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Failure to detect parity-nonconserving effects in atomic transitions coupled with the available neutrino neutral-current data would appear to rule out all SU (2) U (1) gauge theories which respect "natural" conservation laws for charm and strangeness and quark-lepton symmetry. We analyze a left-right symmetric "natural" (in the above sense) and quark-lepton symmetric SU (2) ₋ (2) ₑ (1) gauge theory and find that it accommodates all the features of neutral-current phenomena.
Mohapatra et al. (Mon,) studied this question.