arXiv subjects

Steve F. King

Publications and source records attributed to Steve F. King.

29 records · Page 2Linked to original sources

arXiv2004

Type II Leptogenesis and the Neutrino Mass Scale

We discuss the effect of the neutrino mass scale on baryogenesis via the out-of-equilibrium decay of the lightest right-handed (s)neutrinos in type II see-saw models. We calculate the type II contributions to the decay asymmetries for minimal scenarios based on the Standard Model and on the Minimal Supersymmetric Standard Model, where the additional direct mass term for the neutrinos arises from a Higgs triplet vacuum expectation value. The result in the supersymmetric case is new and we correct the previous result in the scenario based on the Standard Model. We confirm and generalize our results by calculating the decay asymmetries in an effective approach, which is independent of the realization of the type II contribution. We derive a general upper bound on the decay asymmetry in type II see-saw models and find that it increases with the neutrino mass scale, in sharp contrast to the type I case which leads to an upper bound of about 0.1 eV on the neutrino mass scale. We find a lower bound on the mass of the lightest right-handed neutrino, significantly below the corresponding type I bound for partially degenerate neutrinos. This lower bound decreases with increasing neutrino mass scale, making leptogenesis more consistent with the gravitino constraints in supersymmetric models.

hep-ph↗

arXiv2004

Neutrino Mixing from the Charged Lepton Sector with Sequential Right-Handed Lepton Dominance

We systematically analyze the possibility that bi-large lepton mixing originates from the charged lepton sector in models with sequential dominance for the right-handed charged leptons. We derive analytical expressions for the mixing angles and CP phases of the MNS matrix for the case of zero mixing from the neutrino sector, which is arranged for with the help of sequential dominance for the right-handed neutrinos. For small $θ_{13}$, the two large mixing angles $θ_{12}$ and $θ_{23}$ are determined by the Yukawa couplings to the dominant right-handed tau. The mixing angle $θ_{13}$ is then governed by the subdominant right-handed muon Yukawa couplings. Naturally small $θ_{13}$ and sequential right-handed lepton dominance can be realized in type I see-saw models and their type II upgrades via spontaneously broken SO(3) flavour symmetry and real vacuum alignment. We discuss the prediction for $θ_{13}$ in this scenario and corrections to it including the dependence on the neutrino mass scale.

hep-ph↗

arXiv2004

Canonical normalisation and Yukawa matrices

We highlight the important role that canonical normalisation of kinetic terms in flavour models based on family symmetries can play in determining the Yukawa matrices. Even though the kinetic terms may be correctly canonically normalised to begin with, they will inevitably be driven into a non-canonical form by a similar operator expansion to that which determines the Yukawa operators. Therefore in models based on family symmetry canonical re-normalisation is mandatory before the physical Yukawa matrices can be extracted. In nearly all examples in the literature this is not done. As an example we perform an explicit calculation of such mixing associated with canonical normalisation of the Kahler metric in a supersymmetric model based on SU(3) family symmetry, where we show that such effects can significantly change the form of the Yukawa matrix. In principle quark mixing could originate entirely from canonical normalisation, with only diagonal Yukawa couplings before canonical normalisation.

hep-ph↗

arXiv2003

Neutrino Physics and the flavour problem

We consider the problem of trying to understand the recently measured neutrino data simultaneously with understanding the heirarchical form of quark and charged lepton Yukawa matrices. We summarise the data that a sucessful model of neutrino mass must predict, and then move on to attempting to do so in the context of spontaneously broken `family' symmetries. We consider first an abelian U(1) family symmetry, which appears in the context of a type I string model. Then we consider a model based on a non-abelian SU(3)_F, which is the maximal family group consitent with an SO(10) GUT. In this case the symmetry is more constraining, and is examined in the context of SUSY field theory.

hep-ph↗

arXiv2003

Lepton Flavour Violation from Yukawa Operators, Supergravity and the See-Saw mechanism

We investigate the phenomenological impact of different sources of lepton flavour violation arising from realistic models based on supergravity mediated supersymmetry breaking with Yukawa operators. We discuss four distinct sources of lepton flavour violation in such models: minimum flavour violation, arising from neutrino masses and the see-saw mechanism with RG running; supergravity flavour violation due to the non-universal structure of the supergravity model; flavour violation due to Froggatt-Nielsen (FN) fields appearing in Yukawa operators developing supersymmetry breaking F-terms and contributing in a non-universal way to soft trilinear terms; and finally heavy Higgs flavour violation arising from the heavy Higgs fields used to break the unified gauge symmetry which also appear in Yukawa operators and behave analagously to the FN fields. In order to quantify the relative effects, we study a particular type I string inspired model based on a supersymmetric Pati-Salam model arising from intersecting D-branes, supplemented by a U(1) family symmetry

hep-ph↗

arXiv2003

Summary of Working Group 2

Issues on the physics of, beamlines for, and detectors of neutrino oscillation discussed in Working Group 2 at Nufact'02 are summarized.

hep-ph↗

arXiv2000

Radiative Corrections to Chargino Production with Polarized Beams

We show that radiative corrections to chargino production in electron-positron annihilation with polarized beams can be large especially in the case of right handed electrons. In addition, there is some dependency on the squark masses that allows us to extract information about the squark spectrum from the chargino production.

hep-ph↗

arXiv1998

Radiatively Corrected Chargino Pair Production at LEP2

One-loop radiative corrections to the production cross section of a pair of light charginos in e+e- colliders are calculated within the MSSM. Top and bottom quarks and squarks are considered in the loops, and they are renormalized using the MS-bar scheme. If the center of mass energy is equal to 192 GeV, positive corrections typically of 10% to 15% are found when the squark mass parameters are equal to 1 TeV.

hep-ph↗

arXiv1997

Radiative Corrections to Chargino Production in Electron-Positron Collisions

We discuss the one-loop radiative corrections to the reaction e^+ e^- -> X^+_a X^-_b, for a,b=1,2 where X^+_{1,2} are the charginos of the minimal supersymmetric standard model. We calculate the leading one loop radiative corrections involving loops of top, stop, bottom and sbottom quarks, working in the MS-bar scheme. At LEP2 we find positive radiative corrections typically of 10% to 15% and with a maximum value of approximately 30% if the squark mass parameters are of the order of 1 TeV. If \sqrt{s}=500 GeV we find smaller corrections but they can be also negative, with extreme values of 13% and -4%. For a center of mass given by \sqrt{s}=2 TeV we find larger corrections, with typical values between 20% and -20%.

hep-ph↗

arXiv1996

Chargino Production at LEP2 in a Supergravity Model

In the framework of a particular supergravity model which provides a natural solution to the $μ$--problem we show how the discovery of a chargino at LEP2 and the measurement of its mass and production cross--section, together with the measurement of the mass of the lightest neutralino, would determine the entire Higgs and SUSY spectrum. We give detailed predictions for the Higgs and SUSY spectrum as a function of the chargino production cross--section, for constant values of the lightest chargino and gluino masses.

hep-ph↗

arXiv1995

Charginos and Neutralinos at LEPII

We show that LEPII will either discover charginos and neutralinos, or enable a very stringent upper limit to be placed on $\tan β$ as a function of the gluino mass. The only assumption we make is the existence of some unified model which breaks down to the minimal supersymmetric standard model below the unification scale. In such a framework we discuss how the discovery of a chargino at LEPII and the measurement of its mass and production cross-section, together with the measurement of the mass of the lightest neutralino, would enable the gluino mass, $\tan β$ and $μ$ to be predicted, up to a possible ambiguity in the sign of $μ$ which we discuss.

hep-ph↗