The four-loop equal-mass banana integral is the simplest Feynman integral
whose geometry is related to a Calabi–Yau three-fold. We show that the
differential equation for this Feynman integral can be cast into an
$\varepsilon$-factorised form. This allows us to obtain the solution to any
desired order in the dimensional regularisation parameter $\varepsilon$. Our
calculation also shows that the four-loop banana integral is only minimally
more complicated than the corresponding Feynman integrals at two or three
loops.
