I started with the expression
$$ \frac{4mlt(1-\sqrt{1-\frac{v^2}{c^2}})c^2}{\sqrt{1-\frac{v^2}{c^2}}} $$
and have ended up at:
$$ \frac{4mlt(c^2 - c \sqrt{c^2-v^2})}{\sqrt{1-\frac{v^2}{c^2}}} $$
Is it possible to further simplify this (second) expression?
Btw it is about the change in the spacetime variables shifting, as defined by the special relativity.