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S. F. King

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

179 records · Page 10Linked to original sources
arXiv1996

String Gauge Unification and Infra-red Fixed Points in MSSM+X Models

In order to achieve gauge unification at the string scale M_X sim 5.10^17 GeV in the minimal supersymmetric standard model (MSSM) it is necessary to add extra gauge non-singlet representations at an intermediate scale M_I<M_X, leading to a class of models which we refer to as MSSM+X models. We perform a detailed analysis of a large class of MSSM+X models and find that the number of (3,1) representations added must be greater than the total of the number of (3,2) and (1,2) representations. Predictions of M_I, M_X and alpha(M_X) are obtained for models with up to 5 extra vector representations than the MSSM\@. Upper bounds on the U(1) string gauge normalisation k_1 and the sum of the squares of the hypercharge assignments of the extra matter are also obtained for the models. We also study the infra-red fixed point behaviour of the top quark Yukawa coupling in a large class of MSSM+X models and find that the low energy MSSM quasi-fixed point prediction of the top quark mass is more likely to be realised in these theories than in the MSSM. In other words the top quark tends to be heavier in MSSM+X models than in the MSSM. The implementation of a U(1)_X family symmetry into MSSM+X models to account for the Standard Model fermion masses is discussed and a particular viable model is presented.

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arXiv1996

Gauge Unification at the String Scale and Fermion Masses

In the context of the minimal supersymmetric standard model (MSSM), we discuss the introduction of exotic matter below the string scale $M_X$ in order to achieve gauge unification at $M_X$ (a constraint of a large class of string models). The possible types of exotic matter that can realise this are investigated and its effect on the top quark mass $m_t$ is presented. The implementation of a theory of fermion masses which utilises the exotic matter is briefly discussed.

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arXiv1996

Anomalous 4-Jet Events at LEP: a Signal of Low Scale Technicolour?

We suggest that the anomalous 4-jet events recently reported by ALEPH may be the first indication of low scale technicolour. According to our interpretation about half of the events are due to resonantly enhanced pair production of charged technipions, of mass around 55 GeV, each decaying into a pair of jets, the other half being due to standard processes. The resonant enhancement is due to a nearby technirho resonance in the mass range 150-200 GeV, leading to hugely enhanced signals at the forthcoming LEP run at $\sqrt{s}=160$ GeV since the CM energy would be closer to the peak of the resonance.

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arXiv1996

Higgs Physics at LEP2

In this report we review the prospects for Higgs physics at LEP2. The theoretical aspects and the phenomenology of Higgs particles are discussed within the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). The experimental search techniques are described and the discovery limits for Higgs bosons in the LEP2 energy range are summarized. In addition, opportunities of detecting Higgs particles in non-minimal extensions of the SM and the MSSM are investigated.

hep-ph↗
arXiv1995

Non-Minimal Supersymmetric Higgs Bosons at LEP2

We discuss the discovery reach of LEP2 for the Higgs sector of a general extension of the MSSM including a single gauge singlet field. This change introduces a new quartic Higgs boson self-coupling which can increase the masses of the CP-even states, and also allows mixing between singlet and non-singlet states which can reduce the couplings of the mass eigenstates to the $Z$. The lightest CP-even Higgs boson is bounded by a parameter $Λ$ which takes a maximum value $Λ_{max}\approx 136-146$ GeV for top mass $150-195$ GeV. We generalise the discussion of the bound to include the entire CP-even spectrum and show how experiment may exclude values of $Λ$ smaller than some $Λ_{min}$. CP-even Higgs boson searches at LEP2 will be able to exclude $Λ_{min}\approx 81-105$ GeV, depending on the machine parameters. We also present exclusion plots in the $m_A-\tanβ$ plane, based on an analysis of CP-even, CP-odd and charged Higgs production processes at LEP2.

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arXiv1995

Unification Constraints in the Next-to-Minimal Supersymmetric Standard Model

We perform a renormalisation group analysis of the next-to-minimal supersymmetric standard model (NMSSM) based on the following constraints: two-loop gauge coupling unification at a variable scale $M_X$, running the gauge couplings through the low energy thresholds; universal soft supersymmetry breaking parameters; correct electroweak symmetry breaking. The phenomenological implications of our results include a standard model-like Higgs boson of mass in the range 70-140 GeV.

