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S. F. King

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

At least 109 records · Page 6Linked to original sources
arXiv2004

Phenomenology of Twisted Moduli in Type I String Inspired Models

We make a first study of the phenomenological implications of twisted moduli in type I intersecting D5-brane models, focussing on the resulting predictions at the LHC using SOFTSUSY to estimate the Higgs and sparticle spectra. Twisted moduli can play an important role in giving a viable string realisation of sequestering in the limit where supersymmetry breaking comes entirely from the twisted moduli. We focus on a particular string inspired version of gaugino mediation in which the first two families are localised at the intersection between D5-branes, whereas the third family and Higgs doublets are allowed to move within the world-volume of one of the branes. The soft supersymmetry breaking third family sfermion mass terms are then in general non-degenerate with the first two families. We place constraints upon parameter space and predictions of flavour changing neutral current effects. Twisted moduli domination is studied and, as well as solving the most serious part of the SUSY flavour problem, is shown to be highly constrained. The constraints are weakened by switching on gravity-mediated contributions from the dilaton and untwisted T-moduli sectors. In the twisted moduli domination limit we predict a stop-heavy MSSM spectrum and quasi-degenerate lightest neutralino and chargino states with wino-dominated mass eigenstates.

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arXiv2004

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

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. We develop the formalism appropriate to electrophobic LIV for Majorana neutrinos, and discuss experimental constraints at current and future neutrino experiments.

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arXiv2004

Best Fit Predictions for Flavour Violating Processes in MSSM Constrained by Unification

We study the Minimal Supersymmetric Standard Model (MSSM) constrained by unification assuming mSUGRA SUSY breaking. In particular this means that the three gauge couplings are unified at a {\it per cent} level, third generation yukawa couplings are unified at a $10 $% level, and at the unification scale $M_U\approx 10^{16}$ the SUSY breaking masses of squarks and sleptons are universal up to specific D-term contributions. At $M_U$ we also include right-handed neutrinos that are decoupled at their three respective scales. In a top-down global analysis we then find that there are two distinct best fits, primarily distinguished by the masses of the non-Standard Model Higgs states, and compute the predictions for flavour violating processes involving both leptons and quarks. The fit with the light Higgs spectrum is especially interesting with regards to the decay $B_s\to μ^+μ^-$. We note that the latter results go beyond what is called minimal flavour violation in the MSSM.

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arXiv2003

The Soft Supersymmetry-Breaking Lagrangian: Theory and Applications

After an introduction recalling the theoretical motivation for low energy (100 GeV to TeV scale) supersymmetry, this review describes the theory and experimental implications of the soft supersymmetry-breaking Lagrangian of the general minimal supersymmetric standard model (MSSM). Extensions to include neutrino masses and nonminimal theories are also discussed. Topics covered include models of supersymmetry breaking, phenomenological constraints from electroweak symmetry breaking, flavor/CP violation, collider searches, and cosmological constraints including dark matter and implications for baryogenesis and inflation.

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arXiv2003

Neutrino Mass Models

This is a review article about neutrino mass models, particularly see-saw models involving three active neutrinos which are capable of describing both the atmospheric neutrino oscillation data, and the large mixing angle MSW solar solution, which is now uniquely specified by recent data. We briefly review the current experimental status, show how to parametrise and construct the neutrino mixing matrix, and present the leading order neutrino Majorana mass matrices. We then introduce the see-saw mechanism, and discuss a natural application of it to current data using the sequential dominance mechanism, which we compare to an early proposal for obtaining large mixing angles. We show how both the Standard Model and the Minimal Supersymmetric Standard Model may be extended to incorporate the see-saw mechanism, and show how the latter case leads to the expectation of lepton flavour violation. The see-saw mechanism motivates models with additional symmetries such as unification and family symmetry models, and we tabulate some possible models, before focussing on two particular examples based on SO(10) grand unification and either U(1) or SU(3) family symmetry as specific examples. The article contains extensive appendices which include techniques for analytically diagonalising different types of mass matrices involving two large mixing angles and one small mixing angle, to leading order in the small mixing angle.

