show that the flavour violation coming from the D-term of a $U(1)_X$ gauged family symmetry may be reduced to an acceptable level.

hep-ph↗
arXiv1998

A Next-to-Minimal Supersymmetric Model of Hybrid Inflation

We propose a model of inflation based on a simple variant of the NMSSM, called $ϕ$NMSSM, where the additional singlet $ϕ$ plays the role of the inflaton in hybrid (or inverted hybrid) type models. As in the original NMSSM, the $ϕ$NMSSM solves the $μ$ problem of the MSSM via the VEV of a gauge singlet $N$, but unlike the NMSSM does not suffer from domain wall problems since the offending $Z_3$ symmetry is replaced by an approximate Peccei-Quinn symmetry which also solves the strong CP problem, and leads to an invisible axion with interesting cosmological consequences. The PQ symmetry may arise from a superstring model with an exact discrete $Z_3 \times Z_5$ symmetry after compactification. The model predicts a spectral index $n=1$ to one part in $10^{12}$.

hep-ph↗
arXiv1998

A Next-to-Minimal Supersymmetric Model of Hybrid Inflation

In this talk we discuss a model of inflation based on a simple variant of the NMSSM, called $ϕ$NMSSM \cite{phiNMSSM}, where the additional singlet $ϕ$ plays the role of the inflaton in hybrid (or inverted hybrid) type models. As in the original NMSSM, the $ϕ$NMSSM solves the $μ$ problem of the MSSM via the VEV of a gauge singlet $N$, but unlike the NMSSM does not suffer from domain wall problems since the offending $Z_3$ symmetry is replaced by an approximate Peccei-Quinn symmetry which also solves the strong CP problem, and leads to an invisible axion with interesting cosmological consequences. The model predicts a spectral index $n=1$ to one part in $10^{12}$.

hep-ph↗
arXiv1997

Minimal Supersymmetric $SU(4) \times SU(2)_L \times SU(2)_R$

We present a minimal string-inspired supersymmetric $SU(4) \times SU(2)_L \times SU(2)_R$ model, and provide a detailed analysis of the symmetry breaking potential in this model, based on a generalisation of that recently proposed by Dvali, Lazarides and Shafi. The model contains a global U(1) R-symmetry and reduces to the MSSM at low energies. However it improves on the MSSM since it explains the magnitude of its $μ$ term and gives a prediction for $\tan β\simeq m_t/m_b$. It also predicts an essentially stable proton, and contains both `cold' and `hot' dark matter candidates. A period of hybrid inflation above the symmetry breaking scale is also possible in this model. Finally it suggests the existence of `heavy' charge $\pm e/6$ (colored) and $\pm e/2$ (color singlet) states.

hep-ph↗
arXiv1997

Challenges for Inverted Hybrid Inflation

Inverted hybrid inflation (in which the inflaton field slowly rolls away from the origin, giving a spectral index $n\lsim 1$) is an appealing variant of the more usually studied hybrid model. Analysing the model alongside the ordinary hybrid case, we show that, in order to provide the correct density perturbations consistent with the COBE measurements, the dimensionless coupling constants of the inverted hybrid potential must be very small indeed. For example, the quartic coupling in a typical such potential is found to be $\lsim 10^{-12}$. A supersymmetric model of inverted hybrid inflation, which does not involve the troublesome quartic coupling is found to lead to a potential which is unbounded from below.

hep-ph↗
arXiv1997

String Unification, Spaghetti Diagrams and Infra-Red Fixed Points

The minimal supersymmetric standard model (MSSM), is perhaps the leading candidate for new physics beyond the standard model, but it encounters difficulties with string gauge unification and in addition does not shed any light on the question of fermion masses. We consider a scenario in which the MSSM is valid up to an energy scale of 10^16 GeV, but that above this scale the theory is supplemented by extra vector-like representations of the gauge group, plus a gauged U(1)_X family symmetry. In our approach the extra heavy matter above the scale 10^16 GeV is used in two different ways: (1) to allow (two-loop) gauge coupling unification at the string scale; (2) to mix with quarks, leptons and Higgs fields via spaghetti diagrams and so lead to phenomenologically acceptable Yukawa textures. We determine the most economical models in which the extra matter can satisfy both constraints simultaneously. We then give a general discussion of the infra-red fixed points of such models, pointing out the conditions for infra-red stability, then discuss two semi-realistic examples: a Higgs mixing model, and a quark mixing model.

hep-ph↗
arXiv1997

Leptoquarks in SUSY Unified Models and the HERA Events

Motivated by the recent HERA events which are consistent with a possible leptoquark interpretation, we discuss the prospects for including additional light colour triplets and anti-triplets in the spectrum of supersymmetric unified theories. We focus on a particular string-inspired Pati-Salam model, and propose a simple mechanism by which a light colour triplet of charge -1/3 plus anti-triplet of charge 1/3, may have a mass of order 200 GeV, with one of the new states having leptoquark couplings and with proton decay suppressed. We also discuss possible scenarios for gauge unification in such a model.

hep-ph↗
arXiv1997

Infra-Red Stable Fixed Points of Yukawa Couplings in Supersymmetric Models

We provide the solutions of the fixed point conditions of the Yukawa sector for a large class of N=1 supersymmetric theories including the minimal and next-to-minimal supersymmetric standard models and their grand unified and other extensions. We also introduce a test which can discriminate between infra-red stable, infra-red unstable and saddle point solutions, and illustrate our methods with the example of the next-to-minimal supersymmetric standard model. We show that in this case, the fixed point prediction of the top quark mass is equivalent to that of the minimal supersymmetric standard model, supporting previous numerical analyses.

hep-ph↗
arXiv1997

Yukawa Textures from Family Symmetry and Unification

In this letter, we show how the combination of both a gauged U(1)_X family symmetry and an extended vertical gauge symmetry in a single model, allows for the presence of additional Clebsch texture zeroes in the fermion mass matrices. This leads to new structures for the textures, with increased predictivity, as compared to schemes with enhanced family symmetries only. We illustrate these ideas in the context of the Pati-Salam gauge group SU(4)xSU(2)_LxSU(2)_R$ supplemented by a U(1)_X gauged family symmetry. In the case of symmetric mass matrices, two of the solutions of Ramond, Roberts and Ross that may not be obtained by family symmetries only, are accurately reproduced. For non-symmetric textures, new structures arise in models of this type. To distinguish between the solutions in this latter case, we performed a numerical fit to the charged fermion mass and mixing data. The best solution we found allows a fit with a total chi^2 of 0.39, for three degrees of freedom.

hep-ph↗
arXiv1997

Yukawa Textures in String Unified Models With SU(4)xO(4) Symmetry

We discuss the origin of Yukawa textures in the string-inspired and string derived models based on the gauge group SU(4)xSU(2)_LxSU(2)_R supplemented by a U(1)_X gauged family symmetry. The gauge symmetries are broken down to those of the minimal supersymmetric standard model which is the effective theory below 10^16 GeV. The combination of the U(1)_X family symmetry and the Pati-Salam gauge group leads to a successful and predictive set of Yukawa textures involving two kinds of texture zeroes: horizontal and vertical texture zeroes. We discuss both symmetric and non-symmetric textures in models of this kind, and in the second case perform a detailed numerical fit to the charged fermion mass and mixing data. Two of the Yukawa textures allow a low energy fit to the data with a total chi^2 of 0.39 and 1.02 respectively, for three degrees of freedom. We also make a first attempt at deriving the non - renormalisable operators required for the Yukawa textures from string theory.

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