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arXiv1995

Resolving the Constrained Minimal and Next-to-Minimal Supersymmetric Standard Models

We perform a detailed analysis of the next-to-minimal supersymmetric standard model (NMSSM), imposing the constraints of two-loop gauge coupling unification, universal soft supersymmetry breaking and the correct pattern of electroweak symmetry breaking. We compare our results with those for the minimal supersymmetric standard model (MSSM) using closely related techniques and, as far as possible, a common set of input and output variables. In general, in the constrained NMSSM, there are much stronger correlations between parameters than in the constrained MSSM, and we map out the allowed parameter space. We also give a detailed discussion of how to resolve the two models experimentally, concentrating primarily on the prospects at LEPII.

hep-ph↗
arXiv1995

Fermion Masses in a Supersymmetric SU(4)xSU(2)_LxSU(2)_R Model

We calculate quark and lepton masses and quark mixing angles in the framework of a supersymmetric SU(4)$\otimes$SU(2)$_L\otimes$SU(2)$_R$ model where the gauge group is broken at 10$^{16}$ GeV. The model predicts third family top-bottom-tau Yukawa unification, as in minimal SO(10). The other smaller Yukawa couplings are assumed to arise from non-renormalisable operators suppressed by powers of some heavy scale. We perform a systematic operator analysis of the model in order to find the minimum set of operators which describe the low energy quark and lepton masses, and quark mixing angles consistent with low-energy phenomenology. A novel feature of the model is the possibility of asymmetric texture zeroes in the Yukawa matrices at the scale of the new physics. Successful predictions are obtained for $m_t$, $\tan β$, $m_s/m_μ$, $m_d/m_e$ and $V_{ub}$ in terms of a CP violating phase $ϕ$. For example, we predict $\tan β= 35-65$, $m_t = 130 - 190$ GeV, and $|V_{ub}|>0.0040$.

hep-ph↗
arXiv1995

Neutrino Masses and Mixing Angles in a Supersymmetric SU(4)$\otimes$SU(2)$_L\otimes$SU(2)$_R$ Model

We consider the problem of neutrino masses and mixing angles in a supersymmetric model based on the gauge group SU(4)$\otimes$SU(2)$_L\otimes$SU(2)$_R$ broken at the scale $M_X\approx 10^{16}$ GeV. We extend a previous operator analysis of the charged lepton and quark masses and mixing angles in this model to include the neutrino sector, assuming a universal Majorana mass $M$ for the right-handed neutrinos. The Dirac part of the neutrino matrix is then fixed and the physical neutrino masses and magnitudes of all of the elements of the leptonic mixing matrix are then predicted in terms of the single additional parameter $M$. The successful ansatze predict a tau neutrino mass in the relevant range for the dark matter problem and structure formation, muon and electron neutrinos consistent with the MSW solution to the solar neutrino problem, and tau-muon neutrino mixing at a level which should soon be observed by the CHORUS and NOMAD experiments.

hep-ph↗
arXiv1995

Fermion Masses in SUSY GUTs

We discuss the fermion mass problem in SUSY GUTs, including such ideas as texture zeroes, and Georgi-Jarlskog textures. We focus on a specific supersymmetric model based on the gauge group $SU(4)\otimes SU(2)_L \otimes SU(2)_R$. In this model the gauge group is broken to that of the standard model at $10^{16}$ GeV, and supersymmetry is broken at low-energy. The model may be regarded as a ``surrogate SUSY GUT'', and has several advantages over the $SU(5)$ and $SO(10)$ SUSY GUTs, such as the absence of the doublet-triplet splitting problem, and a simpler Higgs sector which does not involve any large Higgs representations. The model predicts full quadruple Yukawa unification (top-bottom-tau-tau neutrino), leading to the prediction of large top mass and $\tan β$. An operator analysis leads to schemes where the strange and down mass are predicted, and $|V_{ub}|>0.004$.

