D. J. Smith

Durham University, Durham, ENG, United Kingdom

Are you D. J. Smith?

Claim your profile

Publications (8)16.83 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The fermion masses and mixing angles are fitted using only three free parameters in a nonsupersymmetric extension of the Standard Model, with new, approximately conserved chiral gauge quantum numbers broken by a set of Higgs fields. The fundamental mass scale of this anti-grand-unification model is given by the Planck mass. We also calculate neutrino mixing angles and masses, as well as CP violation from the CKM matrix. A good fit to the observed fermion masses is obtained, but our predictions of the neutrino masses are too small to lead to any observable neutrino oscillation effects claimed today, without introducing another mass scale. We also give some arguments in support of this type of model based on the observed fermion masses.
    International Journal of Modern Physics A 01/2012; 13(29). DOI:10.1142/S0217751X98002353 · 1.09 Impact Factor
  • Source
    CD Froggatt, HB Nielsen, DJ Smith
    [Show abstract] [Hide abstract]
    ABSTRACT: A series of Higgs field quantum numbers in the anti-grand-unification model, based on the gauge group SMG3×U(1)f, is tested against the spectrum of quark and lepton masses and mixing angles. A more precise formulation of the statement that the couplings are assumed of order unity is given. It is found that the corrections coming from this more precise assumption do not contain factors of the order of the number of colors, Nc=3, as one could have feared. We also include a combinatorial correction factor, taking account of the distinct internal orderings within the chain Feynman diagrams in our statistical estimates. Strictly speaking our model predicts that the uncertainty in its predictions and thus the accuracy of our fits should be ±60%. Many of the best fitting quantum numbers give a higher accuracy fit to the masses and mixing angles, although within the expected fluctuations in a χ2. This means that our fit is as good as it can possibly be.
    Physical Review D 05/2002; 65(9). DOI:10.1103/PhysRevD.65.095007 · 4.86 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We describe the Anti-Grand Unification Model (AGUT) and the Multiple Point Principle (MPP) used to calculate the values of the Standard Model gauge coupling constants in the theory, from the requirement of the existence of degenerate vacua. The application of the MPP to the pure Standard Model predicts the existence of a second minimum of the Higgs potential close to the cut-off, which we take to be the Planck scale, giving our Standard Model predictions for the top quark and Higgs masses: $M_t = 173 \pm 5$ GeV and $M_H = 135 \pm 9$ GeV. We also discuss mass protection by chiral charges and present a fit to the charged fermion mass spectrum using the chiral quantum numbers of the maximal AGUT gauge group $SMG^3 \times U(1)_f$, where $SMG \equiv SU(3) \times SU(2) \times U(1)$. The neutrino mass and mixing problem is then briefly discussed for models with chiral flavour charges responsible for the charged fermion mass hierarchy.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The multiple point criticality principle is applied to the pure Standard Model (SM), with a desert up to the Planck scale. We are thereby led to impose the constraint that the effective Higgs potential should have two degenerate minima, one of which should have a vacuum expectation value of order unity in Planck units. In this way we predict a top quark mass of $173 \pm 5$ GeV and a Higgs particle mass of $135 \pm 9$ GeV. The quark and lepton mass matrices are considered in the anti-grand unified extension of the SM based on the gauge group $SMG^3 \otimes U(1)_f$; this group contains three copies of the SM gauge group SMG, one for each generation, and an abelian flavour group $U(1)_f$. The 9 quark and lepton masses and 3 mixing angles are fitted using 3 free parameters, with the overall mass scale set by the electroweak interaction. It is pointed out that the same results can be obtained in an anomaly free $SMG \otimes U(1)^3$ model.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We examine extensions of the standard model (SM), basing our assumptions on what has already been observed; we do not consider anything fundamentally different, such as grand unification or supersymmetry, which is not directly suggested by the SM itself. We concentrate on the possibility of additional low mass fermions (relative to the Planck mass) and search for combinations of representations which do not produce any gauge anomalies. Generalizations of the SM weak hypercharge quantization rule are used to specify the weak hypercharge, modulo 2, for any given representation of the non-Abelian part of the gauge group. Strong experimental constraints are put on our models, by using the renormalization group equations to obtain upper limits on fermion masses and to check that there is no U(1) Landau pole below the Planck scale. Our most promising model contains a fourth generation of quarks without leptons and can soon be tested experimentally.
    Physical Review D 01/1997; 55(3). DOI:10.1103/PhysRevD.55.1592 · 4.86 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the possibility of adding a fourth generation of quarks. We also extend the Standard Model gauge group by adding another SU(N)SU(N) component. In order to cancel the contributions of the fourth generation of quarks to the gauge anomalies we must add a generation of fermions coupling to the SU(N)SU(N) group. This model has many features similar to the Standard Model and, for example, includes a natural generalisation of the Standard Model charge quantisation rule. We discuss the phenomenology of this model and, in particular, show that the infrared quasi-fixed point values of the Yukawa coupling constants put upper limits on the new quark masses close to the present experimental lower bounds.
    Zeitschrift für Physik C 12/1996; 73(2):333-337. DOI:10.1007/s002880050322
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present an extension of the Standard Model (SM) without supersymmetry, which we use to calculate order of magnitude values for the elements of the mass matrices in the SM. In our model we can fit the 9 quark and lepton masses and 3 mixing angles using only 3 free parameters, with the overall mass scale set by the electroweak interaction. The specific model described here has the anti-grand unified gauge group SMG^3 x U(1)_f at high energies where SMG = SU(3) x SU(2) x U(1) is the SM gauge group. The SM fermions are placed in representations of the full gauge group so that they do not produce any anomalies.It is pointed out that the same results can be obtained in an anomaly free SMG x U(1)^3 model. Comment: 15 page LaTeX file, uses FEYNMAN.tex; to be published in Physics Letters B
    Physics Letters B 07/1996; 385(1-4). DOI:10.1016/0370-2693(96)00847-7 · 6.02 Impact Factor