Upper and lower estimates for the separation of solutions to fractional differential equations

Given a fractional differential equation of order $\alpha \in (0,1]$ with Caputo derivatives, we investigate in a quantitative sense how the associated solutions depend on their respective initial conditions. Specifically, we look at two solutions $x_1$ and $x_2$, say, of the same differential equation, both of which are assumed to be defined on a common interval $[0,T]$, and provide upper and lower bounds for the difference $x_1(t)-x_2(t)$ for all $t \in [0,T]$ that are stronger than the bounds previously described in the literature.