Which version of PyMC are you using? I suggest using v4 if you are not yet.
init, which is now called init_dist requires an unnamed distribution as input so
alpha_zero = pm.Normal.dist(mu=0,sigma=np.sqrt(2), shape=(sample_shape,1))
The new version would have given you a more informative error to explain this.
PS: I haven’t checked the rest of you code.