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arXiv2003

Preheating curvature perturbations with a coupled curvaton

We discuss the potentially important role played by preheating in certain variants of the curvaton mechanism in which isocurvature perturbations of a D-flat (and F-flat) direction become converted to curvature perturbations during reheating. We analyse the transition from inflation to reheating in some detail, including the dynamics of the coupled curvaton and inflation fields during this transition. We discover that preheating could be an important source of adiabaticity where parametric resonance of the isocurvature components amplifies the super-horizon fluctuations by a significant amount. As an example of these effects we develop a particle physics motivated model which we recently introduced in which the D-flat direction is identified with the usual Higgs field. Our new results show that it is possible to achieve the correct curvature perturbations for initial values of the curvaton fields of order the weak scale. In this model we show that the prediction for the spectral index of the final curvature perturbation only depends on the mass of the curvaton during inflation, where consistency with current observational data requires the ratio of this mass to the Hubble constant to be < 0.3.

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arXiv2003

The flavour problem and family symmetry

We show how two different family symmetries can be used to address the flavour problem in SO(10)-like models. The first is based on a gauged $U(1)_F$, whose problems dissappear in the context of a type I string model embedding. The second is based on $SU(3)_F$, the maximal family group consistent with SO(10); in this case the family symmetry is more constaining, so we merely look at it in the context of a supersymmetric field theory

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arXiv2003

Fermion Masses and Mixing Angles from SU(3) Family Symmetry and Unification

We develop a bottom-up approach to constructing a theory of fermion masses and mixing angles based on the gauge group $SU(3)\times G$ where SU(3) is a family symmetry and $G$ contains a unified group such as SO(10) or its Pati-Salam subgroup, together with other discrete symmetries. We construct a realistic model and show that it can provide an excellent description of quark and lepton masses and mixing angles, including almost maximal atmospheric mixing and the LMA MSW solar neutrino solution. We predict a neutrino mixing angle $θ_{13}$ near the current limit. The model provides the basis for a new solution to the flavour problem with a characteristic soft SUSY breaking mass spectrum.

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arXiv2003

Implications of $B_s\to μ^{+}μ^{-}$ in SO(10)-like Models

We examine the potentially very promising signal $B_s\to μ^{+}μ^{-}$ in supersymmetry with large $\tanβ$ in a {\em top-down} approach starting from the best fits of an SO(10)-like model studied recently. Our results go beyond minimal flavour violation investigated in previous works. We show that the absolute best fits provide a signal for $B_s\to μ^{+}μ^{-}$ at the borderline of the present limits and hence the ongoing search at the Tevatron will start having an impact on the global analysis of this class of SUSY models. We discuss the implications of a measurement of $B_s\to μ^{+}μ^{-}$ for restricting the parameter space of gauginos and sfermion masses, and of signals in other channels $B_{d,s}\to l^{+}+l^{-}$. We also discuss correlations of $B_s\to μ^{+}μ^{-}$ with the CP-odd Higgs mass, $\sin (β-α)$ and $b\to s γ$ in SO(10)-like models.

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arXiv2003

Neutrino Mass, Flavour and CP Violation

In this talk I discuss the connection between neutrino mass, flavour and CP violation. I focus on three neutrino patterns of neutrino masses and mixing angles, and the corresponding Majorana mass matrices. I discuss the see-saw mechanism, and show how it may be applied in a very natural way to give a neutrino mass hierarchy with large atmospheric and solar angles by assuming sequential right-handed neutrino dominance. I then distinguish between heavy sequential dominance and light sequential dominance, and show how lepton flavour violation in the CMSSM provides a way to discriminate between these two possibilities. I also show that for a well motivated class of light sequential dominance models there is a link between leptogenesis and CP violation measurable in neutrino oscillation experiments.

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arXiv2003

Leptogenesis-MNS Link in Unified Models with Natural Neutrino Mass Hierarchy

We discuss the relation between leptogenesis and the MNS phases in the class of see-saw models called light sequential dominance in which the right-handed neutrinos dominate sequentially, with the dominant right-handed neutrino being the lightest one. The heaviest right-handed neutrino then decouples, leaving effectively two right-handed neutrinos. Light sequential dominance is motivated by SO(10) models which predict three right-handed neutrinos. With an approximate Yukawa texture zero in the 11 position there are only two see-saw phases which are simply related to the MNS phase measurable at a neutrino factory and the leptogenesis phase. The leptogenesis phase is predicted to be equal to the neutrinoless double beta decay phase.

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arXiv2003

Inflation, Large Scale Structure and Particle Physics

We review experimental and theoretical developments in inflation and its application to structure formation, including the curvaton idea. We then discuss a particle physics model of supersymmetric hybrid inflation at the intermediate scale in which the Higgs scalar field is responsible for large scale structure, and show how such a theory is completely natural in the framework extra dimensions with an intermediate string scale.