hep-ph↗
arXiv1995

Quadruple Yukawa Unification in the Minimal Supersymmetric Model

Predictions for m_t, tan beta, m_nu_tau are calculated for quadruple third family t-b-tau-nu_tau Yukawa unified models in the MSSM. The renormalisation group equations for the 3 families of the MSSM, including the right handed neutrino, are presented. For right handed tau neutrino Majorana masses that are bigger than 10^11 GeV, the tau neutrino mass is consistent with present cosmological bounds. The m_t, tan beta predictions are approximately equivalent to those in triple third family Yukawa unified models.

hep-ph↗
arXiv1994

Bottom-Tau Yukawa Unification in the Next-to-Minimal Supersymmetric Standard Model

We discuss the unification of the bottom quark and tau lepton Yukawa couplings within the framework of the next-to-minimal supersymmetric standard model. We compare the allowed regions of the $m_t$-$\tan β$ plane to those in the minimal supersymmetric standard model, and find that over much of the parameter space the deviation between the predictions of two models is small, and nearly always much less than the effect of current theoretical and experimental uncertainties in the bottom quark mass and the strong coupling constant. However over some regions of parameter space top-bottom Yukawa unification cannot be achieved. We also discuss the scaling of the light fermion masses and mixing angles, and show that to within current uncertainties the results of recent texture analyses performed for the minimal model also apply to the next-to-minimal model.

hep-ph↗
arXiv1993

Radiative Corrections to Higgs Boson Masses in the Next-to-Minimal Supersymmetric Standard Model

We perform a systematic study of radiative corrections to the masses of the Higgs bosons in the minimal supersymmetric standard model (MSSM) augmented by a single gauge singlet, the so-called next-to-minimal supersymmetric standard model (NMSSM). Our method is based on the one-loop effective potential and includes effects of top quark, squark, Higgs and Higgsino loops. We discuss the renormalisation group flows of Yukawa couplings and the upper bound on the lightest CP-even neutral Higgs boson mass as a function of the heavier stop mass and top mass. We then give a general discussion of Higgs boson phenomenology including radiative corrections. We survey as much of the parameter space of the Higgs sector of the NMSSM as is practicable, and analyse the full spectrum of Higgs masses and couplings in these regions of parameter space. Characteristic signatures of the NMSSM such as light charged bosons and weakly coupled neutral scalars are discussed, as are the relative sizes of the various radiative corrections. The MSSM is also discussed as a limiting case of the NMSSM for comparison.

hep-ph↗
arXiv1993

Squark Contributions to Higgs Boson Masses in the Next--to--Minimal Supersymmetric Standard Model

Within the context of an effective potential formalism we calculate the contribution to Higgs boson masses in the next--to--minimal supersymmetric standard model from squark loops. We then supplement a previously performed renormalisation group analysis of the Higgs sector of this model with these results in order to determine the shift in the bound on the lightest CP-even Higgs boson mass as a result of squark effects. The improved bound on the lightest neutral CP-even Higgs boson mass, including squark contributions, is $m_h \leq 146 \ \ (139, 149)$ GeV for $m_t = 90 \ \ (140, 190)$ GeV. For $m_t = 190$ GeV squark effects contribute 23 GeV to the bound, with smaller contributions for small $m_t$ values.

hep-ph↗
arXiv1993

Supersymmetric Higgs Bosons at the Limit

We obtain an improved upper bound on the lightest neutral CP-even Higgs boson mass from a low energy renormalisation-group analysis of the Higgs sector of the next-to-minimal supersymmetric standard model. We find $m_h< 145$ GeV for $m_t=90$ GeV, decreasing to $m_h< 123$ GeV for $m_t=180$ GeV. We also discuss the light Higgs spectrum in the region of parameter space close to the upper bound.

hep-ph↗
arXiv1992

Heavy Axions From Strong Broken Horizontal Gauge Symmetry

We study the consequences of the existence and breaking of a Peccei--Quinn symmetry within the context of a dynamical model of electroweak symmetry breaking based on broken gauged flavour symmetries. We perform an estimate of the axion mass by including flavour instanton effects and show that, for low cut--offs, the axion is sufficiently massive to prevent it from being phenomenologically unacceptable. We conclude with an examination of the strong CP problem and show that our axion cannot solve the problem, though we indicate ways in which the model can be extended so that the strong CP problem is solved.

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