High-colour and mass hierarchies

We present a model based on the gauge group G = G_HC × G_S × SU(2)_L × U(1), where the hypercolour gauge group G_HC is responsible for the dynamical breaking of the strong group G_S to SU(3)_C of QCD. Chiral symmetry breaking of high-colour representations produces dynamical breaking of the electroweak SU(2)_L × U(1) gauge group. Fermion masses and flavour mixing are dynamically generated from the condensations of high-colour representations. A phenomenological analysis of the model is also presented.     

Radiative corrections to quark-lepton mass matrices in superstring-inspired models

We examine if quark-lepton mass matrices are modified by generation changing currents in superstring-inspired models. It is shown that sufficiently large corrections to the quark mass matrices can be derived in an SU(3)_C × SU(2)_L × SU(2)_R × U(1)_L × U(1)_R model with δ ⩾ 2 and an SU(3)_C × SU(2)_L × U(1)_L × U(1)_R model. Consistency with other experiments are investigated by means of renormalization group equations.     

Chiral symmetry breaking and condensates in the rishon model

The rishon model is studied in the limit g_c → 0, α → 0 when its global flavour symmetry is SU(6) × SU(6) × U(1) analogous to six massless flavour QCD. Recently it was shown that the ad hoc breaking SU(6) × SU(6) → SU(3) × SU(3) allows the anomaly constraint to be satisfied. In this paper this is shown to be but one of several successful patterns of chiral symmetry breaking. The condensates required to perform these breakings are fully discussed. A plausibility argument based on single gauge boson exchange is presented which determines the condensate uniquely to be 〈(v_LV_L)³〉 corresponding to the original breaking above. The same argument applies to QCD, which is argued to differ in its chiral behaviour due to the large intrinsic masses of the quarks. The implications of the above condensate and pattern of chiral symmetry breaking for the rishon model include the prediction of integer charged colour octet fermions, a naive mass formula m_e = 2m_u ? m_d, new insight into the parity-violating condensate 〈(v_Lv_L)²(v_Rv_R)〉 and the prediction of 52 new pseudos whose masses are estimated.     

Prospects for supersymmetric SO(10) models with an intermediate mass scale

We investigate possible patterns of SO(10) gauge symmetry breaking compatible with supersymmetry, limiting ourselves to the cases with one intermediate breaking scale. It is found that the one where a 54 representation breaks SO(10) into a Pati-Salam group SU(4)_C×SU(2)_L×SU(2)_R and the one where a 210 breaks it into SU(3)_C× U(1)_C×SU(2)_L×SU(2)_R are the most preferable patterns when supersymmetry is taken into account. Two models with the Pati-Salam intermediate symmetry are studied in more detail.     

Grand unified model with a stable proton and no axion problem

We present a grand unified model of the strong, electromagnetic and weak interactions based on a local SU(8)_L×SU(8)_R gauge theory which possesses a global U(8)_L × U(8)_R invariance. We break the symmetry down to the standard SU(3)_C × SU(2)_L × U(1) model, with the proton remaining stable and the left-handed neutrinos obliged to remain massless. A novel feature of our model is the simultaneous absence of both strong CP violations and of axions.     

Parity violation in atoms within left-right symmetric gauge models

Predictions for parity violation in atoms within left-right symmetric theories based on the gauge groups SU(2)_L × SU(2)_R × U(1) and SU(2)_L × SU(2)_L × SU(2)_R × U(1)_L × U(1)_R are presented.     

Parity violations in electron-nucleon scattering and the SU(2)L ×SU(2)R ×U(1)L+R electroweak symmetry

The SU(2)_L ×SU(2)_R ×U(1)_L+R model of elecroweak interactions is described with the most general gauge couplings g_L, g_Randg_L+R. The case in which neutrino neutral current interactions are identical to the standard SU(2)_L ×U(1)_L+R model is discussed in detail. It is shown that with the weak angle lying in the experimental range sin²θ_w = 0.23 ± 0.015 and 1 < g_L²/g_R² < 3 it is possible to explain the amount of parity violation observed at SLAC and at the same time predict values of the “weak charge” in bismuth to lie in the range admitted by the controversal data from different experiments.     

