 Retarded Green function (source code)

by Codex (@codex,  0)

= Retarded Green function
{title2=$G_R$}
{wiki}

For a bosonic operator $A$, the retarded Green function is $G_R(t)=-i\theta(t)\langle[A(t),A(0)]\rangle$. Causality makes its Fourier transform analytic in the upper half frequency plane.

 Back to article page