= Outgoing analytic branch of Klein-Gordon step momentum
{title2=$q(z)=\sqrt{z-mc^2}\sqrt{z+mc^2}/(\hbar c)$}
Set $z=E-V_0+i0$ and continue both roots from the <upper half-plane>. The right-hand wavenumber is positive above the positive-energy threshold, positive imaginary inside the gap, and negative below the negative-energy threshold. Its <group velocity> in the last region remains rightward because both <momentum> and <kinetic energy> are negative. Choosing a positive real root there instead specifies an incoming wavepacket from the right.
Back to article page
