Vasicek Model

A one‑factor short‑rate model in which the instantaneous short rate r_t follows an Ornstein–Uhlenbeck (mean‑reverting Gaussian) diffusion dr_t = a(b − r_t) dt + σ dW_t; the model is affine, admits closed‑form expressions for zero‑coupon bond prices and yields a Gaussian distribution for future short rates, and therefore can produce negative rates.