# Langevin DE

by Niles
Tags: langevin
 P: 1,863 Hi I am reading about the Langevin stochastic differential equation $$\frac{d}{dt}p = -\alpha p + f(t)$$ where p is the momentum and f(t) the Langevin force. By definition =0 and = 2Dg(t-t'), where g is the second order correlation function. My question is, why is there a factor 2 in the expression for ? I can't seem to find an answer in any book, but they all write the factor. I would be glad to recieve some feedback. Best, Niles.