= Chiral transport equations in two spacetime dimensions
{title2=$(\partial_t+\partial_x)\psi_R=(\partial_t-\partial_x)\psi_L=0$}
The <massless Dirac equation> in one spatial dimension separates into opposite <chirality> sectors. Its initial profiles evolve as $\psi_R(t,x)=f(x-t)$ and $\psi_L(t,x)=h(x+t)$, by the <chain rule> along the straight characteristics. Thus <wave packets> translate without distortion at the <speed of light>. A nonzero <Dirac mass term> couples the two sectors, so these separate rigid-translation formulas do not apply to a massive field.
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