Robert Foot

A model with fundamental improper spacetime symmetries

Abstract It is shown how the standard model can be extended so that both the lagrangian and the vacuum are invariant under appropriately defined space- and time-inversion transformations. This means that parity and time-reversal may actually be unbroken symmetries of nature.

Lepton masses in an SU ( 3 ) L ⊗ U ( 1 ) N gauge model

The

Comment on ZZ′ mixing in extended gauge theories

SU(3)_c\otimes SU(3)_L\otimes U(1)_N

Possible consequences of parity conservation

model of Pisano and Pleitez extends the Standard Model in a particularly nice way, so that for example the anomalies cancel only when the number of generations is divisible by three. The original version of the model has some problems accounting for the lepton masses. We resolve this problem by modifying the details of the symmetry breaking sector in the model.

Neutrino oscillations and the exact parity model

Abstract In gauge theories with gauge groups containing more than one U (1) gauge group, it is possible to have kinetic mixing terms for the different U (1) gauge fields in the lagrangian. The physical consequences of these mixings are studied. It is shown that electromagnetic interactions are not affected by these mixing terms. The properties of interactioms mediated by massive gauge bosons are modified however. Ways of eliminating the kinetic mixing terms are also discussed.

Electric charge quantization

It has been shown that parity may be an exact unbroken symmetry of nature. This requires a doubling of the number of physical particles, although only two parameters beyond those in the Standard Model are introduced. In this paper, the authors show that the Lagrangian describing parity conserving models can be reformulated in terms of a basis in which each term of the Lagrangian is parity invariant, although gauge invariance is not manifest. The authors then examine some further experimental signatures of parity conservation. The authors point out that, in the simplest case, there is one parity-even and one parity-odd physical neutral Higgs mass eigenstate, whose Yukawa coupling constants are 1/ sq. root 2 that of the Standard Model Higgs boson. Furthermore, half of their widths are generated by almost invisible decay modes. Also, if neutrinos are massive then the ordinary and mirror neutrinos will, in the minimal case, be maximally mixed due to parity conservation. This means that vacuum oscillations can be large, thus providing a possible solution to the solar neutrino problem.

Model for a light Z ’ boson

We re-examine neutrino oscillations in exact parity models. Previously it was shown in a specific model that large neutrino mixing angles result. We show here that this is a general result of neutrino mixing in exact parity models provided that the neutrino mass matrix is real. In this case, the effects of neutrino mixing in exact parity models is such that the probability of a given weak eigenstate remaining in that eigenstate averages to less than half when averaged over many oscillations. This result is interesting in view of the accumulating evidence for a significant deficit in the number of solar neutrinos. It may also be of relevance to the atmospheric neutrino anomaly.

CHARGE QUANTIZATION IN THE STANDARD MODEL AND SOME OF ITS EXTENSIONS

It has been established experimentally for a long time that the electric charges of the observed particles appear to be quantized. An approach to understanding electric-charge quantization that can be used for gauge theories with explicit U(1) factors-such as the standard model and its variants-is pedagogically reviewed and discussed. This approach uses the allowed invariances of the Lagrangian and their associated anomaly cancellation equations. The authors demonstrate that charge may be dequantized in the three-generation standard model with massless neutrinos, because differences in family-lepton numbers are anomaly free. They also review the relevant experimental limits. Their approach too charge quantization suggests that the minimal standard model should be extended so that family-lepton number differences are explicitly broken. They briefly discuss some candidate extensions (e.g. the minimal standard model augmented by Majorana right-handed neutrinos).

Top quark forward-backward asymmetry from SU(

A model of a light [ital Z][prime] boson is constructed and phenomenological bounds are derived. This [ital Z][prime] boson arises from a very simple extension to the standard model, and it is constrained to be light because the vacuum expectation values which generate its mass also break the electroweak gauge group. It is difficult to detect experimentally because it couples exclusively or primarily (depending on symmetry-breaking details) to second and third generation leptons. However, if the [ital Z][prime] boson is sufficiently light, then there exists the possibility of the two-body decay [tau][r arrow][mu][ital Z][prime] occurring. This will provide a striking signature to test the model.

N_c

We review recent advances in the theoretical understanding of electric charge quantization in the Standard Model and some of its extensions. We discuss the roles played by classical constraints, gauge and mixed gauge-gravitational anomaly-cancellation and the demand of vector-like electromagnetic interactions. An attempt is made to clearly explain and contrast the points of view of various authors.