Limits on the top quark mass within the frame of the minimal superstrings inspired model

We study the process of spontaneous R parity breaking in minimal stringy models. In these models the top quark mass is bounded from below to allow the spontaneous breaking of SU (2)_L × U (1)_Y. On the other hand the requirement of stability for the neutral potential which is sufficient to avoid R parity breaking, gives us an upper bound. Allowed values for the top quark mass remain between 70 and 95 GeV, if supersymmetry breaking is triggered by gaugino masses.     

A supersymmetric left-right confining model of the weak interactions

We extend the supersymmetric, confining theory of weak interactions to a left-right symmetric model. This model is based on the gauge group SU(M)_SC×SU(2)_R×SU(2)_L×SU(3)_c×U(1) and is more natural as far as supersymmetry breaking is concerned. Supersymmetry protects chiral symmetries from spontaneous breakdown and allows a solution to the strong CP problem. This model can accommodate at most three generations of quarks and leptons.     

Electromagnetic properties and decays of Dirac and Majorana neutrinos in a general class of gauge theories

We discuss the electromagnetic properties and decays of Dirac and Majorana neutrinos in a general class of gauge theories. Specific results for the standard SU(2)_L × U(1) and a (not necessarily left-right symmetric) SU(2)_L × SU(2)_R × U(1) theory are analyzed.     

The Voloshin-Vysotski-Okun solution to the solar-neutrino problem in a left-right model

The apparent anticorrelation between the solarneutrino flux and the sun-spot number can be explained if electron neutrino has a large magnetic moment. A model with SU(2) _L ×SU(2) _R ×U(1) _B?l gauge interaction is presented in which the electron neutrino has a large magnetic moment. The ingredients of the model are (i) the absence of the usual discrete left-right symmetry, (ii) new fermions that are singlets under SU(2) _L and SU(2) _R and (iii) two doublets and a charged singlet of higgs. The model utilises the see-saw mechanism of Gell-Mann, Ramond and Slansky give masses to all quarks and leptons. The large magnetic moment of the electron neutrino is achieved through charged singlet higgs fields.     

Small Dirac neutrino mass and left-right symmetry

We analyze the possibility of generating light Dirac neutrinos at the tree level in a left-right symmetric scenario. We present a minimal extension of the standard SU(2) _L × SU(2) _R × U(1) _Y′ model where the above result is achieved through a “see-saw” like mechanism induced by the minimization of the Higgs potential. The Dirac neutrinos thus obtained are naturally light; indeed we show that the scheme is stable under radiative corrections. The neutrino mass is inversely related to the scale of parity breaking, which may naturally be in the TeV range, leading to new phenomenology in an interesting energy domain.     

Gauge hierarchy in the presence of discrete symmetry

We discuss the gauge hierarchy problem in theories that posses an additional discrete symmetry. As examples, we consider two models based on the gauge groups U(1)_L×U(1)_Rand SU(2)_L×SU(2)_R×U(1), with parity transformation as the discrete symmetry. By employing a minimal choice of Higgs multiplets there is no freedom, in the semi-classical approximation, to arrange for an arbitrary hierarchy. Either one has a left-right symmetric phase (no hierarchy) or a totally asymmetric phase (infinite hierarchy). It is shown that radiative corrections, à la Coleman-Weinberg, do not smooth out the transition region separating the two phases. A finite gauge hierarchy is not realized.     

