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S. F. King

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

At least 145 records · Page 8Linked to original sources
arXiv2001

Brane Mediated Supersymmetry Breaking

We propose a mechanism for mediating supersymmetry breaking in Type I string constructions. The basic set-up consists of a system of three D-branes: two parallel D-branes, a matter D-brane and a source D-brane, with supersymmetry breaking communicated via a third D-brane, the mediating D-brane, which intersects both of the parallel D-branes. We discuss an example in which the first and second family matter fields correspond to open strings living on the intersection of the matter D-brane and mediating D-brane, while the gauge fields, Higgs doublets and third family matter fields correspond to open strings living on the mediating D-brane. As in gaugino mediated models, the gauginos and Higgs doublets receive direct soft masses from the source brane, and flavour-changing neutral currents are naturally suppressed since the first and second family squarks and sleptons receive suppressed soft masses. However, unlike the gaugino mediated model, the third family squarks and sleptons receive unsuppressed soft masses, resulting in a very distinctive spectrum with heavier stops, sbottoms and staus.

hep-ph↗
arXiv2000

Leptogenesis in a Realistic Supersymmetric Model of Inflation with a Low Reheat Temperature

We discuss leptogenesis in a realistic supersymmetric model of inflation with a low reheat temperature 1-10 GeV. The lepton asymmetry is generated by a decaying right handed sneutrino, which is produced after inflation during preheating. The inflationary model is based on a simple variant of the Next-to-Minimal Supersymmetric Standard model (NMSSM) which solves the μproblem, called \phiNMSSM, where the additional singlet ϕplays the role of the inflaton in hybrid (or inverted hybrid) type models. The model is invariant under an approximate Peccei-Quinn symmetry which also solves the strong CP problem, and leads to an invisible axion with interesting cosmological consequences. We show how the baryon number of the universe and the nature of cold dark matter are determined by the same parameters controlling the strong CP problem, the μproblem and the neutrino masses and mixing angles.

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arXiv2000

Neutrino Masses in SUSY Models

In this talk we assume the conventional see-saw mechanism, and contruct a hierarchical pattern of three active neutrinos with bi-maximal mixing. In order to enforce the hierarchy we use the single right handed neutrino dominance mechanism which is a very nice way to ensure a neutrino mass hierarchy in the presence of large mixing angles. We show how this mechanism can be organised in the framework of a U(1) family symmetry, then discuss a realistic string-inspired model which includes such a symmetry.

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arXiv2000

What Will We Learn If a Higgs Boson is Found?

We examine what can be deduced from the discovery of a Higgs boson, focusing on a possible discovery at LEP. The analysis begins with the most general situation where no further constraints can be deduced, and then specializes to include various assumptions. Assuming naturalness, the relatively large mass suggests that one or more of larger $\tan β$, large phase, or extra singlets is present. We discuss the implications of a Higgs mass discovery for the SUSY spectrum, and in particular gluinos and stops. We show that a lighter gluino produceable at the Tevatron remains a likely possibility, in disagreement with a recent claim.

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arXiv2000

Neutrino Masses and Mixing Angles in a Realistic String-Inspired Model

We analyse a supersymmetric string-inspired model of all fermion masses and mixing angles based on the Pati-Salam $SU(4)\times SU(2)_L \times SU(2)_R$ gauge group supplemented by a $U(1)_X$ flavour symmetry. The model involves third family Yukawa unification and predicts the top mass and the ratio of the vacuum expectation values $\tan β$. The model also provides a successful description of the CKM matrix and predicts the masses of the down and strange quarks. However our main focus is on the neutrino masses and MNS mixing angles, and we show how the recent atmospheric neutrino mixing observed by Super-Kamiokande, and the MSW solution to the solar neutrino problem lead to important information about the flavour structure of the model near the string scale. We show how single right-handed neutrino dominance may be implemented by the use of ``Clebsch zeros'', leading to the LMA MSW solution, corresponding to bi-maximal mixing. The LOW MSW and SMA MSW solutions are also discussed.

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arXiv2000

Renormalisation Group Analysis of Single Right-handed Neutrino Dominance

We perform a renormalisation group (RG) analysis of neutrino masses and mixing angles in the see-saw mechanism in the minimal supersymmetric standard model with three right-handed neutrinos, including the effects of the heavy neutrino thresholds. We focus on the case that one of the right-handed neutrinos provides the dominant contribution to the 23 block of the light Majorana matrix, causing its determinant to approximately vanish and giving an automatic neutrino mass hierarchy, so called single right-handed neutrino dominance which may arise from a U(1) family symmetry. In these models radiative corrections can increase atomospheric and solar neutrino mixing by up to about 10% and 5%, respectively, and may help to achieve bi-maximal mixing. Significantly we find that the radiative corrections over the heavy neutrino threshold region are at least as important as those usually considered from the lightest right-handed neutrino down to low energies.

