We prove the smoothness of the
-analytic
torsion form for fiber bundles with positive Novikov–Shubin invariant. We do so by
generalizing the arguments of Azzali, Goette and Schick to an appropriate Sobolev
space, and proving that the Novikov–Shubin invariant is also positive in the Sobolev
setting, using an argument of Alvarez Lopez and Kordyukov.