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arXiv2003

Lepton Flavour Violation in the Constrained MSSM with Natural Neutrino Mass Hierarchy

We present predictions for $μ\to e γ$ and $τ\to μγ$ in the CMSSM in which there is a natural hierarchy of neutrino masses resulting from the sequential dominance of three right-handed neutrinos. We perform a global analysis of this model in the $(m_0,M_{1/2})$ plane, assuming radiative electroweak symmetry breaking, and including all observed laboratory data. We confirm that a large (small) $τ\to μγ$ rate results from the dominant right-handed neutrino being the heaviest (lightest) one. We show that the $μ\to e γ$ rate may determine the order of the sub-dominant neutrino Yukawa couplings in the flavour basis, but may also be sensitive to effects beyond the leading log and leading mass insertion approximations. We also show that the $μ\to e γ$ rate is independent of $θ_{13}$, but measurement of this angle may determine a ratio of sub-dominant Yukawa couplings.

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arXiv2003

Global Analysis of a Supersymmetric Pati-Salam Model

We perform a complete global phenomenological analysis of a realistic string-inspired model based on the supersymmetric Pati-Salam $SU(4)\times SU(2)_L \times SU(2)_R$ gauge group supplemented by a U(1) family symmetry, and present predictions for all observables including muon $g-2$, $τ\to μγ$, and the CHOOZ angle. Our analysis demonstrates the compatibility of such a model with all laboratory data including charged fermion masses and mixing angles, LMA MSW and atmospheric neutrino masses and mixing angles, and $b \to s γ$, allowing for small deviations from third family Yukawa unification. We show that in such models the squark and slepton masses may be rather light compared to similar models with exact Yukawa unification.

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arXiv2003

A Supersymmetric Standard Model of Inflation with Extra Dimensions

We embed the supersymmetric standard model of hybrid inflation based on the next-to-minimal superpotential term $λNH_uH_d$ supplemented by an inflaton term $κϕN^2$, into an extra-dimensional framework, in which all the Higgs fields and singlets live in the bulk, while all the matter fields live on the brane. All the parameters of the effective 4d model can then be naturally understood in terms of a fundamental (``string'') scale $M_*\sim 10^{13}$ GeV and a brane supersymmetry breaking scale $10^{8}$ GeV, of the same order as the height of the inflaton potential during inflation. In particular the very small Yukawa couplings $λ\sim κ\sim 10^{-10}$ necessary for the model to solve the strong CP problem and generate the correct effective $μ$ term after inflation, can be naturally understood in terms of volume suppression factors. The brane scalar masses are naturally of order a TeV while the bulk inflaton mass is naturally in the MeV range sufficient to satisfy the slow roll constraints. Curvature perturbations are generated after inflation from the isocurvature perturbations of the supersymmetric Higgs as discussed in a companion paper.

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arXiv2003

Large Scale Structure from the Higgs fields of the Supersymmetric Standard Model

We propose an alternative implementation of the curvaton mechanism for generating the curvature perturbations which does not rely on a late decaying scalar decoupled from inflation dynamics. In our mechanism the supersymmetric Higgs scalars are coupled to the inflaton in a hybrid inflation model, and this allows the conversion of the isocurvature perturbations of the Higgs fields to the observed curvature perturbations responsible for large scale structure to take place during reheating. We discuss an explicit model which realises this mechanism in which the $μ$ term in the Higgs superpotential is generated after inflation by the vacuum expectation value of a singlet field. The main prediction of the model is that the spectral index should deviate significantly from unity, $|n-1|\sim 0.1$. We also expect relic isocurvature perturbations in neutralinos and baryons, but no significant departures from gaussianity and no observable effects of gravity waves in the CMB spectrum.

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arXiv2003

Gamma ray bursts as probes of neutrino mass, quantum gravity and dark energy

We calculate the time delays of neutrinos emitted in gamma ray bursts due to the effects of neutrino mass and quantum gravity using a time dependent Hubble constant which can significantly change the naive results presented hitherto in the literature for large redshifts, and gives some sensitivity to the details of dark energy. We show that the effects of neutrino mass, quantum gravity and dark energy may be disentangled by using low energy neutrinos to study neutrino mass, high energy neutrinos to study quantum gravity, and large redshifts to study dark energy. From low energy neutrinos one may obtain direct limits on neutrino masses of order 10^{-3} eV, and distinguish a neutrino mass hierarchy from an inverted mass hierarchy. From ultra-high energy neutrinos the sensitivity to the scale of quantum gravity can be pushed up to E_{QG} ~ 5 times 10^{30} GeV. By studying neutrinos from GRBs at large redshifts a cosmological constant could be distinguished from quintessence.

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