Consider the ellipse $$E$$ given by $$\dfrac{x^2}{18}+\dfrac{y^2}{12}=1$$. Let $$H$$ be the hyperbola whose eccentricity is the reciprocal of the eccentricity of $$E$$ and whose foci are the same as that of $$E$$. Let $$P$$ and $$Q$$ be the points of intersection of $$H$$ and the parabola $$\sqrt{5}\,y=x^2$$ in the first quadrant. Let $$d$$ be the distance between $$P$$ and $$Q$$.

If $$a$$ and $$b$$ are the integers such that $$d^2=a+b\sqrt{5}$$, then the value of $$a-b$$ is ___.