Title: On infinite order differential operators in fractional viscoelasticity,
Abstract: In this paper we discuss some general properties of viscoelastic models
defined in terms of constitutive equations involving infinitely many
derivatives (of integer and fractional order). In particular, we consider as a
working example the recently developed Bessel models of linear viscoelasticiy
that, for short times, behave like fractional Maxwell bodies of order $1/2$.