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arXiv2000

Yukawa Unification as a Window into the Soft Supersymmetry Breaking Lagrangian

We study Yukawa unification, including the effects of a physical neutrino mass consistent with the Superkamiokande observations, in a string/$D$-brane inspired Pati-Salam model which allows the most general non-universal scalar and gaugino masses, including the usual $D$-term contributions which arise in SO(10). We investigate how the tight constraints from rare decays such as $b \to s γ$ and $τ\to μγ$ can provide information about the family dependent supersymmetry breaking soft Lagrangian, for example the trilinears associated with the second and third family. Many of our results also apply to SO(10) to which the model approximately reduces in a limiting case. In both models we find that Yukawa unification is perfectly viable providing the non-universal soft masses have particular patterns. In this sense Yukawa unification acts as a window into the soft supersymmetry breaking Lagrangian.

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arXiv2000

Inverted Hierarchy Models of Neutrino Masses

We study models of neutrino masses which naturally give rise to an inverted mass hierarchy and bi-maximal mixing. The models are based on the see-saw mechanism with three right-handed neutrinos, which generates a single mass term of the form $ν_e(ν_μ+ν_τ)$ corresponding to two degenerate neutrinos $ν_e$ and $ν_μ+ν_τ$, and one massless neutrino $ν_μ-ν_τ$. Atmospheric neutrino oscillations are accounted for if the degenerate mass term is about $5\times 10^{-2}$ eV. Solar neutrino oscillations of the Large Mixing Angle MSW type arise when small perturbations are included leading to a mass splitting between the degenerate pair of about $(1.7-2.0)\times 10^{-4}$ eV for the successful cases. We study the conditions that such models must satisfy in the framework of a U(1) family symmetry broken by vector singlets, and catalogue the simplest examples. We then perform a renormalisation group analysis of the neutrino masses and mixing angles, assuming the supersymmetric standard model, and find modest radiative corrections of a few per cent, showing that the model is stable. At low energies we find $\sin^22θ_{23}\approx 0.93-0.96$ and $\sin^22θ_{12}\approx 0.9-1.0$.

hep-ph↗
arXiv2000

Does LEP prefer the NMSSM?

We study the naturalness of electroweak symmetry breaking and baryogenesis in the next-to-minimal supersymmetric standard model (NMSSM). Our study is motivated by the recent LEP bounds on the Higgs boson mass which severely constrains the low \tanβregion of the minimal supersymmetric standard model (MSSM). We show that the low \tan βregion of the NMSSM is clearly favoured over the MSSM with regard to the physical Higgs boson mass, fine-tuning, and electroweak baryogenesis.

hep-ph↗
arXiv2000

D Branes and Textures

We examine the flavor structure of the trilinear superpotential couplings which can result from embedding the Standard Model within D brane sectors in Type IIB orientifold models, which are examples within the Type I string framework. We find in general that the allowed flavor structures of the Yukawa coupling matrices to leading order are given by basic variations on the "democratic" texture ansatz. In certain interesting cases, the Yukawa couplings have a novel structure in which a single right-handed fermion couples democratically at leading order to three left-handed fermions. We discuss the viability of such a ``single right-handed democracy'' in detail; remarkably, even though there are large mixing angles in the u,d sectors separately, the CKM mixing angles are small. The analysis demonstrates the ways in which the Type I superstring framework can provide a rich setting for investigating novel resolutions to the flavor puzzle.

hep-ph↗
arXiv2000

Large Mixing Angle MSW and Atmospheric Neutrinos from Single Right-Handed Neutrino Dominance and U(1) Family Symmetry

Single right-handed neutrino dominance (SRHND) in the 23 sector of the light effective neutrino mass matrix has been proposed as a natural explanation for the concurrent large 23 mixing angle and large 23 mass hierarchy. In this paper we show how large 12 mixing angles, suitable for the large mixing angle (LMA) MSW solution to the solar neutrino problem, may arise from SRHND. In order to understand the conditions for SRHND and LMA MSW we first consider the case of one and two right-handed neutrinos, and obtain simple analytic conditions which are then extended to the case of three right-handed neutrinos. We then introduce a single U(1) family symmetry and show how these analytic conditions may be translated into U(1) charge assignments and perform a systematic search for the simplest examples.

