Left-right symmetry breaking in $E_6^L\times E_6^R$ occurs only in spacetime -- with possible implications for strong $CP$

Abstract

Two-sided octonionic $E_6^L\times E_6^R$ unification carries a nominal second colour $SU(3)_{c'}$ which, gauged, would colour the charged lepton and must be suppressed by hand. We argue no such device is needed: the left-right symmetry acts in spacetime, not internally -- in the gravi-weak reading $SU(2)_R$ is the gravitational frame group and the exchange is ordinary parity on the Dirac field; a spacetime operation cannot double the internal colour, so $SU(3)_{c'}=SU(3)_c$, one vector-like colour with a colour-singlet electron. The right sector contributes one colour-blind datum, $\sqrt m$ (values: the exceptional-Jordan trace split, an input; $N_R$ fixes only the colour representation). An anomaly no-go proven here shows every anomaly-free $U(1)$ on visible fermions lies in span$\{Q,B-L\}$, which the $\sqrt m$ pattern does not, in any sign or chirality assignment. The gauged dark-electromagnetic $U(1)_{dem}$ -- the mirror electroweak chain's unbroken remnant -- therefore carries the parity-mirror of electric charge on the dark sector: the visible fermions are dem-neutral (kinetic mixing the sole portal; no visible fifth force), and $\sqrt m$ enters visible physics only as the spectral label of the Jordan mass operator. The same recognition recovers hypercharge as the consistency relation $Y=Q-T^3_L$, $Q=N/3$, with no right-sector generator. As an application, the spontaneous parity forbids the QCD vacuum angle ($\theta_{QCD}=0$, conditional on the gravi-weak identification), while the flavour rotors have real determinant, so $\arg\det M=0$ at tree level (exact for the Cabibbo rung, texture-contingent in full), coexisting with a nonzero CKM phase. Loop stability -- where minimal gauged-$SU(2)_R$ parity solutions fail -- is plausibly evaded (no gauged $W_R$) but open, pending the Higgs-bridge matrix elements. We tag throughout what is derived, what is input, and what is open.