Color Sextet Research Articles

Six-fermion ( B− L)-violating operators of arbitrary generational structure

We enumerate and construct the complete set of six-fermion SU(5)-invariant operators of arbitrary generational structure and prove that they, and, more generally, all six-fermion SU(3) c×SU(2) L×U(1) Y-invariant operators, violate ( B− L) and, in the standard theory with no ν R's, do so by ±2 units. The process for which the six-fermion SU(5)-invariant operators are most important is the n↔ n transition. Accordingly, we enumerate and construct the complete set of multigenerational six-quark B− B operators which are invariant under SU(3) c×SU(2) L×U(1) and SU(3) c×U(1) e.m. and determine which of these contribute to n↔ n transitions. An interesting result of this analysis is that the contributions of certain six-fermion operators containing higher-generation fields can dominate over those of entirely first-generation operators, despite mixing-angle suppression, because of much larger coefficient functions. Finally, we comment on the absolute n↔ n transition rate and derive a new lower bound on the masses of color sextet ( B− L)-violating Higgs bosons.

On models of weak interaction symmetry breaking by colour forces

Comments are made on models in which the Weinberg-Salam symmetry is broken by colour forces. In particular, we discuss the relevance of compositeness of quarks, leptons and new fermions (including a family of colour sextets).

On the Dynamical Problems and the Fermion Spectra in the Rishon Model

We propose to introduce a strong coupling U(l)y axial gauge boson into the rishon model which may explain dynamical problems concerning preservation of chiral symmetries and existence of solutions to anomaly conditions. Mechanisms through which exotic particles gain masses are discussed. It is found that exotic particles such as color octet leptons and color sextet quarks may gain masses ranging from 10 1 to 103. Some phenomenological aspects of these exotic particles are discussed.

Hydrogen-Antihydrogen Oscillations, Double Proton Decay, and Grand Unified Theories

The $\ensuremath{\Delta}B=\ensuremath{\Delta}L=2$ processes hydrogen-antihydrogen oscillation and $\mathrm{pp}\ensuremath{\rightarrow}{e}^{+}{e}^{+} or {\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{+}$ (double proton decay) in grand unified theories are examined. Although these reactions are very suppressed in the minimal SU(5) model, their rates may be significantly increased by appending a 50-plet of Higgs scalars. In that case relatively light color sextet and doubly charged colorless scalars might mediate $\mathrm{pp}\ensuremath{\rightarrow}{e}^{+}{e}^{+} or {\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{+}$ at a rate observable in ongoing proton decay experiments. Consequences of this scenario are discussed.

Fundamental fermion representations in generalisations of the SU(5) grand unified gauge theory

Generalisations of the SU(5) grand unified gauge theory are discussed. It is assumed that the gauge group is simple, and that the theory is both anomaly free and asymptotically free. All possible fundamental fermion representations are determined given that the fermions are massless at the unification level, but acquire mass at the level of the exact SU(3) × U(1) symmetry. No a priori restriction to standard colour SU(3) representations is made. It is found that E 6, SO(10) and SU( n) with n ⩾ 5 are the only acceptable gauge groups. Standard colour solutions are legion, but dull, incorporating at the SU(5) level, nothing other than p generations or copies of the familiar representation 10+ 5 . Exotic colour solutions are sparse, but interesting. Nine of these, all associated with SO(10), can accomodate those quarks and leptons currently thought to be fundamental, along with such things as colour sextets and octets, as well as doubly charged leptons.

The effect of Higgses and “technions” on the calculation of sin 2θw and Mx

The effect of the scalar sector on the calculation of sin 2 θ w and M x in grand unified theories is studied. We consider first elementary Higgs scalars and assume the “big desert” hypothesis. It is argued that Higgses other than the usual doublet can also be light (∼ M w). One can obtain bigger values for sin 2 θ w by having light (∼ M w) scalar colour sextets which can give rise to interesting phenomenology. As an example, one can build an SU(5) model giving sin 2 θ w ≅ 0.23 at the one-loop level. We also calculate the uncertainty in sin 2 θ w and M x due to the lack of knowledge of the specific masses of superheavy Higgses. We find that this uncertainty is small for reasonable SU(5) models but large in all the SO(10) versions except the minimal. Finally (and alternatively) we consider the effect of a technicolour interaction. The pseudo-Goldstone bosons (technions) increase the calculated sin 2 θ w by as much as ∼0.01 but M x remains nearly unchanged. Second-order contributions due to the technifermions tend to cancel the increase on sin 2 θ w and in turn increase M x.

A quixotic interpretation of the upsilon particle

We discuss the possibility that the upsilon particle is a Q Q bound state, where Q is a charge 1 3 , color sextet fermion. We explain why bound states of a Q with ordinary quarks and antiquarks might have escaped detection in accelerator searches for stable particles. We show that the Q and other bizarre fermions arise naturally in a unified theory in which the τ is a member of a weak SU(2) triplet.

Is thebquark a member of a color sextet?

Is the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>b</mml:mi></mml:math>quark a member of a color sextet?