Neutral-current phenomena within the left-right-symmetric unified theory of quarks and leptons

Abstract

The neutral-current weak-interaction sector of the left-right-symmetric unified theory of quarks and leptons based on the symmetry structure $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\times \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_R\times \mathrm{SU}{\mathrm{}\left(4\right)\mathrm{}}_{L+R}^{\prime }$ and its subgroup $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\times \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_R\times \mathrm{SU}{\mathrm{}\left(3\right)\mathrm{}}_{L+R}^{\prime }\times \mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_{L+R}$ (suggested in earlier papers) is studied in detail here. The theory admits in general of two weak neutral gauge bosons $N_1$ and $N_2$ [and two sets of left and right charged $W\text{'}\mathrm{s}$ ($W_L^{\pm },W_R^{\pm }$)]. As pointed out earlier, there are two distinct possibilities for the pattern of spontaneous symmetry breaking which lead to the mass relations (i) $m_{N_1}^{}{}_{}{}^2\sim m_{W_L^{+}}^{}{}_{}{}^2\ll m_{N_2}^{}{}_{}{}^2$, (ii) $m_{N_1}^{}{}_{}{}^2\sim m_{N_2}^{}{}_{}{}^2\sim m_{W_L^{+}}^{}{}_{}{}^2$. Case (i) is identical to the familiar SU(2) × U(1) theory for all predictions. Case (ii), on the other hand, leads to departures from SU(2) × U(1). One of the crucial theorems following from our investigation is that such departures occur only for the electron-induced atomic parity experiments and not for neutrino-induced weak processes in the chiral ${\gamma }_5$-invariant limit, in which $W_L-W_R$ mixing as well as fermion masses vanish. In this manner (for the chiral limit defined above), SU(2) × U(1) becomes an integral and stable ingredient of the left-right-symmetric theory for both cases (i) and (ii) insofar as their predictions for neutrino-induced reactions are concerned; the differences between the two cases (in this chiral limit) lie solely in their predictions regarding atomic parity violation and, of course, the masses of the two neutral particles $N_1$ and $N_2$. We study the chiral as well as the nonchiral cases and compare their predictions with experiments, observing that approximate or exact global chiral symmetry of the left-right-symmetric theory is a point of good agreement between theory and all the present neutral-current experiments. We exhibit the dependence of the atomic parity-violation parameter

Keywords

• SYMMETRY
• N1 AND N2
• THEORY
• RIGHT
• CHARGED
• NEUTRAL GAUGE
• SYMMETRIC

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