hep-ph↗
arXiv2000

Report of the Beyond the Standard Model Working Group of the 1999 UK Phenomenology Workshop on Collider Physics (Durham)

The Beyond the Standard Model Working Group discussed a variety of topics relating to exotic searches at current and future colliders, and the phenomenology of current models beyond the Standard Model. For example, various supersymmetric (SUSY) and extra dimensions search possibilities and constraints are presented. Fine-tuning implications of SUSY searches are derived. The implications of Higgs (non)-discovery are discussed, as well as the program HDECAY. The individual contributions are included seperately. Much of the enclosed work is original, although some is reviewed.

hep-ph↗
arXiv2000

Can Flavor-Independent Supersymmetry Soft Phases Be the Source of All CP Violation?

Recently it has been demonstrated that large phases in softly broken supersymmetric theories are consistent with electric dipole moment constraints, and are motivated in some (Type I) string models. Here we consider whether large flavor-independent soft phases may be the dominant (or only) source of all CP violation. In this framework $ε$ and $ε'/ε$ can be accommodated, and the SUSY contribution to the B system mixing can be large and dominant. An unconventional flavor structure of the squark mass matrices (with enhanced super-CKM mixing) is required for consistency with B and K system observables.

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arXiv1999

Fine-Tuning Constraints on Supergravity Models

We discuss fine-tuning constraints on supergravity models. The tightest constraints come from the experimental mass limits on two key particles: the lightest CP even Higgs boson and the gluino. We also include the lightest chargino which is relevant when universal gaugino masses are assumed. For each of these particles we show how fine-tuning increases with the experimental mass limit, for four types of supergravity model: minimal supergravity, no-scale supergravity (relaxing the universal gaugino mass assumption), D-brane models and anomaly mediated supersymmetry breaking models. Among these models, the D-brane model is less fine tuned.The experimental propects for an early discovery of Higgs and supersymmetry at LEP and the Tevatron are discussed in this framework.

hep-ph↗
arXiv1999

Atmospheric and Solar Neutrinos from Single Right-Handed Neutrino Dominance and U(1) Family Symmetry

We argue that in order to provide a natural explanation of both neutrino mass hierarchies and large neutrino mixing angles, as required by the atmospheric neutrino data, a single right-handed neutrino must give the dominant contribution to the 23 block of the light effective neutrino matrix, and illustrate this mechanism in the framework of models with U(1) family symmetries. Sub-dominant contributions from other right-handed neutrinos are required to give small mass splittings appropriate to the small angle MSW solution to the solar neutrino problem. We give general conditions for achieving this in the framework of U(1) family symmetry models containing arbitrary numbers of right-handed neutrinos, and show how the resulting neutrino mass hierarchies and mixing angles may be expanded in terms of the Wolfenstein parameter.

hep-ph↗
arXiv1999

Large or Small Angle MSW from Single Right-Handed Neutrino Dominance

In this talk we discuss a natural explanation of both neutrino mass hierarchies {\it and} large neutrino mixing angles, as required by the atmospheric neutrino data, in terms of a single right-handed neutrino giving the dominant contribution to the 23 block of the light effective neutrino matrix, and illustrate this mechanism in the framework of models with U(1) family symmetries. Sub-dominant contributions from other right-handed neutrinos are required to give small mass splittings appropriate to the MSW solution to the solar neutrino problem. We present three explicit examples for achieving the small angle MSW solution in the framework of U(1) family symmetry models containing three right-handed neutrinos, which can naturally describe all quark and lepton masses and mixing angles. In this talk we also extend the analysis to the large angle MSW solution.

hep-ph↗
arXiv1999

Preheating in Supersymmetric Hybrid Inflation

We study preheating in a general class of supersymmetric hybrid inflation model. Supersymmetry leads to only one coupling constant in the potential and thus only one natural frequency of oscillation for the homogeneous fields, whose classical evolution consequently differs from that of a general (non-supersymmetric) hybrid model. We emphasise the importance of mixing effects in these models which can significantly change the rate of production of particles. We perform a general study of the rate of production of the particles associated with the homogeneous fields, and show how preheating is efficient in producing these quanta. Preheating of other particle species will be model dependent, and in order to investigate this we consider a realistic working model of supersymmetric hybrid inflation which solves the strong-CP problem via an approximate Peccei-Quinn symmetry, which was proposed by us previously. We study axion production in this model and show that properly taking into account the mixing between the fields suppresses the axion production, yet enhances the production of other particles. Finally we demonstrate the importance of backreaction effects in this model which have the effect of shutting off axion production, leaving the axion safely within experimental bounds.

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