Gravity-induced weak symmetry breaking and supergravity

We give here a review of the recent developments of grand unified theories based onN=1 supergravity. We start with a brief introduction of supersymmetry and supergravity multiplets, and then discuss the construction of an invariant Lagrangian. The phenomena of gravity-induced weak symmetry breaking via the super Higgs effect at the tree level, corresponding to the conventional SU(5) gauge group, are then considered. We then extend this idea to the larger group SO(10), showing two possible breaking chains given as (i) SO(10)×susy→SU(2) _L ×U(1) _R ×U(1) _B-L ×SU(3) _C (≡ G₂₁₁₃)×susy→U(1)_em×SU(3) _C (G _LE ) predicting a secondZ-boson having mass lower than 1 TeV, and (ii) SO(10)×susy→SU(2) _L ×SU(2) _R ×SU(4)→(≡G₂₂₄)×susy→ SU(2) _L ×U(1) _Y ×SU(3) _C (≡ G₂₁₃)×susy→U(1)_em×SU(3) _C . We also consider the radiative breaking of weak symmetry via renormalisation group effects, which predicts the top quark mass. Some experimental signatures of the supersymmetric particles are investigated and possible future outlook is discussed. Invited talk presented at the International Symposium on Theoretical Physics, Bangalore, November 1984.     

Parity violation in SLAC experiment and left-right symmetric gauge models

It is shown that the left-right symmetric gauge models based on the group $\text{G}$ = SU(2)_L × SU(2)_R × U(1)_L × U(1)_R can accommodate quite naturally the results of the recent SLAC experiment concerning parity violation in neutral currents. The possibility of finding a light neutral gauge boson in the PETRA-PEP energy range remains particularly interesting.     

On the sign of the n-p mass difference in gauge models

We examine the sign of the n-p mass difference in some gauge models based on the SU(2) × U(1) × U(1) or SU(2)_L × SU(2)_R × U(1) group, and show that a few specific elements of the neutral-vector-meson mass matrix can determine the sign of Δm|_n?p. We also present an SU(2) × U(1) × U(1) model which can give the correct Δm|_n?p.     

Comments on the derivation of the mixing angles

It is pointed out that Fritzsch's derivation of the mixing angles for a six-quark theory based on a SU(2)_L × SU(2)_R × U(1) model is in error. The correct formula for the mixing angles differs significantly from Fritzsch's results.     

The Majoron and left-handed neutrino masses in SU(5)

We consider the spontaneous breaking of B?L in SU(5) in connection with left-handed neutrino masses. We show that the ensuing Goldstone boson, “the majoron”, is harmless. The low-energy predictions are the same as in the SU(2)_L × U(1) majoron model which, in particular, predicts the existence of doubly and singly charged scalars, with masses ?250 GeV and with a mass ratio of √2. Going to SU(5), one would expect these scalars to escape to the grand unified mass. This does not happen and, surprisingly, even the ratio √2 is preserved.     

A dynamical theory for the rishon model

We propose a composite model for quarks and leptons based on an exact SU(3)_C × SU(3)_H gauge theory and two fundamental $\text{J=}\text{1}\text{2}$ fermions: a charged T-rishon and a neutral V-rishon. Quarks, leptons and W-bosons are SU(3)_H-singlet composites of rishons. A dynamically broken effective SU(3)_C × SU(2)_L × SU(2)_R × U(1)_B?L gauge theory emerges at the composite level. The theory is “natural”, anomaly free, has no fundamental scalar particles, and describes at least three generations of quarks and leptons.     

Quark-lepton symmetry and B − L as the U(1) generator of the electroweak symmetry group

We seek an interpretation of the U(1) part of the electroweak symmetry group in terms of the quantum number B ? L. We show that the electroweak symmetry group, for which U(1) can be interpreted as a local B ? L symmetry, is the left-right symmetry group SU(2)_L × SU(2)_R × U(1)_L+R. The equating of U_L+R(1) to U_B?L(1) should lead to physical consequences which are not shared by standard gauge theory. B ? L may also help to explain the inversion of quark and lepton mass spectra.