  For oscillatory functions on local fields coming from motivic exponential
functions, we show that integrability over $Q_p^n$ implies integrability over
$F_p ((t))^n$ for large $p$, and vice versa. More generally, the integrability
only depends on the isomorphism class of the residue field of the local field,
once the characteristic of the residue field is large enough. This principle
yields general local integrability results for Harish-Chandra characters in
positive characteristic as we show in other work. Transfer principles for
related conditions such as boundedness and local integrability are also
obtained. The proofs rely on a thorough study of loci of integrability, to
which we give a geometric meaning by relating them to zero loci of functions of
a specific kind.
